Don't call transform_apply on cameras in Geometry.clear_scale

clear_scale routed camera, light and speaker objects into
bpy.ops.object.transform_apply, which cannot act on that data. It reported
"Objects have no data to transform" and left the scale untouched -- the no-op the
docstring already describes when it says clearing scale has no impact on cameras.

Besides the warning spam on every drawing camera update, the call is a crash
vector: transform_apply resolves bpy.context from inside the temp_override, and
that has been seen to segfault (EXCEPTION_ACCESS_VIOLATION in
BPY_context_member_get, via ctx_wm_python_context_get) when reached from a
UI-invoked operator through bim.update_representation on a drawing camera.

Return early for those data types instead. Behaviour is unchanged, since the
operator was already doing nothing for them.

Generated with the assistance of an AI coding tool.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/bonsai/bonsai/bim/module/drawing/prop.py

@@ -671,7 +671,13 @@ class BIMCameraProperties(PropertyGroup):
         # Rounding is necessary to avoid float garbage differences
         # forcing unnecessary representation update.
         def round_(f: float) -> float:
-            return round(f, 6)
+            # "+ 0.0" normalises -0.0 to 0.0. round() keeps the sign of zero and
+            # json.dumps writes it out as "-0.0", so without this a matrix differing
+            # only in a zero's sign serialises to a different string forever: the
+            # cached blob never matches and the camera datablock is rebuilt on every
+            # create_drawing (resetting every PropertyGroup on it). Reflected plan
+            # views hit this because get_camera_shape_matrix negates mat[1][1].
+            return round(f, 6) + 0.0
 
         representation = json.dumps(
             {

src/bonsai/bonsai/tool/geometry.py

@@ -350,6 +350,15 @@ class Geometry(bonsai.core.tool.Geometry):
         Note that clearing scale has no impact on cameras.
         """
         if cls.is_scaled(obj):
+            if isinstance(obj.data, (bpy.types.Camera, bpy.types.Light, bpy.types.Speaker)):
+                # object.transform_apply cannot touch this data -- it just reports
+                # "Objects have no data to transform" and leaves the scale alone, which
+                # is why the docstring says cameras are unaffected. Skipping the call
+                # keeps that behaviour and avoids the operator resolving bpy.context
+                # from inside the temp_override below, which has been seen to segfault
+                # (EXCEPTION_ACCESS_VIOLATION in BPY_context_member_get) when reached
+                # from a UI-invoked operator via bim.update_representation.
+                return
             if not obj.data:
                 location, rotation, _ = obj.matrix_world.decompose()
                 obj.matrix_world = Matrix.Translation(location) @ rotation.to_matrix().to_4x4()

src/ifcopenshell-python/ifcopenshell/api/alignment/__init__.py

@@ -25,7 +25,7 @@ are automatically created and maintained.
 
 Alignments are created with stationing referents. Each layout segment is assigned a position referent that informs about
 the start point of the segment. An example is the point of curvature of a horizontal circular curve. The referent is
-nested to the segment representing the circular arc and is named with a indicator of the position and the station, e.g. "P.C. (145+98.32)"
+nested to the segment representing the circular arc and is named with the alignment name and an indicator of the position and the station, e.g. "MyAlignment 145+98.32 (P.C.)"
 
 This API does not determine alignment parameters based on rules, such as minimum curve radius as a function of design speed or sight distance.
 
@@ -89,6 +89,7 @@ from .layout_vertical_alignment_by_pi_method import (
     layout_vertical_alignment_by_pi_method,
 )
 from .name_segments import name_segments
+from .update_alignment_parameter_segment_tags import update_alignment_parameter_segment_tags
 from .update_end_point import update_end_point
 from .update_fallback_position import update_fallback_position
 from .update_key_point_referents import update_key_point_referents
@@ -132,6 +133,7 @@ __all__ = [
     "layout_vertical_alignment_by_pi_method",
     "name_segments",
     "register_referent_name_callback",
+    "update_alignment_parameter_segment_tags",
     "update_end_point",
     "update_fallback_position",
     "update_key_point_referents",

src/ifcopenshell-python/ifcopenshell/api/alignment/_get_key_point_tag.py

@@ -0,0 +1,30 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2025 Thomas Krijnen <thomas@aecgeeks.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import ifcopenshell
+import ifcopenshell.util.alignment
+
+
+def _get_key_point_tag(file: ifcopenshell.file, label: str, station: float) -> str:
+    """
+    Builds the station-and-label text shared by update_alignment_parameter_segment_tags (used
+    directly as IfcAlignmentParameterSegment.StartTag/EndTag) and update_key_point_referents (used,
+    prefixed with the alignment name, as IfcReferent.Name): "<station> (<label>)", e.g.
+    "145+98.32 (P.O.B.)".
+    """
+    return f"{ifcopenshell.util.alignment.station_as_string(file, station)} ({label})"

src/ifcopenshell-python/ifcopenshell/api/alignment/create.py

@@ -51,6 +51,10 @@ def create(
 
     If geometric representations are created, the alignment stationing referent is also created using the start_station value. IfcReferent.ObjectPlacement
     is required for linear positiion elements and IfcLinearPlacement is defined relative to alignment curve geometry.
+    This referent's Name follows the same "<alignment name> <station>" convention update_key_point_referents() uses
+    for its own key-point referents (e.g. "MyAlignment 49+00.00"), so that every referent nested under an alignment
+    is identifiable by name alone, without needing to inspect its Pset_Stationing or placement to know which
+    alignment it belongs to.
 
     :param file:
     :param name: name assigned to IfcAlignment.Name
@@ -86,7 +90,7 @@ def create(
     if include_geometry:
         _create_geometric_representation(file, alignment)
 
-    referent_name = ifcopenshell.util.alignment.station_as_string(file, start_station)
+    referent_name = f"{name} {ifcopenshell.util.alignment.station_as_string(file, start_station)}"
     referent = ifcopenshell.api.alignment.add_stationing_referent(file, referent_name, alignment, 0.0, start_station)
 
     for layout in alignment_layouts:

src/ifcopenshell-python/ifcopenshell/api/alignment/create_as_polyline.py

@@ -128,6 +128,11 @@ def create_as_polyline(
 
     The IfcAlignment is aggreated to IfcProject
 
+    The stationing referent created from start_station has Name "<alignment name> <station>"
+    (e.g. "MyAlignment 49+00.00"), the same convention update_key_point_referents() and
+    create() use for their own referents, so every referent nested under an alignment is
+    identifiable by name alone.
+
     :param file:
     :param name: name assigned to IfcAlignment.Name
     :param points: sequence of points defining the polyline
@@ -142,8 +147,8 @@ def create_as_polyline(
     _create_polyline_representation(file, alignment, points)
 
     # define stationing
-    name = ifcopenshell.util.alignment.station_as_string(file, start_station)
-    referent = ifcopenshell.api.alignment.add_stationing_referent(file, name, alignment, 0.0, start_station)
+    referent_name = f"{alignment.Name} {ifcopenshell.util.alignment.station_as_string(file, start_station)}"
+    referent = ifcopenshell.api.alignment.add_stationing_referent(file, referent_name, alignment, 0.0, start_station)
 
     # IFC 4.1.4.1.1 Alignment Aggregation To Project
     project = file.by_type("IfcProject")[0]

src/ifcopenshell-python/ifcopenshell/api/alignment/update_alignment_parameter_segment_tags.py

@@ -0,0 +1,108 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2025 Thomas Krijnen <thomas@aecgeeks.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import ifcopenshell
+import ifcopenshell.api.alignment
+from ifcopenshell import entity_instance
+from ifcopenshell.api.alignment._get_key_point_tag import _get_key_point_tag
+from ifcopenshell.api.alignment._get_segment_start_point_label import (
+    _get_segment_start_point_label,
+)
+
+
+def update_alignment_parameter_segment_tags(
+    file: ifcopenshell.file, layout: entity_instance, label_end_tag: bool = False
+) -> None:
+    """
+    Sets IfcAlignmentParameterSegment.StartTag (and, optionally, EndTag) for every segment
+    transition in an alignment layout. Unlike update_key_point_referents, this does not create any
+    IfcReferent or IfcRelNests -- it only mutates the StartTag/EndTag string attributes already
+    present on each segment's DesignParameters.
+
+    Every real segment's StartTag is set to a computed tag describing the point where it begins,
+    using the same label-and-station format as update_key_point_referents' Name minus the alignment
+    name (via _get_key_point_tag), e.g. "145+98.32 (P.C.)". The first segment's StartTag comes from
+    the "Beginning of Alignment" boundary label.
+
+    EndTag is left untouched unless `label_end_tag` is True. When enabled, for each transition
+    between two consecutive segments, the outgoing segment's EndTag is set to the same tag as the
+    incoming segment's StartTag (they describe the same physical point), and the last segment's
+    EndTag is set from the "End of Alignment" boundary label.
+
+    Labels come from _get_segment_start_point_label -- if a callback has been registered via
+    register_referent_name_callback(), its output is used instead of the built-in labels, exactly as
+    in update_key_point_referents.
+
+    :param layout: IfcAlignmentHorizontal, IfcAlignmentVertical, or IfcAlignmentCant
+    :param label_end_tag: if True, also sets EndTag on every real segment. If False (default),
+        EndTag is left untouched.
+    :return: None -- this function mutates segment.DesignParameters.StartTag/EndTag in place
+
+    Example:
+
+    .. code:: python
+
+        horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+        ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(model, horizontal)
+    """
+
+    expected_types = ["IfcAlignmentHorizontal", "IfcAlignmentVertical", "IfcAlignmentCant"]
+    if not layout.is_a() in expected_types:
+        raise TypeError(
+            f"Expected entity type to be one of {[_ for _ in expected_types]}, instead received {layout.is_a()}"
+        )
+
+    alignment = ifcopenshell.api.alignment.get_alignment(layout)
+    if alignment is None:
+        raise ValueError(f"{layout.is_a()} #{layout.id()} is not nested under an IfcAlignment.")
+
+    segments = list(ifcopenshell.api.alignment.get_layout_segments(layout))
+    if segments and ifcopenshell.api.alignment.has_zero_length_segment(layout):
+        segments = segments[:-1]
+
+    if not segments:
+        return
+
+    start_station = ifcopenshell.api.alignment.get_alignment_start_station(file, alignment)
+    is_horizontal = layout.is_a("IfcAlignmentHorizontal")
+
+    distance_along = 0.0
+    prev_segment = None
+    for segment in segments:
+        dp = segment.DesignParameters
+        seg_distance_along = distance_along if is_horizontal else dp.StartDistAlong
+
+        label = _get_segment_start_point_label(prev_segment, segment)
+        station = start_station + seg_distance_along
+        tag = _get_key_point_tag(file, label, station)
+
+        dp.StartTag = tag
+        if prev_segment is not None and label_end_tag:
+            prev_segment.DesignParameters.EndTag = tag
+
+        if is_horizontal:
+            distance_along += dp.SegmentLength
+        else:
+            distance_along = dp.StartDistAlong + dp.HorizontalLength
+
+        prev_segment = segment
+
+    if label_end_tag:
+        label = _get_segment_start_point_label(prev_segment, None)
+        station = start_station + distance_along
+        prev_segment.DesignParameters.EndTag = _get_key_point_tag(file, label, station)

src/ifcopenshell-python/ifcopenshell/api/alignment/update_key_point_referents.py

@@ -22,9 +22,9 @@ import ifcopenshell
 import ifcopenshell.api.alignment
 import ifcopenshell.api.pset
 import ifcopenshell.guid
-import ifcopenshell.util.alignment
 import ifcopenshell.util.element
 from ifcopenshell import entity_instance
+from ifcopenshell.api.alignment._get_key_point_tag import _get_key_point_tag
 from ifcopenshell.api.alignment._get_segment_start_point_label import (
     _get_segment_start_point_label,
 )
@@ -32,21 +32,6 @@ from ifcopenshell.api.alignment._sort_nest import _sort_nest
 from ifcopenshell.api.alignment.update_fallback_position import update_fallback_position
 
 
-def _get_key_point_referent_nest(layout: entity_instance) -> Optional[entity_instance]:
-    """
-    Searches layout.IsNestedBy for the IfcRelNests whose RelatedObjects are IfcReferent.
-
-    This is distinct from both get_stationing_nest (scoped to the parent IfcAlignment, and
-    specifically the STATION/station-equation nest) and get_alignment_segment_nest (the *segment*
-    nest that also lives on layout.IsNestedBy, holding IfcAlignmentSegment, never IfcReferent).
-    """
-    for nest in layout.IsNestedBy:
-        for related_object in nest.RelatedObjects:
-            if related_object.is_a("IfcReferent"):
-                return nest
-    return None
-
-
 def _remove_referent(file: ifcopenshell.file, referent: entity_instance) -> None:
     """Cleanly deletes a key-point IfcReferent: its Pset_Stationing, its ObjectPlacement (if
     exclusively owned by it), and finally the referent itself."""
@@ -91,7 +76,7 @@ def _create_key_point_referent(
             ),
         )
 
-    name = f"{label} ({ifcopenshell.util.alignment.station_as_string(file, station)})"
+    name = f"{alignment.Name} {_get_key_point_tag(file, label, station)}"
 
     referent = file.createIfcReferent(
         GlobalId=ifcopenshell.guid.new(),
@@ -120,7 +105,8 @@ def update_key_point_referents(
     Creates IfcReferent key-point markers for every segment transition in an alignment layout.
 
     Labels are derived from _get_segment_start_point_label (e.g. "P.C.", "P.T.", "P.O.B.",
-    "P.V.C.", ...), with the station appended, e.g. "P.C. (145+98.32)". Different jurisdictions use
+    "P.V.C.", ...), and combined with the alignment name and station to build the Name, e.g.
+    "MyAlignment 145+98.32 (P.C.)". Different jurisdictions use
     different naming systems for these key points -- register_referent_name_callback() lets a
     caller override the default horizontal/vertical/cant labeling before calling this function; if
     a callback is registered, its output is used here instead of the built-in labels. Referents are
@@ -129,9 +115,19 @@ def update_key_point_referents(
     get_stationing_nest) -- key-point referents never belong in either of those.
 
     :param layout: IfcAlignmentHorizontal, IfcAlignmentVertical, or IfcAlignmentCant
-    :param rel_nests: an existing IfcRelNests to (re)populate. May live anywhere (e.g. the parent
-        IfcAlignment, the layout, or elsewhere) -- the caller decides. If omitted, an existing
-        referent-nest already on `layout` is reused, or a new one is created and related to `layout`.
+    :param rel_nests: an existing IfcRelNests to (re)populate; its RelatingObject must be an
+        IfcAlignment (TypeError is raised otherwise), but need not be the IfcAlignment that
+        directly nests `layout` -- passing an ancestor's own IfcRelNests is supported
+        specifically so that a vertical/cant layout living under a child IfcAlignment (per CT
+        4.1.4.4.1.2, once a second vertical layout is added) can still have its key-point
+        referents named after and nested to the top-level parent alignment, matching how the
+        alignment's horizontal key points are named, rather than a generic "Child of X" name.
+        When `rel_nests` is given, `rel_nests.RelatingObject` -- not `layout`'s own direct
+        parent -- is used for both the created referents' Name and the returned IfcRelNests. If
+        omitted, a new IfcRelNests is always created and related to `layout`'s own direct
+        parent alignment -- there is no implicit search for or reuse of a previously created
+        nest. Callers who want to regenerate into an existing nest must pass it back in
+        explicitly via `rel_nests`.
     :param clear: if True, deletes all IfcReferent currently in rel_nests.RelatedObjects (and their
         Pset_Stationing) before regenerating. If False (default), new referents are appended to
         whatever already exists -- no deduplication.
@@ -158,7 +154,7 @@ def update_key_point_referents(
         ifcopenshell.api.alignment.register_referent_name_callback(horizontal=my_horizontal_labels)
         horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
         nest = ifcopenshell.api.alignment.update_key_point_referents(model, horizontal)
-        # nest.RelatedObjects[0].Name starts with "Start (" instead of the default "P.O.B. ("
+        # nest.RelatedObjects[0].Name ends with "(Start)" instead of the default "(P.O.B.)"
     """
 
     expected_types = ["IfcAlignmentHorizontal", "IfcAlignmentVertical", "IfcAlignmentCant"]
@@ -167,12 +163,28 @@ def update_key_point_referents(
             f"Expected entity type to be one of {[_ for _ in expected_types]}, instead received {layout.is_a()}"
         )
 
-    if rel_nests is None:
-        rel_nests = _get_key_point_referent_nest(layout)
-        if rel_nests is None:
-            rel_nests = file.createIfcRelNests(
-                GlobalId=ifcopenshell.guid.new(), RelatingObject=layout, RelatedObjects=()
+    layout_alignment = ifcopenshell.api.alignment.get_alignment(layout)
+    if layout_alignment is None:
+        raise ValueError(f"{layout.is_a()} #{layout.id()} is not nested under an IfcAlignment.")
+
+    # `alignment` is used below for referent naming (and as the fallback-placement basis) --
+    # it defaults to layout's own direct parent, but an explicitly passed rel_nests overrides
+    # it with rel_nests.RelatingObject instead (see the rel_nests docstring above). Station
+    # computation always uses layout_alignment, unaffected by this -- get_alignment_start_station
+    # already walks up to the true top-level alignment's own stationing referent regardless of
+    # which (possibly child) alignment it's given.
+    if rel_nests is not None:
+        if not rel_nests.RelatingObject.is_a("IfcAlignment"):
+            raise TypeError(
+                f"Expected rel_nests.RelatingObject to be IfcAlignment, instead received "
+                f"{rel_nests.RelatingObject.is_a()}"
             )
+        alignment = rel_nests.RelatingObject
+    else:
+        alignment = layout_alignment
+        rel_nests = file.createIfcRelNests(
+            GlobalId=ifcopenshell.guid.new(), RelatingObject=alignment, RelatedObjects=()
+        )
 
     if clear:
         for referent in list(rel_nests.RelatedObjects):
@@ -189,8 +201,7 @@ def update_key_point_referents(
         )
         return rel_nests
 
-    alignment = ifcopenshell.api.alignment.get_alignment(layout)
-    start_station = ifcopenshell.api.alignment.get_alignment_start_station(file, alignment)
+    start_station = ifcopenshell.api.alignment.get_alignment_start_station(file, layout_alignment)
     curve = ifcopenshell.api.alignment.get_layout_curve(layout)
     is_horizontal = layout.is_a("IfcAlignmentHorizontal")
 

src/ifcopenshell-python/ifcopenshell/api/sequence/create_baseline.py

@@ -28,7 +28,7 @@ import ifcopenshell.util.sequence
 
 def create_baseline(
     file: ifcopenshell.file, work_schedule: ifcopenshell.entity_instance, name: Optional[str] = None
-) -> None:
+) -> ifcopenshell.entity_instance:
     """Creates a baseline for your Work Schedule
 
     Using a IfcWorkSchdule having PredefinedType=PLANNED,
@@ -42,7 +42,7 @@ def create_baseline(
     * Same Construction Resources
     * Same Resource Relationships
 
-    :param work_schedule: The planned work_schedule to baseline
+    :param work_schedule: The planned work schedule to baseline
     :param name: baseline work schedule name
     :return: The baseline work_schedule
 
@@ -51,7 +51,7 @@ def create_baseline(
     .. code:: python
 
         # We have a Work Schedule
-        planned_work_schedule = WorkSchedule(name="Design new feature",predefinedType="PLANNED", deadline="2023-03-01")
+        planned_work_schedule = ifcopenshell.api.sequence.add_work_schedule(model, name="Planned Construction Schedule")
 
         # And now we have a baseline for our Work Schedule
         baseline_work_schedule = ifcopenshell.api.sequence.create_baseline(file, work_schedule=planned_work_schedule, name="Baseline 1")
@@ -64,24 +64,23 @@ def create_baseline(
 class Usecase:
     file: ifcopenshell.file
 
-    def execute(self, work_schedule: ifcopenshell.entity_instance, name: Union[str, None]) -> None:
-        # create work schedule
-        if not work_schedule.PredefinedType == "PLANNED":
-            return
+    def execute(
+        self, work_schedule: ifcopenshell.entity_instance, name: Union[str, None]
+    ) -> ifcopenshell.entity_instance:
+        if work_schedule.PredefinedType != "PLANNED":
+            raise ValueError("Only a PLANNED work schedule can be baselined.")
         baseline_work_schedule = ifcopenshell.api.sequence.add_work_schedule(
-            self.file, name=work_schedule.Name, predefined_type="BASELINE"
+            self.file, name=name or work_schedule.Name, predefined_type="BASELINE"
         )
-        baseline_work_schedule.Name = name
         self.create_baseline_reference(work_schedule, baseline_work_schedule)
         for summary_task in ifcopenshell.util.sequence.get_root_tasks(work_schedule):
-            res = ifcopenshell.api.sequence.duplicate_task(self.file, task=summary_task)
-            assert isinstance(res, list)
-            current, duplicate = res
+            current, duplicate = ifcopenshell.api.sequence.duplicate_task(self.file, task=summary_task)
             ifcopenshell.api.control.assign_control(
                 self.file, relating_control=baseline_work_schedule, related_objects=[duplicate[0]]
             )
             for i, task in enumerate(current):
                 self.create_baseline_reference(task, duplicate[i])
+        return baseline_work_schedule
 
     def create_baseline_reference(
         self, relating_object: ifcopenshell.entity_instance, related_object: ifcopenshell.entity_instance

src/ifcopenshell-python/ifcopenshell/util/alignment.py

@@ -69,21 +69,21 @@ def station_as_string(file: ifcopenshell.file, sta: float):
     Returns a stringized version of a station. Example 100.0 is 1+00.00 as a stationing string.
     If the project units are SI-based, the string is in the format xxx+yyy.zzz
     If the project units are Emperial-based, the string is in the format xx+yy.zz
+
     :param station: the station to be stringized
     :return: stringized station
     """
 
     unit_type = ifcopenshell.util.unit.get_project_unit(file, "LENGTHUNIT")
+    project_unit_to_metres = ifcopenshell.util.unit.calculate_unit_scale(file)
     if unit_type.is_a("IfcConversionBasedUnit"):
-        station = ifcopenshell.util.unit.convert(
-            sta, from_unit=unit_type.Name, from_prefix=None, to_unit="foot", to_prefix=None
-        )
+        # xx+yy.zz display is inherently foot-based, regardless of which foot variant
+        # (international vs. US survey, etc.) the project's own unit actually is.
+        station = sta * project_unit_to_metres / 0.3048
         plus_seperator = 2
         precision = 2
     else:
-        station = ifcopenshell.util.unit.convert(
-            sta, from_unit=unit_type.Name, from_prefix=unit_type.Prefix, to_unit="meter", to_prefix=None
-        )
+        station = sta * project_unit_to_metres
         plus_seperator = 3
         precision = 3
 

src/ifcopenshell-python/ifcopenshell/util/unit.py

@@ -720,7 +720,29 @@ def calculate_unit_scale(ifc_file: ifcopenshell.file, unit_type: str = "LENGTHUN
             unit_scale *= conversion_factor.ValueComponent.wrappedValue
             unit = conversion_factor.UnitComponent
         if unit.is_a("IfcSIUnit"):
-            unit_scale *= get_prefix_multiplier(unit.Prefix)
+            prefix_multiplier = get_prefix_multiplier(unit.Prefix)
+            # An SI prefix attaches to the base unit symbol, and the prefixed
+            # symbol is raised to the power as a whole: dm3 = (dm)3 = 1e-3 m3,
+            # not 0.1 m3. For units whose dimensions are a pure power of length
+            # (METRE, SQUARE_METRE, CUBIC_METRE) the prefix multiplier must
+            # therefore be raised to the length exponent. Units with mixed or
+            # non-length dimensions (PASCAL, NEWTON, GRAM, ...) keep the linear
+            # multiplier, as there the prefix scales the derived unit itself.
+            # https://github.com/IfcOpenShell/IfcOpenShell/issues/9278
+            dimensions = unit.Dimensions
+            length_exponent = dimensions.LengthExponent
+            if length_exponent > 0 and not any(
+                (
+                    dimensions.MassExponent,
+                    dimensions.TimeExponent,
+                    dimensions.ElectricCurrentExponent,
+                    dimensions.ThermodynamicTemperatureExponent,
+                    dimensions.AmountOfSubstanceExponent,
+                    dimensions.LuminousIntensityExponent,
+                )
+            ):
+                prefix_multiplier **= length_exponent
+            unit_scale *= prefix_multiplier
     return unit_scale
 
 
@@ -940,7 +962,8 @@ def convert_file_length_units(ifc_file: ifcopenshell.file, target_units: str = "
         )
 
     unit_assignment = get_unit_assignment(file_patched)
-    unit_assignment.Units = [new_length, *(u for u in unit_assignment.Units if u.UnitType != new_length.UnitType)]
+    # UnitType not available on IfcMonetaryUnit
+    unit_assignment.Units = [new_length, *(u for u in unit_assignment.Units if getattr(u, 'UnitType', None) != new_length.UnitType)]
     if not file_patched.get_total_inverses(old_length):
         ifcopenshell.util.element.remove_deep2(file_patched, old_length)
 

src/ifcopenshell-python/test/api/alignment/test_add_stationing_to_alignment.py

@@ -43,7 +43,7 @@ def test_add_stationing_to_alignment():
     referent = stationing_nest.RelatedObjects[0]
 
     assert referent.PredefinedType == "STATION"
-    assert referent.Name == "2+000.000"
+    assert referent.Name == "TestAlignment 2+000.000"
     assert ifcopenshell.util.element.get_pset(element=referent, name="Pset_Stationing")
     assert ifcopenshell.util.element.get_pset(element=referent, name="Pset_Stationing", prop="Station") == 2000.0
     assert referent.ObjectPlacement != None

src/ifcopenshell-python/test/api/alignment/test_create.py

@@ -20,6 +20,39 @@
 import ifcopenshell.api.alignment
 import ifcopenshell.api.context
 import ifcopenshell.api.unit
+import ifcopenshell.util.element
+
+
+def test_create_stationing_referent_name_includes_alignment_name():
+    """create() creates an initial stationing IfcReferent from start_station
+    (see add_stationing_referent()). Its Name must include the alignment's
+    own name, the same "<alignment name> <station>" convention
+    update_key_point_referents() uses for its own referents -- otherwise
+    this referent is indistinguishable by name alone from the same-named
+    referent of any OTHER alignment in the same file, unlike every other
+    referent in the model."""
+    file = ifcopenshell.file(schema="IFC4X3_ADD2")
+    project = file.createIfcProject(GlobalId=ifcopenshell.guid.new(), Name="Test")
+    length = ifcopenshell.api.unit.add_conversion_based_unit(file, name="foot")
+    ifcopenshell.api.unit.assign_unit(file, units=[length])
+    geometric_representation_context = ifcopenshell.api.context.add_context(file, context_type="Model")
+    ifcopenshell.api.context.add_context(
+        file,
+        context_type="Model",
+        context_identifier="Axis",
+        target_view="MODEL_VIEW",
+        parent=geometric_representation_context,
+    )
+
+    alignment = ifcopenshell.api.alignment.create(file, "TestAlignment", start_station=4900.0)
+
+    referents = [
+        r
+        for r in ifcopenshell.util.element.get_components(alignment)
+        if r.is_a("IfcReferent") and ifcopenshell.util.element.get_pset(r, name="Pset_Stationing", prop="Station") == 4900.0
+    ]
+    assert len(referents) == 1
+    assert referents[0].Name == "TestAlignment 49+00.00"
 
 
 def test_create():
@@ -84,3 +117,4 @@ def test_create():
 
 
 test_create()
+test_create_stationing_referent_name_includes_alignment_name()

src/ifcopenshell-python/test/api/alignment/test_create_as_polyline.py

@@ -19,6 +19,7 @@
 
 import ifcopenshell.api.alignment
 import ifcopenshell.api.unit
+import ifcopenshell.util.element
 
 
 def test_create_as_polyline():
@@ -40,10 +41,19 @@ def test_create_as_polyline():
         file.createIfcCartesianPoint((-585.0, 3275.2, 56.2)),
     ]
 
-    alignment = ifcopenshell.api.alignment.create_as_polyline(file, "A1", points)
+    alignment = ifcopenshell.api.alignment.create_as_polyline(file, "A1", points, start_station=100.0)
     curve = ifcopenshell.api.alignment.get_curve(alignment)
     assert curve.is_a("IfcPolyline")
     assert len(curve.Points) == 10
 
+    # stationing referent's Name must include the alignment's own name, the
+    # same "<alignment name> <station>" convention create() and
+    # update_key_point_referents() use -- previously this reassigned the
+    # local `name` variable (shadowing the "A1" parameter) to just the bare
+    # station string, losing the alignment name entirely.
+    referents = [r for r in ifcopenshell.util.element.get_components(alignment) if r.is_a("IfcReferent")]
+    assert len(referents) == 1
+    assert referents[0].Name == "A1 0+100.000"
+
 
 test_create_as_polyline()

src/ifcopenshell-python/test/api/alignment/test_referent_names.py

@@ -96,6 +96,10 @@ def callback_alignment():
     yield alignment
 
 
+def _label(name):
+    return name.rsplit("(", 1)[1].rstrip(")")
+
+
 def test_with_default_names(default_names_alignment):
     file = default_names_alignment.file
     horizontal = ifcopenshell.api.alignment.get_horizontal_layout(default_names_alignment)
@@ -107,8 +111,8 @@ def test_with_default_names(default_names_alignment):
     expected_h = ["P.O.B.", "P.C.", "P.T.", "P.C.", "P.T.", "P.C.", "P.T.", "P.O.E."]
     expected_v = ["V.P.O.B.", "P.V.C.", "P.V.T.", "P.V.C.", "P.V.T.", "P.V.C.", "P.V.T.", "P.V.C.", "P.V.T.", "V.P.O.E."]
 
-    assert [r.Name.split(" (")[0] for r in h_nest.RelatedObjects] == expected_h
-    assert [r.Name.split(" (")[0] for r in v_nest.RelatedObjects] == expected_v
+    assert [_label(r.Name) for r in h_nest.RelatedObjects] == expected_h
+    assert [_label(r.Name) for r in v_nest.RelatedObjects] == expected_v
 
 
 def test_with_callbacks(callback_alignment):
@@ -122,7 +126,7 @@ def test_with_callbacks(callback_alignment):
     expected_h = ["A", "Q", "Q", "Q", "Q", "Q", "Q", "Z"]
     expected_v = ["a", "q", "q", "q", "q", "q", "q", "q", "q", "z"]
 
-    assert [r.Name.split(" (")[0] for r in h_nest.RelatedObjects] == expected_h
-    assert [r.Name.split(" (")[0] for r in v_nest.RelatedObjects] == expected_v
+    assert [_label(r.Name) for r in h_nest.RelatedObjects] == expected_h
+    assert [_label(r.Name) for r in v_nest.RelatedObjects] == expected_v
 
     ifcopenshell.api.alignment.register_referent_name_callback(None, None, None)  # reset global state

src/ifcopenshell-python/test/api/alignment/test_update_alignment_parameter_segment_tags.py

@@ -0,0 +1,307 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2025 Thomas Krijnen <thomas@aecgeeks.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import pytest
+
+import ifcopenshell.api.alignment
+import ifcopenshell.api.context
+import ifcopenshell.api.unit
+import ifcopenshell.util.alignment
+
+COORDINATES = [(500.0, 2500.0), (3340.0, 660.0), (4340.0, 5000.0), (7600.0, 4560.0), (8480.0, 2010.0)]
+RADII = [1000.0, 1250.0, 950.0]
+VPOINTS = [(0.0, 100.0), (2000.0, 135.0), (5000.0, 105.0), (7400.0, 153.0), (9800.0, 105.0), (12800.0, 90.0)]
+LENGTHS = [1600.0, 1200.0, 2000.0, 800.0]
+
+
+def _new_file():
+    file = ifcopenshell.file(schema="IFC4X3")
+    file.createIfcProject(GlobalId=ifcopenshell.guid.new(), Name="Test")
+    length = ifcopenshell.api.unit.add_si_unit(file, unit_type="LENGTHUNIT")
+    ifcopenshell.api.unit.assign_unit(file, units=[length])
+    geometric_representation_context = ifcopenshell.api.context.add_context(file, context_type="Model")
+    ifcopenshell.api.context.add_context(
+        file,
+        context_type="Model",
+        context_identifier="Axis",
+        target_view="MODEL_VIEW",
+        parent=geometric_representation_context,
+    )
+    return file
+
+
+def _new_file_no_context():
+    file = ifcopenshell.file(schema="IFC4X3")
+    file.createIfcProject(GlobalId=ifcopenshell.guid.new(), Name="Test")
+    length = ifcopenshell.api.unit.add_si_unit(file, unit_type="LENGTHUNIT")
+    ifcopenshell.api.unit.assign_unit(file, units=[length])
+    return file
+
+
+def _build_alignment(file, start_station=0.0):
+    return ifcopenshell.api.alignment.create_by_pi_method(
+        file, "TestAlignment", COORDINATES, RADII, VPOINTS, LENGTHS, start_station
+    )
+
+
+def _real_segments(layout):
+    segments = ifcopenshell.api.alignment.get_layout_segments(layout)
+    return segments[:-1] if ifcopenshell.api.alignment.has_zero_length_segment(layout) else segments
+
+
+def _label(tag):
+    return tag.rsplit("(", 1)[1].rstrip(")")
+
+
+def test_wrong_layout_type_raises_type_error():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    with pytest.raises(TypeError):
+        ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, alignment)
+
+
+def test_not_nested_under_alignment_raises_value_error():
+    file = _new_file_no_context()
+    horizontal = file.createIfcAlignmentHorizontal(GlobalId=ifcopenshell.guid.new())
+    with pytest.raises(ValueError):
+        ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal)
+
+
+def test_returns_none():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    result = ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal)
+
+    assert result is None
+
+
+def test_no_referents_or_rel_nests_created():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    referents_before = len(file.by_type("IfcReferent"))
+    rel_nests_before = len(file.by_type("IfcRelNests"))
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal)
+
+    assert len(file.by_type("IfcReferent")) == referents_before
+    assert len(file.by_type("IfcRelNests")) == rel_nests_before
+
+
+def test_no_real_segments_leaves_tags_none():
+    file = _new_file_no_context()
+    alignment = ifcopenshell.api.alignment.create(file, "A1", include_geometry=False)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    result = ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal)
+
+    assert result is None
+    segments = ifcopenshell.api.alignment.get_layout_segments(horizontal)
+    assert len(segments) == 1  # only the auto zero-length segment
+    assert segments[0].DesignParameters.StartTag is None
+    assert segments[0].DesignParameters.EndTag is None
+
+
+def test_single_real_segment_produces_only_boundary_tags():
+    file = _new_file_no_context()
+    alignment = ifcopenshell.api.alignment.create(file, "A1", include_geometry=False)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    design_parameters = file.createIfcAlignmentHorizontalSegment(
+        StartTag=None,
+        EndTag=None,
+        StartPoint=file.createIfcCartesianPoint((0.0, 0.0)),
+        StartDirection=0.0,
+        StartRadiusOfCurvature=0.0,
+        EndRadiusOfCurvature=0.0,
+        SegmentLength=100.0,
+        GravityCenterLineHeight=None,
+        PredefinedType="LINE",
+    )
+    ifcopenshell.api.alignment.create_layout_segment(file, horizontal, design_parameters)
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal, label_end_tag=True)
+
+    segments = _real_segments(horizontal)
+    assert len(segments) == 1
+    dp = segments[0].DesignParameters
+    assert _label(dp.StartTag) == "P.O.B."
+    assert _label(dp.EndTag) == "P.O.E."
+
+
+def test_end_tag_not_labelled_by_default():
+    file = _new_file_no_context()
+    alignment = ifcopenshell.api.alignment.create(file, "A1", include_geometry=False)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    design_parameters = file.createIfcAlignmentHorizontalSegment(
+        StartTag=None,
+        EndTag=None,
+        StartPoint=file.createIfcCartesianPoint((0.0, 0.0)),
+        StartDirection=0.0,
+        StartRadiusOfCurvature=0.0,
+        EndRadiusOfCurvature=0.0,
+        SegmentLength=100.0,
+        GravityCenterLineHeight=None,
+        PredefinedType="LINE",
+    )
+    ifcopenshell.api.alignment.create_layout_segment(file, horizontal, design_parameters)
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal)
+
+    segments = _real_segments(horizontal)
+    assert len(segments) == 1
+    dp = segments[0].DesignParameters
+    assert _label(dp.StartTag) == "P.O.B."
+    assert dp.EndTag is None
+
+
+def test_horizontal_tag_labels_and_adjacency():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal, label_end_tag=True)
+
+    segments = _real_segments(horizontal)
+    assert len(segments) == 7
+
+    start_labels = [_label(s.DesignParameters.StartTag) for s in segments]
+    end_labels = [_label(s.DesignParameters.EndTag) for s in segments]
+
+    assert start_labels == ["P.O.B.", "P.C.", "P.T.", "P.C.", "P.T.", "P.C.", "P.T."]
+    assert end_labels == ["P.C.", "P.T.", "P.C.", "P.T.", "P.C.", "P.T.", "P.O.E."]
+
+    # every real segment has both tags set
+    assert all(s.DesignParameters.StartTag is not None for s in segments)
+    assert all(s.DesignParameters.EndTag is not None for s in segments)
+
+    # adjacent segments agree on the tag describing their shared transition point
+    for i in range(len(segments) - 1):
+        assert segments[i].DesignParameters.EndTag == segments[i + 1].DesignParameters.StartTag
+
+
+def test_vertical_tag_labels_and_adjacency():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    vertical = ifcopenshell.api.alignment.get_vertical_layout(alignment)
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, vertical, label_end_tag=True)
+
+    segments = _real_segments(vertical)
+    assert len(segments) == 9
+
+    start_labels = [_label(s.DesignParameters.StartTag) for s in segments]
+    end_labels = [_label(s.DesignParameters.EndTag) for s in segments]
+
+    assert start_labels == [
+        "V.P.O.B.",
+        "P.V.C.",
+        "P.V.T.",
+        "P.V.C.",
+        "P.V.T.",
+        "P.V.C.",
+        "P.V.T.",
+        "P.V.C.",
+        "P.V.T.",
+    ]
+    assert end_labels == [
+        "P.V.C.",
+        "P.V.T.",
+        "P.V.C.",
+        "P.V.T.",
+        "P.V.C.",
+        "P.V.T.",
+        "P.V.C.",
+        "P.V.T.",
+        "V.P.O.E.",
+    ]
+
+    assert all(s.DesignParameters.StartTag is not None for s in segments)
+    assert all(s.DesignParameters.EndTag is not None for s in segments)
+
+    for i in range(len(segments) - 1):
+        assert segments[i].DesignParameters.EndTag == segments[i + 1].DesignParameters.StartTag
+
+
+def test_cant_layout_boundary_tags():
+    file = _new_file_no_context()
+    alignment = ifcopenshell.api.alignment.create(file, "A1", include_cant=True, include_geometry=False)
+    cant = ifcopenshell.api.alignment.get_cant_layout(alignment)
+
+    dp1 = file.createIfcAlignmentCantSegment(
+        StartDistAlong=0.0,
+        HorizontalLength=100.0,
+        StartCantLeft=0.0,
+        EndCantLeft=0.0,
+        StartCantRight=0.0,
+        EndCantRight=0.0,
+        PredefinedType="CONSTANTCANT",
+    )
+    ifcopenshell.api.alignment.create_layout_segment(file, cant, dp1)
+
+    dp2 = file.createIfcAlignmentCantSegment(
+        StartDistAlong=100.0,
+        HorizontalLength=50.0,
+        StartCantLeft=0.0,
+        EndCantLeft=0.0,
+        StartCantRight=0.0,
+        EndCantRight=0.0,
+        PredefinedType="CONSTANTCANT",
+    )
+    ifcopenshell.api.alignment.create_layout_segment(file, cant, dp2)
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, cant, label_end_tag=True)
+
+    segments = _real_segments(cant)
+    assert _label(segments[0].DesignParameters.StartTag) == "C.P.O.B."
+    assert _label(segments[-1].DesignParameters.EndTag) == "C.P.O.E."
+    # CONSTANTCANT -> CONSTANTCANT is currently an unfilled "xx" placeholder in the cant lookup
+    # table (_get_segment_start_point_label.py) -- out of scope to fill in here.
+    assert _label(segments[0].DesignParameters.EndTag) == "xx"
+    assert _label(segments[-1].DesignParameters.StartTag) == "xx"
+
+
+def test_exact_tag_format():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    ifcopenshell.api.alignment.update_alignment_parameter_segment_tags(file, horizontal)
+
+    start_station = ifcopenshell.api.alignment.get_alignment_start_station(file, alignment)
+    segments = _real_segments(horizontal)
+    assert segments[0].DesignParameters.StartTag == (
+        f"{ifcopenshell.util.alignment.station_as_string(file, start_station)} (P.O.B.)"
+    )
+
+
+test_wrong_layout_type_raises_type_error()
+test_not_nested_under_alignment_raises_value_error()
+test_returns_none()
+test_no_referents_or_rel_nests_created()
+test_no_real_segments_leaves_tags_none()
+test_single_real_segment_produces_only_boundary_tags()
+test_end_tag_not_labelled_by_default()
+test_horizontal_tag_labels_and_adjacency()
+test_vertical_tag_labels_and_adjacency()
+test_cant_layout_boundary_tags()
+test_exact_tag_format()

src/ifcopenshell-python/test/api/alignment/test_update_key_point_referents.py

@@ -66,6 +66,10 @@ def _pset_station(referent):
     return ifcopenshell.util.element.get_pset(referent, name="Pset_Stationing", prop="Station")
 
 
+def _label(name):
+    return name.rsplit("(", 1)[1].rstrip(")")
+
+
 def test_wrong_layout_type_raises_type_error():
     file = _new_file()
     alignment = _build_alignment(file)
@@ -82,13 +86,13 @@ def test_default_rel_nests_created_when_none_provided():
     nest = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
 
     assert nest.is_a("IfcRelNests")
-    assert nest.RelatingObject == horizontal
+    assert nest.RelatingObject == alignment
     assert nest.id() != segment_nest.id()
     assert len(nest.RelatedObjects) == 8
     assert all(r.is_a("IfcReferent") for r in nest.RelatedObjects)
 
 
-def test_second_call_without_rel_nests_reuses_existing_nest():
+def test_second_call_without_rel_nests_creates_separate_nest():
     file = _new_file()
     alignment = _build_alignment(file)
     horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
@@ -97,18 +101,31 @@ def test_second_call_without_rel_nests_reuses_existing_nest():
     nest1 = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
     nest2 = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
 
-    assert nest1.id() == nest2.id()
-    assert len(nest2.RelatedObjects) == 16
+    assert nest1.id() != nest2.id()
+    assert len(nest1.RelatedObjects) == 8
+    assert len(nest2.RelatedObjects) == 8
     segment_count_after = len(ifcopenshell.api.alignment.get_alignment_segment_nest(horizontal).RelatedObjects)
     assert segment_count_after == segment_count_before
 
 
+def test_passing_previous_nest_back_in_accumulates():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    nest1 = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
+    nest2 = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal, rel_nests=nest1)
+
+    assert nest1.id() == nest2.id()
+    assert len(nest2.RelatedObjects) == 16
+
+
 def test_provided_rel_nests_is_used_as_is():
     file = _new_file()
     alignment = _build_alignment(file)
     horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
 
-    # the nest may live anywhere the caller chooses, e.g. hung off the parent IfcAlignment
+    # rel_nests.RelatingObject must be the IfcAlignment that nests `layout`
     rel_nests = file.createIfcRelNests(GlobalId=ifcopenshell.guid.new(), RelatingObject=alignment, RelatedObjects=())
 
     result = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal, rel_nests=rel_nests)
@@ -118,6 +135,17 @@ def test_provided_rel_nests_is_used_as_is():
     assert len(result.RelatedObjects) == 8
 
 
+def test_provided_rel_nests_with_wrong_relating_object_raises_type_error():
+    file = _new_file()
+    alignment = _build_alignment(file)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+
+    rel_nests = file.createIfcRelNests(GlobalId=ifcopenshell.guid.new(), RelatingObject=horizontal, RelatedObjects=())
+
+    with pytest.raises(TypeError):
+        ifcopenshell.api.alignment.update_key_point_referents(file, horizontal, rel_nests=rel_nests)
+
+
 def test_clear_true_removes_old_referents_and_psets():
     file = _new_file()
     alignment = _build_alignment(file)
@@ -157,7 +185,7 @@ def test_default_horizontal_labels_and_order():
     nest = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
 
     expected = ["P.O.B.", "P.C.", "P.T.", "P.C.", "P.T.", "P.C.", "P.T.", "P.O.E."]
-    assert [r.Name.split(" (")[0] for r in nest.RelatedObjects] == expected
+    assert [_label(r.Name) for r in nest.RelatedObjects] == expected
 
     stations = [_pset_station(r) for r in nest.RelatedObjects]
     assert stations == sorted(stations)
@@ -183,7 +211,7 @@ def test_default_vertical_labels_and_order():
         "P.V.T.",
         "V.P.O.E.",
     ]
-    assert [r.Name.split(" (")[0] for r in nest.RelatedObjects] == expected
+    assert [_label(r.Name) for r in nest.RelatedObjects] == expected
 
     segments = ifcopenshell.api.alignment.get_layout_segments(vertical)
     real_segments = segments[:-1] if ifcopenshell.api.alignment.has_zero_length_segment(vertical) else segments
@@ -200,7 +228,7 @@ def test_name_format():
     nest = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
     referent = nest.RelatedObjects[0]
     station = _pset_station(referent)
-    assert referent.Name == f"P.O.B. ({ifcopenshell.util.alignment.station_as_string(file, station)})"
+    assert referent.Name == f"{alignment.Name} {ifcopenshell.util.alignment.station_as_string(file, station)} (P.O.B.)"
 
 
 def test_geometric_placement_when_layout_has_representation():
@@ -268,7 +296,7 @@ def test_cant_layout_boundary_labels():
 
     nest = ifcopenshell.api.alignment.update_key_point_referents(file, cant)
 
-    labels = [r.Name.split(" (")[0] for r in nest.RelatedObjects]
+    labels = [_label(r.Name) for r in nest.RelatedObjects]
     assert labels[0] == "C.P.O.B."
     assert labels[-1] == "C.P.O.E."
     # CONSTANTCANT -> CONSTANTCANT is currently an unfilled "xx" placeholder in the cant lookup
@@ -307,7 +335,7 @@ def test_single_real_segment_produces_only_boundary_labels():
     ifcopenshell.api.alignment.create_layout_segment(file, horizontal, design_parameters)
 
     nest = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
-    labels = [r.Name.split(" (")[0] for r in nest.RelatedObjects]
+    labels = [_label(r.Name) for r in nest.RelatedObjects]
     assert labels == ["P.O.B.", "P.O.E."]
 
 
@@ -345,6 +373,41 @@ def test_start_station_composes_for_child_alignment():
     assert stations == pytest.approx([100.0, 600.0, 900.0])
 
 
+def test_rel_nests_from_ancestor_used_for_naming_and_nesting():
+    """A vertical layout living under a child alignment (once a second vertical layout is
+    added, per CT 4.1.4.4.1.2) can still have its key-point referents named after and nested
+    to an ancestor alignment's own rel_nests -- e.g. the same one already holding that
+    ancestor's horizontal key points -- rather than the child's generic "Child of X" name."""
+    file = _new_file()
+    alignment = ifcopenshell.api.alignment.create(file, "A1", include_vertical=False, start_station=100.0)
+    horizontal = ifcopenshell.api.alignment.get_horizontal_layout(alignment)
+    horizontal_nest = ifcopenshell.api.alignment.update_key_point_referents(file, horizontal)
+    horizontal_count = len(horizontal_nest.RelatedObjects)
+
+    ifcopenshell.api.alignment.add_vertical_layout(file, alignment)
+    ifcopenshell.api.alignment.add_vertical_layout(file, alignment)  # forces the child-alignment split
+    child_alignment = alignment.IsDecomposedBy[0].RelatedObjects[-1]
+    child_vertical = ifcopenshell.api.alignment.get_vertical_layout(child_alignment)
+
+    dp = file.createIfcAlignmentVerticalSegment(
+        StartDistAlong=0.0,
+        HorizontalLength=500.0,
+        StartHeight=10.0,
+        StartGradient=0.01,
+        EndGradient=0.01,
+        PredefinedType="CONSTANTGRADIENT",
+    )
+    ifcopenshell.api.alignment.create_layout_segment(file, child_vertical, dp)
+
+    result = ifcopenshell.api.alignment.update_key_point_referents(file, child_vertical, rel_nests=horizontal_nest)
+
+    assert result == horizontal_nest
+    assert result.RelatingObject == alignment
+    assert len(result.RelatedObjects) == horizontal_count + 2
+    assert all(r.Name.startswith("A1 ") for r in result.RelatedObjects)
+    assert not any("Child of" in r.Name for r in result.RelatedObjects)
+
+
 def test_returns_ifc_rel_nests():
     file = _new_file()
     alignment = _build_alignment(file)
@@ -356,8 +419,10 @@ def test_returns_ifc_rel_nests():
 
 test_wrong_layout_type_raises_type_error()
 test_default_rel_nests_created_when_none_provided()
-test_second_call_without_rel_nests_reuses_existing_nest()
+test_second_call_without_rel_nests_creates_separate_nest()
+test_passing_previous_nest_back_in_accumulates()
 test_provided_rel_nests_is_used_as_is()
+test_provided_rel_nests_with_wrong_relating_object_raises_type_error()
 test_clear_true_removes_old_referents_and_psets()
 test_clear_false_appends_without_dedup()
 test_default_horizontal_labels_and_order()
@@ -369,4 +434,5 @@ test_cant_layout_boundary_labels()
 test_no_real_segments_produces_no_referents()
 test_single_real_segment_produces_only_boundary_labels()
 test_start_station_composes_for_child_alignment()
+test_rel_nests_from_ancestor_used_for_naming_and_nesting()
 test_returns_ifc_rel_nests()

src/ifcopenshell-python/test/api/sequence/test_create_baseline.py

@@ -0,0 +1,146 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2026 IfcOpenShell contributors
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+
+import pytest
+
+import ifcopenshell.api.root
+import ifcopenshell.api.sequence
+import ifcopenshell.util.sequence
+import test.bootstrap
+
+
+class TestCreateBaseline(test.bootstrap.IFC4):
+    def create_planned_schedule(self, name="Design & Build"):
+        ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcProject")
+        return ifcopenshell.api.sequence.add_work_schedule(self.file, name=name, predefined_type="PLANNED")
+
+    def test_returns_the_created_baseline_schedule(self):
+        planned = self.create_planned_schedule()
+        root_task = ifcopenshell.api.sequence.add_task(self.file, work_schedule=planned, name="Design")
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        assert baseline.is_a("IfcWorkSchedule")
+        assert baseline.Name == "Baseline 1"
+        assert baseline.PredefinedType == "BASELINE"
+        baseline_roots = ifcopenshell.util.sequence.get_root_tasks(baseline)
+        assert [task.Name for task in baseline_roots] == [root_task.Name]
+        assert baseline_roots != [root_task]
+
+    def test_falls_back_to_the_planned_schedule_name(self):
+        planned = self.create_planned_schedule()
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned)
+
+        assert baseline.Name == "Design & Build"
+
+    def test_leaves_the_name_null_when_both_names_are_omitted(self):
+        planned = self.create_planned_schedule()
+        planned.Name = None
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned)
+
+        assert baseline.Name is None
+
+    def test_rejects_a_non_planned_schedule(self):
+        ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcProject")
+        actual = ifcopenshell.api.sequence.add_work_schedule(self.file, predefined_type="ACTUAL")
+
+        with pytest.raises(ValueError):
+            ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=actual)
+
+    def test_baselines_a_schedule_without_tasks(self):
+        planned = self.create_planned_schedule()
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        assert ifcopenshell.util.sequence.get_root_tasks(baseline) == []
+
+    def test_baselines_every_root_task(self):
+        planned = self.create_planned_schedule()
+        ifcopenshell.api.sequence.add_task(self.file, work_schedule=planned, name="Design")
+        ifcopenshell.api.sequence.add_task(self.file, work_schedule=planned, name="Construction")
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        baseline_roots = ifcopenshell.util.sequence.get_root_tasks(baseline)
+        assert sorted(task.Name for task in baseline_roots) == ["Construction", "Design"]
+
+    def test_baselines_nested_tasks(self):
+        planned = self.create_planned_schedule()
+        root_task = ifcopenshell.api.sequence.add_task(self.file, work_schedule=planned, name="Construction")
+        ifcopenshell.api.sequence.add_task(self.file, parent_task=root_task, name="Foundations")
+        ifcopenshell.api.sequence.add_task(self.file, parent_task=root_task, name="Superstructure")
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        baseline_root = ifcopenshell.util.sequence.get_root_tasks(baseline)[0]
+        nested = ifcopenshell.util.sequence.get_nested_tasks(baseline_root)
+        assert sorted(task.Name for task in nested) == ["Foundations", "Superstructure"]
+        assert len(self.file.by_type("IfcTask")) == 6
+
+    def test_baselines_task_attributes_and_times(self):
+        planned = self.create_planned_schedule()
+        task = ifcopenshell.api.sequence.add_task(
+            self.file, work_schedule=planned, name="Foundations", identification="A1", description="Pour concrete"
+        )
+        ifcopenshell.api.sequence.add_task_time(self.file, task=task)
+        ifcopenshell.api.sequence.edit_task_time(
+            self.file, task_time=task.TaskTime, attributes={"ScheduleDuration": "P5D"}
+        )
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        baseline_task = ifcopenshell.util.sequence.get_root_tasks(baseline)[0]
+        assert baseline_task.Identification == "A1"
+        assert baseline_task.Description == "Pour concrete"
+        assert baseline_task.TaskTime != task.TaskTime
+        assert baseline_task.TaskTime.ScheduleDuration == "P5D"
+
+    def test_baselines_sequence_relationships_between_tasks(self):
+        planned = self.create_planned_schedule()
+        root_task = ifcopenshell.api.sequence.add_task(self.file, work_schedule=planned, name="Construction")
+        predecessor = ifcopenshell.api.sequence.add_task(self.file, parent_task=root_task, name="Foundations")
+        successor = ifcopenshell.api.sequence.add_task(self.file, parent_task=root_task, name="Superstructure")
+        ifcopenshell.api.sequence.assign_sequence(self.file, relating_process=predecessor, related_process=successor)
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        baseline_root = ifcopenshell.util.sequence.get_root_tasks(baseline)[0]
+        nested = {task.Name: task for task in ifcopenshell.util.sequence.get_nested_tasks(baseline_root)}
+        rels = nested["Foundations"].IsPredecessorTo
+        assert len(rels) == 1
+        assert rels[0].RelatedProcess == nested["Superstructure"]
+
+    def test_references_the_planned_schedule_and_tasks(self):
+        planned = self.create_planned_schedule()
+        root_task = ifcopenshell.api.sequence.add_task(self.file, work_schedule=planned, name="Construction")
+        subtask = ifcopenshell.api.sequence.add_task(self.file, parent_task=root_task, name="Foundations")
+
+        baseline = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+
+        baseline_root = ifcopenshell.util.sequence.get_root_tasks(baseline)[0]
+        baseline_subtask = ifcopenshell.util.sequence.get_nested_tasks(baseline_root)[0]
+        references = {
+            rel.RelatingObject: list(rel.RelatedObjects) for rel in self.file.by_type("IfcRelDefinesByObject")
+        }
+        assert references[planned] == [baseline]
+        assert references[root_task] == [baseline_root]
+        assert references[subtask] == [baseline_subtask]
+
+    def test_reuses_the_existing_reference_for_further_baselines(self):
+        planned = self.create_planned_schedule()
+
+        first = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 1")
+        second = ifcopenshell.api.sequence.create_baseline(self.file, work_schedule=planned, name="Baseline 2")
+
+        assert len(planned.Declares) == 1
+        assert list(planned.Declares[0].RelatedObjects) == [first, second]

src/ifcopenshell-python/test/util/test_alignment.py

@@ -77,10 +77,72 @@ def _test_us_stations():
     assert s == "-1234+56.79"
 
 
+def _test_custom_named_conversion_based_unit_stations():
+    """Regression test: station_as_string() must work for an
+    IfcConversionBasedUnit whose Name isn't one of the fixed set
+    ifcopenshell.util.unit.si_conversions recognises (e.g. a project that,
+    reasonably, names its foot-based unit something other than the bare
+    "foot" IfcOpenShell's own add_conversion_based_unit() produces -- for
+    instance to distinguish the US survey foot, 1200/3937 m exactly, from
+    the international foot, 0.3048 m exactly, which differ by ~2 ppm and
+    are NOT interchangeable once a project is tied to a US state plane CRS,
+    virtually all of which are defined in US survey feet).
+
+    Previously, station_as_string() converted via
+    ifcopenshell.util.unit.convert(), which looks up the conversion factor
+    BY NAME in si_conversions -- silently substituting a factor of 1.0
+    (i.e. treating the value as if it were already in the display unit) for
+    any unrecognised name, rather than raising an error. For a project unit
+    like "US survey foot" this inflated every station string by the
+    project-unit<->metre ratio (~3.28x), even though the underlying
+    Pset_Stationing.Station numeric value written by
+    ifcopenshell.api.alignment.create()/update_key_point_referents was
+    correct throughout -- only the display text was wrong.
+    """
+    file = ifcopenshell.file(schema="IFC4X3_ADD2")
+    project = file.createIfcProject(GlobalId=ifcopenshell.guid.new(), Name="Test")
+
+    # Hand-built rather than via add_conversion_based_unit(), since that
+    # API also resolves its conversion factor by name (si_conversions) and
+    # can't produce a custom name paired with a specific factor.
+    si_unit = file.createIfcSIUnit(UnitType="LENGTHUNIT", Name="METRE")
+    value_component = file.create_entity("IfcReal", wrappedValue=1200.0 / 3937.0)  # US survey foot, exact
+    conversion_factor = file.createIfcMeasureWithUnit(value_component, si_unit)
+    exponents = file.createIfcDimensionalExponents(1, 0, 0, 0, 0, 0, 0)
+    length = file.createIfcConversionBasedUnit(exponents, "LENGTHUNIT", "US survey foot", conversion_factor)
+    ifcopenshell.api.unit.assign_unit(file, units=[length])
+
+    # US survey foot and international foot differ by ~2 ppm. At small
+    # station values that's invisible at 2-decimal-place precision, so
+    # these match _test_us_stations()'s "foot" case exactly.
+    s = sta.station_as_string(file, 0.0)
+    assert s == "0+00.00"
+
+    s = sta.station_as_string(file, 100.00)
+    assert s == "1+00.00"
+
+    s = sta.station_as_string(file, -100.00)
+    assert s == "-1+00.00"
+
+    # At a large enough station, ~2 ppm DOES become visible at 2 decimal
+    # places (123456.789 * 2e-6 =~ 0.25) -- this is the real, correct US
+    # survey foot vs. international foot difference, not a bug. Before the
+    # fix, the name-based lookup's silent 1.0 fallback inflated this same
+    # input by ~3.28x to "1234+57.036" -> "4050+82.90"-ish territory, wildly
+    # different from either correct answer -- so this still exercises the
+    # regression, it's just not identical to the "foot" case's value.
+    s = sta.station_as_string(file, 123456.789)
+    assert s == "1234+57.04"
+
+    s = sta.station_as_string(file, -123456.789)
+    assert s == "-1234+57.04"
+
+
 def test_station_as_string():
     _test_si_stations()
     _test_si_stations_millimeter()
     _test_us_stations()
+    _test_custom_named_conversion_based_unit_stations()
 
 
 test_station_as_string()

src/ifcopenshell-python/test/util/test_unit.py

@@ -200,6 +200,31 @@ class TestCalculateUnitScale(test.bootstrap.IFC4):
         ifcopenshell.api.unit.assign_unit(self.file, units=[angle])
         assert subject.calculate_unit_scale(self.file, "PLANEANGLEUNIT") == pi / 180 * 0.001
 
+    def test_prefix_is_raised_to_the_length_exponent_for_area_and_volume(self):
+        # A prefixed square/cubic metre is (prefix-metre) squared/cubed:
+        # DECI SQUARE_METRE = dm2 = 1e-2 m2, DECI CUBIC_METRE = dm3 (litre) = 1e-3 m3.
+        # https://github.com/IfcOpenShell/IfcOpenShell/issues/9278
+        ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcProject")
+        area = ifcopenshell.api.unit.add_si_unit(self.file, unit_type="AREAUNIT")
+        area.Prefix = "DECI"
+        volume = ifcopenshell.api.unit.add_si_unit(self.file, unit_type="VOLUMEUNIT")
+        volume.Prefix = "DECI"
+        ifcopenshell.api.unit.assign_unit(self.file, units=[area, volume])
+        assert subject.calculate_unit_scale(self.file, "AREAUNIT") == pytest.approx(0.1**2)
+        assert subject.calculate_unit_scale(self.file, "VOLUMEUNIT") == pytest.approx(0.1**3)
+
+    def test_prefix_stays_linear_for_units_that_are_not_a_pure_power_of_length(self):
+        # For derived and non-length SI units the prefix scales the unit itself:
+        # KILO PASCAL = 1e3 Pa, KILO GRAM = 1e3 g.
+        ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcProject")
+        pressure = ifcopenshell.api.unit.add_si_unit(self.file, unit_type="PRESSUREUNIT")
+        pressure.Prefix = "KILO"
+        mass = ifcopenshell.api.unit.add_si_unit(self.file, unit_type="MASSUNIT")
+        mass.Prefix = "KILO"
+        ifcopenshell.api.unit.assign_unit(self.file, units=[pressure, mass])
+        assert subject.calculate_unit_scale(self.file, "PRESSUREUNIT") == pytest.approx(1000)
+        assert subject.calculate_unit_scale(self.file, "MASSUNIT") == pytest.approx(1000)
+
 
 class TestFormatLength(test.bootstrap.IFC4):
     def test_run(self):