Separates referent and alignment layout usages into different referents

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

@@ -60,6 +60,8 @@ from .create_segment_representations import create_segment_representations
 from .create_representation import create_representation
 from .distance_along_from_station import distance_along_from_station
 from .get_alignment import get_alignment
+from .get_alignment_layout_nest import get_alignment_layout_nest
+from .get_alignment_segment_nest import get_alignment_segment_nest
 from .get_alignment_station import get_alignment_station
 from .get_curve_segment_transition_code import get_curve_segment_transition_code
 from .get_layout_segments import get_layout_segments
@@ -74,6 +76,7 @@ from .get_curve import get_curve
 from .get_layout_curve import get_layout_curve
 from .get_mapped_segments import get_mapped_segments
 from .get_parent_alignment import get_parent_alignment
+from .get_referent_nest import get_referent_nest
 from .has_zero_length_segment import has_zero_length_segment
 from .layout_horizontal_alignment_by_pi_method import layout_horizontal_alignment_by_pi_method
 from .layout_vertical_alignment_by_pi_method import layout_vertical_alignment_by_pi_method
@@ -97,7 +100,9 @@ __all__ = [
     "create_segment_representations",
     "distance_along_from_station",
     "get_alignment",
+    "get_alignment_layout_nest",
     "get_alignment_layouts",
+    "get_alignment_segment_nest",
     "get_alignment_station",
     "get_axis_subcontext",
     "get_basis_curve",
@@ -109,6 +114,7 @@ __all__ = [
     "get_layout_curve",
     "get_layout_segments",
     "get_parent_alignment",
+    "get_referent_nest",
     "get_vertical_layout",
     "has_zero_length_segment",
     "layout_horizontal_alignment_by_pi_method",

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

@@ -173,7 +173,8 @@ def _add_segment_to_layout(file: ifcopenshell.file, layout: entity_instance, seg
 
         # get the previous segment. Working from the end of the basis curve, -1 is zero length segment
         # -2 is the newly added segment, so -3 is the segment occuring just before the newly added segment
-        prev_segment = layout.IsNestedBy[0].RelatedObjects[-3] if 2 < len(layout.IsNestedBy[0].RelatedObjects) else None
+        segment_nest = ifcopenshell.api.alignment.get_alignment_segment_nest(layout)
+        prev_segment = segment_nest.RelatedObjects[-3] if 2 < len(segment_nest.RelatedObjects) else None
         name = f"{_get_segment_start_point_label(prev_segment,segment)} ({ifcopenshell.util.alignment.station_as_string(file,station)})"
         referent = ifcopenshell.api.alignment.add_stationing_referent(
             file, segment, distance_along=dist_along, station=station, name=name
@@ -183,7 +184,8 @@ def _add_segment_to_layout(file: ifcopenshell.file, layout: entity_instance, seg
             # this is the first real segment in the horizontal alignment
             # update the location of the alignment's stationing referent
             alignment = ifcopenshell.api.alignment.get_alignment(layout)
-            stationing_referent = alignment.IsNestedBy[0].RelatedObjects[0]
+            ref_nest = ifcopenshell.api.alignment.get_referent_nest(file,alignment)
+            stationing_referent = ref_nest.RelatedObjects[0]
             p = curve_evaluator.evaluate(
                 stationing_referent.ObjectPlacement.RelativePlacement.Location.DistanceAlong.wrappedValue
             )

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

@@ -133,7 +133,9 @@ def add_stationing_referent(
     )
     pset_stationing = ifcopenshell.api.pset.add_pset(file, product=referent, name="Pset_Stationing")
     ifcopenshell.api.pset.edit_pset(file, pset=pset_stationing, properties={"Station": station})
-    ifcopenshell.api.nest.assign_object(file, related_objects=[referent], relating_object=element)
+
+    nest = ifcopenshell.api.alignment.get_referent_nest(file,element)
+    nest.RelatedObjects += (referent,)
 
     if len(alignment.Positions) == 0:
         rel_positions = file.createIfcRelPositions(

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

@@ -87,7 +87,6 @@ def create(
         # define stationing
         name = ifcopenshell.util.alignment.station_as_string(file, start_station)
         referent = ifcopenshell.api.alignment.add_stationing_referent(file, alignment, 0.0, start_station, name)
-        ifcopenshell.api.nest.reorder_nesting(file, referent, -1, 0)
 
 
     # IFC 4.1.4.1.1 Alignment Aggregation To Project

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

@@ -16,16 +16,16 @@
 # 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
 from ifcopenshell import entity_instance
-from collections.abc import Sequence
-
-import ifcopenshell.util.representation
-
 
 def get_alignment(layout: entity_instance) -> entity_instance:
     """
     Returns the alignment that nests this layout
     """
-    return layout.Nests[0].RelatingObject if 0 < len(layout.Nests) else None
+    alignment = None
+    for nest in layout.Nests:
+        if nest.RelatingObject.is_a("IfcAlignment"):
+            alignment = nest.RelatingObject
+            break
+
+    return alignment

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

@@ -0,0 +1,36 @@
+# 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
+from ifcopenshell import entity_instance
+
+def get_alignment_layout_nest(alignment: entity_instance) -> entity_instance:
+    """
+    Searches for the IfcRelNest that contains IfcAlignmentHorizontal, IfcAlignmentVertical, or IfcAlignmentCant
+
+    :param alignment: the alignment 
+    :return: Returns the IfcRelNests containing the alignment layout
+    """
+    layout_types = ["IfcAlignmentHorizontal", "IfcAlignmentVertical", "IfcAlignmentCant"]
+
+    for nest in alignment.IsNestedBy:
+        for related_object in nest.RelatedObjects:
+            if related_object.is_a() in layout_types:
+                return nest
+
+    return None

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

@@ -0,0 +1,33 @@
+# 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
+from ifcopenshell import entity_instance
+
+def get_alignment_segment_nest(layout: entity_instance) -> entity_instance:
+    """
+    Searches for the IfcRelNest that contains IfcAlignmentSegment
+
+    :param layout: an alignment layout, expected to be one of IfcAlignmentHorizontal, IfcAlignmentVertical, or IfcAlignmentCant
+    :return: Returns the IfcRelNests
+    """
+    for nest in layout.IsNestedBy:
+        for related_object in nest.RelatedObjects:
+            if related_object.is_a("IfcAlignmentSegment"):
+                return nest
+    return None

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

@@ -0,0 +1,36 @@
+# 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
+from ifcopenshell import entity_instance
+
+def get_referent_nest(file: ifcopenshell.file,entity: entity_instance) -> entity_instance:
+    """
+    Searches for the IfcRelNest that contains IfcReferent. If one is not found, a empty IfcRelNests is created.
+
+    :param file:
+    :param entity: any entity that is the parent in a nesting relationship, but intended to be IfcAlignment, IfcAlignmentHorizontal, IfcAlignmentVertical, or IfcAlignmentCant
+    :return: Returns the IfcRelNests.
+    """
+    for nest in entity.IsNestedBy:
+        for related_object in nest.RelatedObjects:
+            if related_object.is_a("IfcReferent"):
+                return nest
+
+    nest = file.createIfcRelNests(GlobalId=ifcopenshell.guid.new(),RelatingObject=entity,RelatedObjects=[])
+    return nest