Updates alignment api. Fixes bugs authoring semantic-only alignment

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

@@ -0,0 +1,51 @@
+# 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/>.
+
+from collections.abc import Sequence
+
+from ifcopenshell import entity_instance
+
+import ifcopenshell.api.alignment
+
+from ifcopenshell.api.alignment.get_mapped_segments import _get_curve_segment_count
+
+
+def get_curve_segment(layout: entity_instance, segment: entity_instance) -> entity_instance:
+    """
+    Returns the IfcCurveSegment associated with the given alignment segment. If the curve segment does not exist, None is returned.
+
+    Example:
+
+    .. code:: python
+
+        horizontal = model.by_type("IfcAlignmentHorizontal")[0]
+        curve_segment = ifcopenshell.api.alignment.get_curve_segment(horizontal, alignment_segment)
+    """
+    index = 0
+    segment_nest = ifcopenshell.api.alignment.get_alignment_segment_nest(layout)
+    for related_object in segment_nest.RelatedObjects:
+        if related_object == segment:
+            break
+        n = _get_curve_segment_count(related_object)
+        index += n
+
+    curve = ifcopenshell.api.alignment.get_layout_curve(layout)
+    if curve and index < len(curve.Segments):
+        return curve.Segments[index]
+    else:
+        return None