Missing concept template or IfcAlignment documentation needs revision

[RickBrice]

Problem
The documentation for IfcAlignment, in the Concept usage section, refers to "Alignment Geometry - Reusing Horizontal Layout".

The Alignment Geometry - Reusing Horizontal Layout concept is not documented in 4.1.7.1.1

I do not know the intent, but my guess is "Alignment Geometry - Reusing Horizontal Layout" is unnecessary because several IfcGradientCurve can use the same IfcCompositeCurve as the BasisCurve and the "Alignment Geometry - Horizontal and Vertical" concept is sufficient. Same would be true for Horizontal, Vertical and Cant.

Solution(s)
Remove all references to Alignment Geometry - Reusing Horizontal Layout from the schema documentation.

Require schema changes?

• yes
• ✓ no
• don't know

Require documentation changes?

• ✓ yes
• no
• don't know

[aothms]

This is not in the alignment geometry sections, but alignment layout, and that also makes the intent more clear, a geometry definition can be fairly easily reused, but not the tree of segments.

https://standards.buildingsmart.org/IFC/RELEASE/IFC4_3/HTML/concepts/Object_Composition/Nesting/Alignment_Layouts/Alignment_Layout_-_Reusing_Horizontal_Layout/content.html

[RickBrice]

The text refers to both concepts when only one exists. Documentation clean-up in needed.

[civilx64]

I'm late to the discussion here but my understanding is that the concept of reusing horizontal alignment refers to the (very common) practice in industry of having multiple vertical layouts for a given horizontal layout. For example, one vertical layout would be a series of linear elements representing original ground as extracted from a survey surface. Another vertical layout would be the preferred vertical design. There may be multiple additional alternates for the design vertical layout as well. Then you start adding vertical layouts for the grading of ditches. These typically only run for a short station range along the alignment, so for a 5 mile roadway you might have 20-some ditch profiles on either side of the roadway. If you have a divided carriageway section with a center median then that potentially adds another 10-20 in the median. So accounting for all ditch profiles left, right, and center, plus existing ground, plus multiple design alternates, you're looking at 50+ vertical layouts for a single horizontal layout.