From 647e379c69b4ee5d0e0ecd1c44f3863e7e6b2463 Mon Sep 17 00:00:00 2001
From: Richard Brice <37087370+RickBrice@users.noreply.github.com>
Date: Sun, 20 Oct 2024 08:19:49 -0700
Subject: [PATCH] Fixes problem with evaluating point on vertical alignment

Fixes evaluation of IfcLine parent curve for IfcGradientCurve. See https://github.com/IfcOpenShell/IfcOpenShell/discussions/5587
---
 src/ifcgeom/mapping/IfcCurveSegment.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/ifcgeom/mapping/IfcCurveSegment.cpp b/src/ifcgeom/mapping/IfcCurveSegment.cpp
index 151360392d..5f7acec538 100644
--- a/src/ifcgeom/mapping/IfcCurveSegment.cpp
+++ b/src/ifcgeom/mapping/IfcCurveSegment.cpp
@@ -696,6 +696,14 @@ class curve_segment_evaluator {
        auto pcDx = dr[0];
        auto pcDy = dr[1];
 
+       if (segment_type_ == ST_VERTICAL && placement_) {
+          // the general algorithm for mapping parent curve onto curve segment doesn't
+          // exactly work for IfcLine. This is easily overcome by usnig the curve segment
+          // placement for the IfcLine direction
+          pcDx = (*placement_)(0, 0);
+          pcDy = (*placement_)(1, 0);
+       }
+
        if (segment_type_ == ST_HORIZONTAL || segment_type_ == ST_VERTICAL || segment_type_ == ST_CANT) {
           std::function<double(double)> convert_u;
           if (segment_type_ == ST_HORIZONTAL || segment_type_ == ST_CANT) {