From c93704f097625b518731e7d4d8ded06c5ef7c779 Mon Sep 17 00:00:00 2001
From: Richard Brice <37087370+RickBrice@users.noreply.github.com>
Date: Thu, 2 May 2024 16:00:59 -0700
Subject: [PATCH] Fixes problem with IfcCurveSegment.Placement direction for
 parabolic vertical curves

---
 src/examples/IfcAlignment.cpp       | 2 +-
 src/ifcparse/IfcAlignmentHelper.cpp | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/examples/IfcAlignment.cpp b/src/examples/IfcAlignment.cpp
index f9ece6d5cb..a80ca10c97 100644
--- a/src/examples/IfcAlignment.cpp
+++ b/src/examples/IfcAlignment.cpp
@@ -163,7 +163,7 @@ std::pair<typename Schema::IfcCurveSegment*, typename Schema::IfcAlignmentSegmen
 
     auto curve_segment = new Schema::IfcCurveSegment(
         Schema::IfcTransitionCode::IfcTransitionCode_CONTSAMEGRADIENT,
-        new Schema::IfcAxis2Placement2D(p, new Schema::IfcDirection(std::vector<double>{1.0, 0.0})),
+        new Schema::IfcAxis2Placement2D(p, new Schema::IfcDirection(std::vector<double>{sqrt(1 - start_slope * start_slope), start_slope})),
         new Schema::IfcLengthMeasure(0.0),
         new Schema::IfcLengthMeasure(length),
         parent_curve);
diff --git a/src/ifcparse/IfcAlignmentHelper.cpp b/src/ifcparse/IfcAlignmentHelper.cpp
index 0e73b1cadf..08e17043b3 100644
--- a/src/ifcparse/IfcAlignmentHelper.cpp
+++ b/src/ifcparse/IfcAlignmentHelper.cpp
@@ -708,7 +708,7 @@ std::pair<Ifc4x3_add2::IfcCurveSegment*, Ifc4x3_add2::IfcCurveSegment*> mapAlign
 
         auto curve_segment = new Ifc4x3_add2::IfcCurveSegment(
             Ifc4x3_add2::IfcTransitionCode::IfcTransitionCode_CONTSAMEGRADIENT,
-            new Ifc4x3_add2::IfcAxis2Placement2D(new Ifc4x3_add2::IfcCartesianPoint({start_distance_along,start_height}), new Ifc4x3_add2::IfcDirection({1.0, 0.0})),
+            new Ifc4x3_add2::IfcAxis2Placement2D(new Ifc4x3_add2::IfcCartesianPoint({start_distance_along, start_height}), new Ifc4x3_add2::IfcDirection({sqrt(1.0 - start_gradient * start_gradient), start_gradient})),
             new Ifc4x3_add2::IfcLengthMeasure(0.0),
             new Ifc4x3_add2::IfcLengthMeasure(horizontal_length),
             parent_curve);