From 924e337c9037eb3e467317b8a2882c3e3b664edb Mon Sep 17 00:00:00 2001
From: Dion Moult <dion@thinkmoult.com>
Date: Thu, 28 Mar 2024 16:56:54 +1100
Subject: [PATCH] Don't consider borderline points to be inside a shape for
 more robust protrusion results

---
 src/ifcgeom_schema_agnostic/IfcGeomTree.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/ifcgeom_schema_agnostic/IfcGeomTree.h b/src/ifcgeom_schema_agnostic/IfcGeomTree.h
index 3928d3e7c1..c72da5e59f 100644
--- a/src/ifcgeom_schema_agnostic/IfcGeomTree.h
+++ b/src/ifcgeom_schema_agnostic/IfcGeomTree.h
@@ -251,6 +251,10 @@ namespace IfcGeom {
                             */
                             double at, au, av;
                             if (intersectRayTriangle(ray_origin, ray_vector, ta, tb, tc, at, au, av, false)) {
+                                if (std::abs(at) < 1e-4) {
+                                    // The point is basically lying on a face so inside/outside is ambiguous.
+                                    return false;
+                                }
                                 // At is a signed intersection distance (positive is along +ray_vector)
                                 if (at > -1e-5) {
                                     total_intersections++;