From 9e9d66451177950c7f78f52fcaaacecb871858e4 Mon Sep 17 00:00:00 2001
From: Thomas Krijnen <t.krijnen@gmail.com>
Date: Mon, 17 Nov 2025 18:25:51 +0100
Subject: [PATCH] .glb --separate-z-up-node option

---
 src/ifcgeom/ConversionSettings.h   |  2 +-
 src/ifcgeom/GeometrySerializer.h   |  9 ++++++--
 src/serializers/GltfSerializer.cpp | 36 +++++++++++++++++++-----------
 src/serializers/GltfSerializer.h   |  2 +-
 4 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/src/ifcgeom/ConversionSettings.h b/src/ifcgeom/ConversionSettings.h
index 720d25ba66..eb405a9e7c 100644
--- a/src/ifcgeom/ConversionSettings.h
+++ b/src/ifcgeom/ConversionSettings.h
@@ -647,7 +647,7 @@ namespace ifcopenshell {
 		};
 
 		class Settings : public SettingsContainer<
-                                          std::tuple<MesherLinearDeflection, MesherAngularDeflection, ReorientShells, LengthUnit, PlaneUnit, Precision, OutputDimensionality, LayersetFirst, DisableBooleanResult, NoWireIntersectionCheck, NoWireIntersectionTolerance, PrecisionFactor, DebugBooleanOperations, BooleanAttempt2d, SurfaceColour, WeldVertices, UseWorldCoords, UnifyShapes, UseMaterialNames, ConvertBackUnits, ContextIds, ContextTypes, ContextIdentifiers, IteratorOutput, DisableOpeningSubtractions, ApplyDefaultMaterials, DontEmitNormals, GenerateUvs, ApplyLayerSets, UseElementHierarchy, ValidateQuantities, EdgeArrows, BuildingLocalPlacement, SiteLocalPlacement, ForceSpaceTransparency, CircleSegments, CgalSmoothAngleDegrees, KeepBoundingBoxes, ComputeCurvature, FunctionStepType, FunctionStepParam, NoParallelMapping, PermissiveShapeReuse, ModelOffset, ModelRotation, TriangulationType, CgalEmitOriginalEdges, OcctNoCleanTriangulation, CacheShapes, DeferProcessingFirstElement, MaxOffset, MaxOffsetDeviation, ApplyOffset>
+                             std::tuple<MesherLinearDeflection, MesherAngularDeflection, ReorientShells, LengthUnit, PlaneUnit, Precision, OutputDimensionality, LayersetFirst, DisableBooleanResult, NoWireIntersectionCheck, NoWireIntersectionTolerance, PrecisionFactor, DebugBooleanOperations, BooleanAttempt2d, SurfaceColour, WeldVertices, UseWorldCoords, UnifyShapes, UseMaterialNames, ConvertBackUnits, ContextIds, ContextTypes, ContextIdentifiers, IteratorOutput, DisableOpeningSubtractions, ApplyDefaultMaterials, DontEmitNormals, GenerateUvs, ApplyLayerSets, UseElementHierarchy, ValidateQuantities, EdgeArrows, BuildingLocalPlacement, SiteLocalPlacement, ForceSpaceTransparency, CircleSegments, CgalSmoothAngleDegrees, KeepBoundingBoxes, ComputeCurvature, FunctionStepType, FunctionStepParam, NoParallelMapping, PermissiveShapeReuse, ModelOffset, ModelRotation, TriangulationType, CgalEmitOriginalEdges, OcctNoCleanTriangulation, CacheShapes, DeferProcessingFirstElement, MaxOffset, MaxOffsetDeviation, ApplyOffset>
 		>
 		{};
 }
diff --git a/src/ifcgeom/GeometrySerializer.h b/src/ifcgeom/GeometrySerializer.h
index deef2c59c2..d8d4605de5 100644
--- a/src/ifcgeom/GeometrySerializer.h
+++ b/src/ifcgeom/GeometrySerializer.h
@@ -87,12 +87,17 @@ inline namespace settings {
 		static constexpr const char* const description = "Use a geometrical section rather than full polyhedral output and footprint in TTL WKT";
 		static constexpr bool defaultvalue = false;
 	};
+
+	struct SeparateZUpNode : public SettingBase<SeparateZUpNode, bool> {
+        static constexpr const char* const name = "separate-z-up-node";
+        static constexpr const char* const description = "Introduce a separate Z-Up node into the GlTF hierarchy instead of multiplying the transform into the root node matrices";
+        static constexpr bool defaultvalue = false;
+    };
 }
 
 class SerializerSettings : public SettingsContainer <
 	// @todo should we use tuple_cat here to unify the settings into a single class?
-	std::tuple<UseElementNames, UseElementGuids, UseElementStepIds, UseElementTypes, UseYUp, WriteGltfEcef, FloatingPointDigits, BaseUri, WktUseSection>
->
+    std::tuple<UseElementNames, UseElementGuids, UseElementStepIds, UseElementTypes, UseYUp, WriteGltfEcef, FloatingPointDigits, BaseUri, WktUseSection, SeparateZUpNode>>
 {};
 
 }
diff --git a/src/serializers/GltfSerializer.cpp b/src/serializers/GltfSerializer.cpp
index 12627e0b39..3627106f42 100644
--- a/src/serializers/GltfSerializer.cpp
+++ b/src/serializers/GltfSerializer.cpp
@@ -215,7 +215,7 @@ void GltfSerializer::write(const IfcGeom::TriangulationElement* o) {
 			json parent_node = json::object();
 
 			std::array<double, 16> matrix_flat;
-			if (settings_.get<ifcopenshell::geometry::settings::WriteGltfEcef>().get() || !is_root) {
+            if (settings_.get<ifcopenshell::geometry::settings::SeparateZUpNode>().get() || settings_.get<ifcopenshell::geometry::settings::WriteGltfEcef>().get() || !is_root) {
 				// y-up transform is only accounted for on root
 				matrix_flat = {
 					mm(0,0), mm(1,0), mm(2,0), mm(3,0),
@@ -258,7 +258,7 @@ void GltfSerializer::write(const IfcGeom::TriangulationElement* o) {
 	json node;
     {
 		std::array<double, 16> matrix_flat;
-		if (settings_.get<ifcopenshell::geometry::settings::WriteGltfEcef>().get() || !o->parents().empty()) {
+        if (settings_.get<ifcopenshell::geometry::settings::SeparateZUpNode>().get() || settings_.get<ifcopenshell::geometry::settings::WriteGltfEcef>().get() || !o->parents().empty()) {
 			// y-up transform is only accounted for on root
 			matrix_flat = {
 				m(0,0), m(1,0), m(2,0), m(3,0),
@@ -411,20 +411,30 @@ void write_block(std::ostream& fs, It begin, It end) {
 }
 
 void GltfSerializer::finalize() {
+    // separate z up
+    if (settings_.get<ifcopenshell::geometry::settings::SeparateZUpNode>().get()) {
+        z_up_transform_ = json::object();
+        (*z_up_transform_)["name"] = "Z_UP";
+		static const std::array<double, 16> z_up_matrix = {
+			1, 0, 0, 0,
+			0, 0, -1, 0,
+			0, 1, 0, 0,
+			0, 0, 0, 1};
+        (*z_up_transform_)["matrix"] = z_up_matrix;
+        (*z_up_transform_)["children"] = roots_;
+        json_["nodes"].push_back(*z_up_transform_);
+    }
+
 	if (north_rotation_) {
-		(*north_rotation_)["children"] = json::array();
-		for (int i = 0; i < json_["nodes"].size(); ++i) {
-			(*north_rotation_)["children"].push_back(i);
-		}
-		json_["nodes"].push_back(*north_rotation_);
+        (*north_rotation_)["children"] = roots_;
 	}
 
 	if (ecef_transform_) {
-		(*ecef_transform_)["children"] = json::array();
-		for (int i = 0; i < json_["nodes"].size(); ++i) {
-			(*ecef_transform_)["children"].push_back(i);
-		}
-		json_["nodes"].push_back(*ecef_transform_);
+        (*ecef_transform_)["children"] = roots_;
+	}
+
+	if (z_up_transform_) {
+        (*ecef_transform_)["children"] = roots_;
 	}
 
 	tmp_fstream1_.close();
@@ -447,7 +457,7 @@ void GltfSerializer::finalize() {
 	json scene_0;
     if (geometry_settings().get<ifcopenshell::geometry::settings::UseElementHierarchy>().get()) {
         scene_0["nodes"] = roots_;
-    } else if (north_rotation_ || ecef_transform_) {
+    } else if (north_rotation_ || ecef_transform_ || z_up_transform_) {
 		scene_0["nodes"] = std::array<size_t, 1>{json_["nodes"].size() - 1};
 	} else {
 		scene_0["nodes"] = node_array_;
diff --git a/src/serializers/GltfSerializer.h b/src/serializers/GltfSerializer.h
index e08f2b55f1..d3754d90a0 100644
--- a/src/serializers/GltfSerializer.h
+++ b/src/serializers/GltfSerializer.h
@@ -36,7 +36,7 @@ private:
 	std::ofstream fstream_, tmp_fstream1_, tmp_fstream2_;
 	std::map<std::string, int> materials_, meshes_;
 	json json_, node_array_;
-	boost::optional<json> ecef_transform_, north_rotation_;
+	boost::optional<json> ecef_transform_, north_rotation_, z_up_transform_;
 	int bufferViewId;
     std::map<const IfcUtil::IfcBaseEntity*, size_t> node_indices_;
     std::vector<size_t> roots_;