You can now specify custom project norths when loading in models in absolute terms

src/blenderbim/blenderbim/bim/import_ifc.py

@@ -1498,6 +1498,7 @@ class IfcImportSettings:
         self.distance_limit = 1000
         self.false_origin_mode = "AUTOMATIC"
         self.false_origin = None
+        self.project_north = None
         self.element_offset = 0
         self.element_limit = 30000
         self.has_filter = None
@@ -1533,6 +1534,10 @@ class IfcImportSettings:
             settings.false_origin = [float(o) for o in props.false_origin.split(",")[:3]]
         except:
             settings.false_origin = [0, 0, 0]
+        try:
+            settings.project_north = float(props.project_north)
+        except:
+            settings.project_north = 0
         settings.element_offset = props.element_offset
         settings.element_limit = props.element_limit
         return settings

src/blenderbim/blenderbim/bim/module/georeference/data.py

@@ -35,7 +35,6 @@ class GeoreferenceData:
     @classmethod
     def load(cls):
         cls.data["coordinate_operation_class"] = cls.coordinate_operation_class()
-        cls.data["blender_derived_angle"] = cls.blender_derived_angle()
         cls.data["coordinate_operation"] = cls.coordinate_operation()
         cls.data["map_derived_angle"] = cls.map_derived_angle()
         cls.data["projected_crs"] = cls.projected_crs()
@@ -56,19 +55,6 @@ class GeoreferenceData:
         version = tool.Ifc.get_schema()
         return [(c, c, get_entity_doc(version, c).get("description", "")) for c in sorted(names)]
 
-    @classmethod
-    def blender_derived_angle(cls):
-        props = bpy.context.scene.BIMGeoreferenceProperties
-        if props.has_blender_offset:
-            return str(
-                round(
-                    ifcopenshell.util.geolocation.xaxis2angle(
-                        float(props.blender_x_axis_abscissa), float(props.blender_x_axis_ordinate)
-                    ),
-                    3,
-                )
-            )
-
     @classmethod
     def coordinate_operation(cls):
         if tool.Ifc.get_schema() == "IFC2X3":

src/blenderbim/blenderbim/bim/module/georeference/prop.py

@@ -119,11 +119,12 @@ class BIMGeoreferenceProperties(PropertyGroup):
     blender_eastings: StringProperty(name="Blender Eastings", default="0")
     blender_northings: StringProperty(name="Blender Northings", default="0")
     blender_orthogonal_height: StringProperty(name="Blender Orthogonal Height", default="0")
-    blender_x_axis_abscissa: StringProperty(name="Blender X Axis Abscissa", default="1")
-    blender_x_axis_ordinate: StringProperty(name="Blender X Axis Ordinate", default="0")
+    blender_project_north: StringProperty(name="Blender Angle to Grid North", default="0")
     blender_offset_x: StringProperty(name="Blender Offset X", default="0")
     blender_offset_y: StringProperty(name="Blender Offset Y", default="0")
     blender_offset_z: StringProperty(name="Blender Offset Z", default="0")
+    blender_x_axis_abscissa: StringProperty(name="Blender X Axis Abscissa", default="1")
+    blender_x_axis_ordinate: StringProperty(name="Blender X Axis Ordinate", default="0")
     true_north_angle: StringProperty(name="True North Angle", update=update_true_north_angle)
     true_north_abscissa: StringProperty(name="True North Abscissa", update=update_true_north_vector)
     true_north_ordinate: StringProperty(name="True North Ordinate", update=update_true_north_vector)

src/blenderbim/blenderbim/bim/module/georeference/ui.py

@@ -92,7 +92,7 @@ class BIM_PT_gis(Panel):
 
         if props.has_blender_offset:
             row = self.layout.row()
-            row.label(text="Blender Session Origin", icon="TRACKING_REFINE_FORWARDS")
+            row.label(text="Blender Session Coordinates", icon="TRACKING_REFINE_FORWARDS")
 
             row = self.layout.row(align=True)
             row.label(text=f"Eastings ({GeoreferenceData.data['local_unit_symbol']})")
@@ -104,14 +104,8 @@ class BIM_PT_gis(Panel):
             row.label(text=f"OrthogonalHeight ({GeoreferenceData.data['local_unit_symbol']})")
             row.label(text=props.blender_orthogonal_height)
             row = self.layout.row(align=True)
-            row.label(text="XAxisAbscissa")
-            row.label(text=props.blender_x_axis_abscissa)
-            row = self.layout.row(align=True)
-            row.label(text="XAxisOrdinate")
-            row.label(text=props.blender_x_axis_ordinate)
-            row = self.layout.row(align=True)
-            row.label(text="Derived Grid North")
-            row.label(text=GeoreferenceData.data["blender_derived_angle"])
+            row.label(text="Angle to Grid North")
+            row.label(text=props.blender_project_north)
 
         if GeoreferenceData.data["projected_crs"]:
             row = self.layout.row(align=True)
@@ -144,7 +138,7 @@ class BIM_PT_gis(Panel):
             row.label(text=str(value))
             if key == "XAxisOrdinate":
                 row = self.layout.row(align=True)
-                row.label(text="Derived Angle")
+                row.label(text="*Angle to Grid North")
                 row.label(text=GeoreferenceData.data["map_derived_angle"])
 
 
@@ -195,7 +189,7 @@ class BIM_PT_gis_true_north(Panel):
             row.operator("bim.enable_editing_true_north", icon="GREASEPENCIL", text="")
             row.operator("bim.remove_true_north", icon="X", text="")
             row = self.layout.row(align=True)
-            row.label(text="Derived Angle")
+            row.label(text="*Angle to True North")
             row.label(text=GeoreferenceData.data["true_derived_angle"])
         else:
             row = self.layout.row(align=True)

src/blenderbim/blenderbim/bim/module/project/operator.py

@@ -918,6 +918,8 @@ class LinkIfc(bpy.types.Operator):
         if pprops.false_origin_mode == "MANUAL":
             row = self.layout.row()
             row.prop(pprops, "false_origin")
+            row = self.layout.row()
+            row.prop(pprops, "project_north")
 
     def execute(self, context):
         start = time.time()
@@ -1071,6 +1073,7 @@ def run():
     pprops.distance_limit = {pprops.distance_limit}
     pprops.false_origin_mode = "{pprops.false_origin_mode}"
     pprops.false_origin = "{pprops.false_origin}"
+    pprops.project_north = "{pprops.project_north}"
     bpy.ops.bim.load_linked_project(filepath="{self.filepath}")
     bpy.ops.wm.save_as_mainfile(filepath="{blend_filepath}")
 
@@ -1413,6 +1416,7 @@ class LoadLinkedProject(bpy.types.Operator):
             "distance_limit": pprops.distance_limit,
             "false_origin_mode": pprops.false_origin_mode,
             "false_origin": pprops.false_origin,
+            "project_north": pprops.project_north,
         }
         with open(self.json_filepath, "w") as f:
             json.dump(data, f)

src/blenderbim/blenderbim/bim/module/project/prop.py

@@ -171,6 +171,11 @@ class BIMProjectProperties(PropertyGroup):
         description="False origin in project units that the Blender origin will correlate to",
         default="0,0,0",
     )
+    project_north: StringProperty(
+        name="Angle to Grid North",
+        description="The angle (postive is anticlockwise) pointing to grid north relative to project north",
+        default="0",
+    )
     element_offset: IntProperty(name="Element Offset", default=0)
     element_limit: IntProperty(name="Element Offset", default=30000)
     should_disable_undo_on_save: BoolProperty(

src/blenderbim/blenderbim/bim/module/project/ui.py

@@ -175,6 +175,8 @@ class BIM_PT_project(Panel):
         if pprops.false_origin_mode == "MANUAL":
             row = self.layout.row()
             row.prop(pprops, "false_origin")
+            row = self.layout.row()
+            row.prop(pprops, "project_north")
 
         row = self.layout.row()
         row.label(text="Element Range")

src/blenderbim/blenderbim/tool/georeference.py

@@ -91,7 +91,7 @@ class Georeference(blenderbim.core.tool.Georeference):
             elif name == "XAxisAbscissa":
                 props = bpy.context.scene.BIMGeoreferenceProperties
                 props.is_changing_angle = True
-                if data["XAxisAbscissa"] is None or data["XAxisOrdinate"]:
+                if data["XAxisAbscissa"] is None or data["XAxisOrdinate"] is None:
                     props.x_axis_is_null = True
                 else:
                     props.grid_north_angle = str(

src/blenderbim/blenderbim/tool/loader.py

@@ -568,15 +568,36 @@ class Loader(blenderbim.core.tool.Loader):
         false_origin = np.array(cls.settings.false_origin)
         model_offset = false_origin - model_origin
         zero_origin = np.array((0, 0, 0))
-        has_model_offset = not np.allclose(model_offset, zero_origin)
-        if has_model_offset:
+        has_offset = not np.allclose(model_offset, zero_origin)
+
+        parameters = ifcopenshell.util.geolocation.get_helmert_transformation_parameters(ifc_file)
+        model_north = ifcopenshell.util.geolocation.xaxis2angle(parameters.xaa, parameters.xao)
+        project_north = cls.settings.project_north
+        model_rotation = project_north - model_north
+        if model_rotation > 180:
+            model_rotation = (360 - model_rotation) * -1
+        elif model_rotation < -180:
+            model_rotation = (model_rotation * -1) - 360
+        has_rotation = not np.isclose(model_north, project_north)
+
+        if not has_offset:
+            model_offset = false_origin = (0, 0, 0)
+
+        if not has_rotation:
+            project_north = 0
+
+        if has_offset or has_rotation:
             props = bpy.context.scene.BIMGeoreferenceProperties
-            props.blender_offset_x = str(model_offset[0])
-            props.blender_offset_y = str(model_offset[1])
-            props.blender_offset_z = str(model_offset[2])
             props.blender_eastings = str(false_origin[0])
             props.blender_northings = str(false_origin[1])
             props.blender_orthogonal_height = str(false_origin[2])
+            props.blender_project_north = str(project_north)
+            props.blender_offset_x = str(model_offset[0])
+            props.blender_offset_y = str(model_offset[1])
+            props.blender_offset_z = str(model_offset[2])
+            xaa, xao = ifcopenshell.util.geolocation.angle2xaxis(model_rotation)
+            props.blender_x_axis_abscissa = str(xaa)
+            props.blender_x_axis_ordinate = str(xao)
             props.has_blender_offset = True
 
     @classmethod

src/ifcopenshell-python/ifcopenshell/util/geolocation.py

@@ -543,7 +543,9 @@ def xaxis2angle(x: float, y: float) -> float:
     the page?". See the diagram on the IfcGeometricRepresentationContext
     documentation for clarification.
 
-    The angle indicates "how do I rotate grid east to get to project east?".
+    The angle indicates "how do I rotate project east to get to grid east?".
+    Alternatively: "how do I rotate project north to get to grid north?".
+    Positive angles are anticlockwise.
 
     :param x: The X axis abscissa
     :param y: The X axis ordinate
@@ -562,6 +564,7 @@ def yaxis2angle(x: float, y: float) -> float:
     documentation for clarification.
 
     The angle indicates "how do I rotate project north to get to true north?".
+    Positive angles are anticlockwise.
 
     :param x: The Y axis abscissa
     :param y: The Y axis ordinate