Added unit handling to STEP import and export

.gitignore

@@ -1,4 +1,5 @@
 build/
+__pycache__
 *.pyc
 doc/_build/*
 dist/*

cadquery/__init__.py

@@ -21,6 +21,7 @@
 )
 from .occ_impl import exporters
 from .occ_impl import importers
+from .occ_impl.types import STEPUnitLiterals
 
 # these items are the common implementation
 
@@ -75,6 +76,6 @@
     "DirectionMinMaxSelector",
     "StringSyntaxSelector",
     "Selector",
-    "plugins",
     "Sketch",
+    "STEPUnitLiterals",
 ]

cadquery/assembly.py

@@ -37,6 +37,8 @@
 )
 from .occ_impl.importers.assembly import importStep as _importStep, importXbf, importXml
 
+from .occ_impl.types import STEPUnitLiterals
+
 from .selectors import _expression_grammar as _selector_grammar
 from .utils import deprecate, BiDict, instance_of
 
@@ -618,18 +620,24 @@ def export(
         return self
 
     @classmethod
-    def importStep(cls, path: str) -> Self:
+    def importStep(cls, path: str, unit: STEPUnitLiterals = "MM") -> Self:
         """
         Reads an assembly from a STEP file.
 
         :param path: Path and filename for reading.
+        :param unit: The unit of measurement for the STEP file. Default "MM".
         :return: An Assembly object.
         """
 
-        return cls.load(path, importType="STEP")
+        return cls.load(path, importType="STEP", unit=unit)
 
     @classmethod
-    def load(cls, path: str, importType: Optional[ImportLiterals] = None,) -> Self:
+    def load(
+        cls,
+        path: str,
+        importType: Optional[ImportLiterals] = None,
+        unit: STEPUnitLiterals = "MM",
+    ) -> Self:
         """
         Load step, xbf or xml.
         """
@@ -644,7 +652,7 @@ def load(cls, path: str, importType: Optional[ImportLiterals] = None,) -> Self:
         assy = cls()
 
         if importType == "STEP":
-            _importStep(assy, path)
+            _importStep(assy, path, unit)
         elif importType == "XML":
             importXml(assy, path)
         elif importType == "XBF":

cadquery/occ_impl/exporters/assembly.py

@@ -48,6 +48,7 @@
 from ..assembly import AssemblyProtocol, toCAF, toVTK, toFusedCAF
 from ..geom import Location
 from ..shapes import Shape, Compound
+from ..types import STEPUnitLiterals
 
 
 class ExportModes:
@@ -62,6 +63,8 @@ def exportAssembly(
     assy: AssemblyProtocol,
     path: str,
     mode: STEPExportModeLiterals = "default",
+    unit: STEPUnitLiterals = "MM",
+    outputUnit: Optional[STEPUnitLiterals] = None,
     **kwargs,
 ) -> bool:
     """
@@ -73,6 +76,12 @@ def exportAssembly(
     :param path: Path and filename for writing
     :param mode: STEP export mode. The options are "default", and "fused" (a single fused compound).
         It is possible that fused mode may exhibit low performance.
+    :param unit: The internal unit of the model's geometry values. Default "MM".
+    :type unit: STEPUnitLiterals
+    :param outputUnit: The unit to use in the STEP file header. If None, defaults to the value of ``unit``.
+        Use this when you want the output file to declare a different unit than the model's internal unit,
+        for example to export a MM model as a STEP file declaring meters.
+    :type outputUnit: STEPUnitLiterals or None
     :param fuzzy_tol: OCCT fuse operation tolerance setting used only for fused assembly export.
     :type fuzzy_tol: float
     :param glue: Enable gluing mode for improved performance during fused assembly export.
@@ -113,6 +122,10 @@ def exportAssembly(
     Interface_Static.SetIVal_s("write.surfacecurve.mode", pcurves)
     Interface_Static.SetIVal_s("write.precision.mode", precision_mode)
     Interface_Static.SetIVal_s("write.stepcaf.subshapes.name", 1)
+    Interface_Static.SetCVal_s("xstep.cascade.unit", unit)
+    Interface_Static.SetCVal_s(
+        "write.step.unit", outputUnit if outputUnit is not None else unit
+    )
     writer.Transfer(doc, STEPControl_StepModelType.STEPControl_AsIs)
 
     if name_geometries:
@@ -157,6 +170,8 @@ def exportStepMeta(
     path: str,
     write_pcurves: bool = True,
     precision_mode: int = 0,
+    unit: STEPUnitLiterals = "MM",
+    outputUnit: Optional[STEPUnitLiterals] = None,
 ) -> bool:
     """
     Export an assembly to a STEP file with faces tagged with names and colors. This is done as a
@@ -172,6 +187,12 @@ def exportStepMeta(
         If False, writes STEP file without pcurves. This decreases the size of the resulting STEP file.
     :param precision_mode: Controls the uncertainty value for STEP entities. Specify -1, 0, or 1. Default 0.
         See OCCT documentation.
+    :param unit: The internal unit of the model's geometry values. Default "MM".
+    :type unit: STEPUnitLiterals
+    :param outputUnit: The unit to use in the STEP file header. If None, defaults to the value of ``unit``.
+        Use this when you want the output file to declare a different unit than the model's internal unit,
+        for example to export a MM model as a STEP file declaring meters.
+    :type outputUnit: STEPUnitLiterals or None
     """
 
     pcurves = 1
@@ -311,6 +332,10 @@ def _process_assembly(
     writer.SetNameMode(True)
     Interface_Static.SetIVal_s("write.surfacecurve.mode", pcurves)
     Interface_Static.SetIVal_s("write.precision.mode", precision_mode)
+    Interface_Static.SetCVal_s("xstep.cascade.unit", unit)
+    Interface_Static.SetCVal_s(
+        "write.step.unit", outputUnit if outputUnit is not None else unit
+    )
     writer.Transfer(doc, STEPControl_StepModelType.STEPControl_AsIs)
 
     status = writer.Write(path)

cadquery/occ_impl/importers/__init__.py

@@ -3,10 +3,12 @@
 
 import OCP.IFSelect
 from OCP.STEPControl import STEPControl_Reader
+from OCP.Interface import Interface_Static
 
 from ... import cq
 from ..shapes import Shape
 from .dxf import _importDXF
+from ..types import STEPUnitLiterals
 
 RAD2DEG = 360.0 / (2 * pi)
 
@@ -24,18 +26,24 @@ class UNITS:
 
 
 def importShape(
-    importType: Literal["STEP", "DXF", "BREP", "BIN"], fileName: str, *args, **kwargs
+    importType: Literal["STEP", "DXF", "BREP", "BIN"],
+    fileName: str,
+    unit: STEPUnitLiterals = "MM",
+    *args,
+    **kwargs,
 ) -> "cq.Workplane":
     """
     Imports a file based on the type (STEP, STL, etc)
 
     :param importType: The type of file that we're importing
     :param fileName: The name of the file that we're importing
+    :param unit: The unit of measurement for the STEP file. Default "MM".
+    :type unit: STEPUnitLiterals
     """
 
     # Check to see what type of file we're working with
     if importType == ImportTypes.STEP:
-        return importStep(fileName)
+        return importStep(fileName, unit)
     elif importType == ImportTypes.DXF:
         return importDXF(fileName, *args, **kwargs)
     elif importType == ImportTypes.BREP:
@@ -76,13 +84,20 @@ def importBin(fileName: str) -> "cq.Workplane":
 
 
 # Loads a STEP file into a CQ.Workplane object
-def importStep(fileName: str) -> "cq.Workplane":
+def importStep(fileName: str, unit: STEPUnitLiterals = "MM") -> "cq.Workplane":
     """
     Accepts a file name and loads the STEP file into a cadquery Workplane
 
     :param fileName: The path and name of the STEP file to be imported
+    :param unit: The assumed unit of measurement when the STEP file does not
+      declare one in its header. Has no effect when the file already contains
+      a unit declaration. Default "MM".
+    :type unit: STEPUnitLiterals
     """
 
+    # Set the assumed length unit for STEP import in case it is missing from the STEP header
+    Interface_Static.SetCVal_s("read.step.unit", unit)
+
     # Now read and return the shape
     reader = STEPControl_Reader()
     readStatus = reader.ReadFile(fileName)

cadquery/occ_impl/importers/assembly.py

@@ -26,6 +26,7 @@
 from ..assembly import AssemblyProtocol, Color, Material
 from ..geom import Location
 from ..shapes import Shape
+from ..types import STEPUnitLiterals
 
 
 def _get_name(label: TDF_Label) -> str:
@@ -129,12 +130,15 @@ def _get_shape_color(s: TopoDS_Shape, color_tool: XCAFDoc_ColorTool) -> Color |
     return rv
 
 
-def importStep(assy: AssemblyProtocol, path: str):
+def importStep(assy: AssemblyProtocol, path: str, unit: STEPUnitLiterals = "MM"):
     """
     Import a step file into an assembly.
 
     :param assy: An Assembly object that will be packed with the contents of the STEP file.
     :param path: Path and filename to the STEP file to read.
+    :param unit: The assumed unit of measurement when the STEP file does not
+      declare one in its header. Has no effect when the file already contains
+      a unit declaration. Default "MM".
 
     :return: None
     """
@@ -147,6 +151,7 @@ def importStep(assy: AssemblyProtocol, path: str):
     step_reader.SetSHUOMode(True)
 
     Interface_Static.SetIVal_s("read.stepcaf.subshapes.name", 1)
+    Interface_Static.SetCVal_s("read.step.unit", unit)
 
     # Read the STEP file
     status = step_reader.ReadFile(path)

cadquery/occ_impl/shapes.py

@@ -34,6 +34,7 @@
 )
 
 from ..utils import multimethod, multidispatch, mypyclassmethod
+from .types import STEPUnitLiterals
 
 # change default OCCT logging level
 from OCP.Message import Message, Message_Gravity
@@ -511,15 +512,26 @@ def exportStl(
 
         return writer.Write(self.wrapped, fileName)
 
-    def exportStep(self, fileName: str, **kwargs) -> IFSelect_ReturnStatus:
+    def exportStep(
+        self,
+        fileName: str,
+        unit: STEPUnitLiterals = "MM",
+        outputUnit: Optional[STEPUnitLiterals] = None,
+        **kwargs,
+    ) -> IFSelect_ReturnStatus:
         """
         Export this shape to a STEP file.
-
-        kwargs is used to provide optional keyword arguments to configure the exporter.
+        kwargs is used to provide additional optional keyword arguments to configure the exporter.
 
         :param fileName: Path and filename for writing.
+        :type fileName: str
+        :param unit: The internal unit of the model's geometry values. Default "MM".
+        :type unit: STEPUnitLiterals
+        :param outputUnit: The unit to use in the STEP file header. If None, defaults to the value of ``unit``.
+            Use this when you want the output file to declare a different unit than the model's internal unit,
+            for example to export a MM model as a STEP file declaring meters.
+        :type outputUnit: STEPUnitLiterals or None
         :param write_pcurves: Enable or disable writing parametric curves to the STEP file. Default True.
-
             If False, writes STEP file without pcurves. This decreases the size of the resulting STEP file.
         :type write_pcurves: bool
         :param precision_mode: Controls the uncertainty value for STEP entities. Specify -1, 0, or 1. Default 0.
@@ -536,6 +548,10 @@ def exportStep(self, fileName: str, **kwargs) -> IFSelect_ReturnStatus:
         writer = STEPControl_Writer()
         Interface_Static.SetIVal_s("write.surfacecurve.mode", pcurves)
         Interface_Static.SetIVal_s("write.precision.mode", precision_mode)
+        Interface_Static.SetCVal_s("xstep.cascade.unit", unit.upper())
+        Interface_Static.SetCVal_s(
+            "write.step.unit", outputUnit if outputUnit is not None else unit.upper()
+        )
         writer.Transfer(self.wrapped, STEPControl_AsIs)
 
         return writer.Write(fileName)
@@ -617,7 +633,7 @@ def geomType(self) -> Geoms:
         if isinstance(tr, str):
             rv = tr
         elif tr is BRepAdaptor_Curve:
-            rv = geom_LUT_EDGE[tr(self.wrapped).GetType()]
+            rv = geom_LUT_EDGE[tr(tcast(TopoDS_Edge, self.wrapped)).GetType()]
         else:
             rv = geom_LUT_FACE[tr(self.wrapped).GetType()]
 

cadquery/occ_impl/types.py

@@ -0,0 +1,3 @@
+from typing_extensions import Literal
+
+STEPUnitLiterals = Literal["MM", "CM", "M", "KM", "INCH", "FT", "MI", "UM", "NM"]

doc/importexport.rst

@@ -77,14 +77,22 @@ Importing STEP
 ###############
 
 STEP files can be imported using the :meth:`importers.importStep` method (note the capitalization of "Step").
-There are no parameters for this method other than the file path to import.
 
 .. code-block:: python
 
    import cadquery as cq
 
    result = cq.importers.importStep("/path/to/step/block.stp")
 
+By default, the unit declared in the STEP file's header is used, i.e. no conversion factor is applied when importing. If needed, the ``unit`` parameter can be used to specify to which unit it is converted. The valid values are defined by :class:`STEPUnitLiterals`: ``"MM"``, ``"CM"``, ``"M"``, ``"KM"``, ``"INCH"``, ``"FT"``, ``"MI"``, ``"UM"``, and ``"NM"``.
+
+.. code-block:: python
+
+   import cadquery as cq
+
+   # Import a STEP file that lacks a unit declaration, treating its values as meters
+   result = cq.importers.importStep("/path/to/step/block.stp", unit="M")
+
 Exporting STEP
 ###############
 
@@ -139,6 +147,35 @@ or the :meth:`Assembly.exportAssembly`` method.
    # or equivalently when exporting a lower level Shape object
    box.val().export("/path/to/step/box2.step", opt={"write_pcurves": False})
 
+Setting Units
+--------------
+
+By default, CadQuery exports STEP files with millimeter units.
+The ``unit`` parameter specifies the internal unit of the model's geometry values.
+The ``outputUnit`` parameter controls the unit written to the STEP file header.
+If ``outputUnit`` is not specified, it defaults to the value of ``unit``.
+The valid values for both parameters are defined by :class:`STEPUnitLiterals`: ``"MM"``, ``"CM"``, ``"M"``, ``"KM"``, ``"INCH"``, ``"FT"``, ``"MI"``, ``"UM"``, and ``"NM"``.
+
+To export a millimeter model as a STEP file declaring meters, set ``outputUnit="M"`` while leaving ``unit`` at its default of ``"MM"``.
+OCCT will scale the coordinate values accordingly.
+
+.. code-block:: python
+
+   import cadquery as cq
+
+   # Create a simple object
+   box = cq.Workplane().box(10, 10, 10)
+
+   # Export with meter units
+   box.val().exportStep("/path/to/step/box.step", outputUnit="M")
+
+For assemblies, see the ``outputUnit`` parameter example in the exporting assemblies section.
+
+.. note::
+
+   CadQuery treats all geometry values as millimeters internally.
+   If you built a model using values that represent meters (e.g. a box with side length ``10`` meaning 10 meters), you must scale the geometry by 1000 before exporting, then export with the default ``unit="MM"``.
+   Exporting such a model directly with ``outputUnit="M"`` will produce a STEP file representing a 0.01-meter (10mm) object, not a 10-meter one.
 
 Exporting Assemblies
 ####################
@@ -176,6 +213,36 @@ export with all defaults is shown below.
 This will produce a STEP file that is nested with auto-generated object names. The colors of each assembly object will be
 preserved, but the names that were set for each will not.
 
+Setting Units
+--------------
+
+By default, CadQuery exports STEP files with millimeter units.
+The ``unit`` parameter specifies the internal unit of the model's geometry values.
+The ``outputUnit`` parameter controls the unit written to the STEP file header.
+If ``outputUnit`` is not specified, it defaults to the value of ``unit``.
+The valid values for both parameters are defined by :class:`STEPUnitLiterals`: ``"MM"``, ``"CM"``, ``"M"``, ``"KM"``, ``"INCH"``, ``"FT"``, ``"MI"``, ``"UM"``, and ``"NM"``.
+The default is ``"MM"``.
+
+To export a millimeter model as a STEP file declaring meters, set ``outputUnit="M"`` while leaving ``unit`` at its default of ``"MM"``.
+OCCT will scale the coordinate values accordingly.
+
+.. code-block:: python
+
+   import cadquery as cq
+
+   assy = cq.Assembly()
+   assy.add(cq.Workplane().box(10, 10, 10), name="box")
+
+   # Export the assembly with meter units
+   assy.export("/path/to/step/assy.step", outputUnit="M")
+
+.. note::
+
+   CadQuery treats all geometry values as millimeters internally.
+   If you built a model using values that represent meters (e.g. a box with side length ``10`` meaning 10 meters), you must scale the geometry by 1000 before exporting, then export with the default ``unit="MM"``.
+   Exporting such a model directly with ``outputUnit="M"`` will produce a STEP file representing a 0.01-meter
+   (10mm) object, not a 10-meter one.
+
 Fused
 ------