Added quality controls to STEP export for shape and assembly

Author: jmwright

cadquery/assembly.py

@@ -420,6 +420,7 @@ def save(
         exportType: Optional[ExportLiterals] = None,
         tolerance: float = 0.1,
         angularTolerance: float = 0.1,
+        **kwargs,
     ) -> "Assembly":
         """
         save as STEP or OCCT native XML file
@@ -438,7 +439,7 @@ def save(
                 raise ValueError("Unknown extension, specify export type explicitly")
 
         if exportType == "STEP":
-            exportAssembly(self, path)
+            exportAssembly(self, path, **kwargs)
         elif exportType == "XML":
             exportCAF(self, path)
         elif exportType == "VRML":

cadquery/occ_impl/exporters/assembly.py

@@ -21,22 +21,48 @@
 from OCP.RWGltf import RWGltf_CafWriter
 from OCP.TColStd import TColStd_IndexedDataMapOfStringString
 from OCP.Message import Message_ProgressRange
+from OCP.Interface import Interface_Static
 
 from ..assembly import AssemblyProtocol, toCAF, toVTK
 
 
-def exportAssembly(assy: AssemblyProtocol, path: str) -> bool:
+def exportAssembly(assy: AssemblyProtocol, path: str, **kwargs) -> bool:
     """
     Export an assembly to a step a file.
+
+    kwargs is used to provide optional keyword arguments to configure the exporter.
+    The current parameters are as follows:
+
+    :param write_pcurves: Enables or disables P-Curve entities written to STEP file
+    :type write_pcurves: boolean
+    :param precision_mode: Sets the precision mode of the OCCT STEP exporter
+    :type precision_mode: int
+
+    The default behaviour of the OCCT STEP file writer is to add redundant
+    P-Curve entities to the STEP file.  This can often double the size of the
+    resulting STEP file.  Turning off P-Curves can save file size and almost
+    never impacts the quality of the STEP file.
+
+    The precision mode parameter coresponds to the OCCT STEP file precision
+    for writing geometric data.  The default value of 1 for maximum precision
+    is used by can be changed if desired.
     """
 
+    # Handle the extra settings for the STEP export
+    pcurves = 1
+    if "write_pcurves" in kwargs and not kwargs["write_pcurves"]:
+        pcurves = 0
+    precision_mode = kwargs["precision_mode"] if "precision_mode" in kwargs else 1
+
     _, doc = toCAF(assy, True)
 
     session = XSControl_WorkSession()
     writer = STEPCAFControl_Writer(session, False)
     writer.SetColorMode(True)
     writer.SetLayerMode(True)
     writer.SetNameMode(True)
+    Interface_Static.SetIVal_s("write.surfacecurve.mode", pcurves)
+    Interface_Static.SetIVal_s("write.precision.mode", precision_mode)
     writer.Transfer(doc, STEPControl_StepModelType.STEPControl_AsIs)
 
     status = writer.Write(path)

cadquery/occ_impl/shapes.py

@@ -230,6 +230,8 @@
 # for catching exceptions
 from OCP.Standard import Standard_NoSuchObject, Standard_Failure
 
+from OCP.Interface import Interface_Static
+
 from math import pi, sqrt
 import warnings
 
@@ -449,12 +451,37 @@ def exportStl(
 
         return writer.Write(self.wrapped, fileName)
 
-    def exportStep(self, fileName: str) -> IFSelect_ReturnStatus:
+    def exportStep(self, fileName: str, **kwargs) -> IFSelect_ReturnStatus:
         """
         Export this shape to a STEP file
+
+        kwargs is used to provide optional keyword arguments to configure the exporter.
+        The current parameters are as follows:
+
+        :param write_pcurves: Enables or disables P-Curve entities written to STEP file
+        :type write_pcurves: boolean
+        :param precision_mode: Sets the precision mode of the OCCT STEP exporter
+        :type precision_mode: int
+
+        The default behaviour of the OCCT STEP file writer is to add redundant
+        P-Curve entities to the STEP file.  This can often double the size of the
+        resulting STEP file.  Turning off P-Curves can save file size and almost
+        never impacts the quality of the STEP file.
+
+        The precision mode parameter coresponds to the OCCT STEP file precision
+        for writing geometric data.  The default value of 1 for maximum precision
+        is used by can be changed if desired.
         """
 
+        # Handle the extra settings for the STEP export
+        pcurves = 1
+        if "write_pcurves" in kwargs and not kwargs["write_pcurves"]:
+            pcurves = 0
+        precision_mode = kwargs["precision_mode"] if "precision_mode" in kwargs else 1
+
         writer = STEPControl_Writer()
+        Interface_Static.SetIVal_s("write.surfacecurve.mode", pcurves)
+        Interface_Static.SetIVal_s("write.precision.mode", precision_mode)
         writer.Transfer(self.wrapped, STEPControl_AsIs)
 
         return writer.Write(fileName)