Did something changed regarding units from 7.7 to 7.8

[adam-urbanczyk]

The following code used to work with 7.7

from OCP import Interface, STEPControl, gp, BRepBuilderAPI

# make a point
pnt = gp.gp_Pnt(1, 0, 0)
vertex = BRepBuilderAPI.BRepBuilderAPI_MakeVertex(pnt).Vertex()

# instantiate writer
w = STEPControl.STEPControl_Writer()

# set units
model_units = 'MM'
output_units = 'M'

if not Interface.Interface_Static.SetCVal_s('xstep.cascade.unit', model_units):
    raise ValueError

if not Interface.Interface_Static.SetCVal_s('write.step.unit', output_units):
    raise ValueError

# transfer shapes and write
w.Transfer(vertex, STEPControl.STEPControl_AsIs)
w.Write("test.stp")

With 7.8 it results in a step containing

#16 = CARTESIAN_POINT('',(1.,0.,0.));

Is this a regression/bug? I did not see anything obvious in the release notes.

See https://dev.opencascade.org/content/differences-behavior-units-xstepcascadeunit-and-stepcontrolwriter-75-76 for reference.

[adam-urbanczyk]

I also tried OCP.UnitsMethods.UnitsMethods.SetCasCadeLengthUnit_s() but it seems to also not have any effect.

[dpasukhi]

Hello @adam-urbanczyk, yes, changed the way of extraction. Putting unit into CValue is not a complete solution.
And more changes on 7.9 (about single input parameters for DE Shape healing and any other parameters in single structure).

Please check the way to getting up units:

OCCT/src/XSDRAW/XSDRAW.cxx

Lines 366 to 381 in cc30b93

	Standard_Real XSDRAW::GetLengthUnit(const Handle(TDocStd_Document)& theDoc)
	{
	if (!theDoc.IsNull())
	{
	Standard_Real aUnit = 1.;
	if (XCAFDoc_DocumentTool::GetLengthUnit(theDoc, aUnit, UnitsMethods_LengthUnit_Millimeter))
	{
	return aUnit;
	}
	}
	if (Interface_Static::IsPresent("xstep.cascade.unit"))
	{
	UnitsMethods::SetCasCadeLengthUnit(Interface_Static::IVal("xstep.cascade.unit"));
	}
	return UnitsMethods::GetCasCadeLengthUnit();
	}

To update units needs to work with UnitsMethods. Or use STEPControl_Writer::Transfer that take a parameter or you can use that sample:

OCCT/src/DESTEP/DESTEP_Provider.cxx

Lines 233 to 283 in cc30b93

	{
	if (GetNode().IsNull() || !GetNode()->IsKind(STANDARD_TYPE(DESTEP_ConfigurationNode)))
	{
	Message::SendFail() << "Error in the DESTEP_Provider during reading the file " << thePath
	<< "\t: Incorrect or empty Configuration Node";
	return false;
	}
	Handle(DESTEP_ConfigurationNode) aNode = Handle(DESTEP_ConfigurationNode)::DownCast(GetNode());
	personizeWS(theWS);
	STEPControl_Writer aWriter;
	aWriter.SetWS(theWS);
	IFSelect_ReturnStatus aWritestat = IFSelect_RetVoid;
	Handle(StepData_StepModel) aModel = aWriter.Model();
	;
	DESTEP_Parameters aParams = aNode->InternalParameters;
	aModel->SetLocalLengthUnit(aNode->GlobalParameters.SystemUnit);
	UnitsMethods_LengthUnit aTargetUnit =
	UnitsMethods::GetLengthUnitByFactorValue(aNode->GlobalParameters.LengthUnit,
	UnitsMethods_LengthUnit_Millimeter);
	aParams.WriteUnit = aTargetUnit;
	if (aTargetUnit == UnitsMethods_LengthUnit_Undefined)
	{
	aModel->SetWriteLengthUnit(1.0);
	Message::SendWarning()
	<< "Custom units are not supported by STEP format, but LengthUnit global parameter doesn't "
	"fit any predefined unit. Units will be scaled to Millimeters";
	}
	else
	{
	aModel->SetWriteLengthUnit(aNode->GlobalParameters.LengthUnit);
	}
	aWriter.SetShapeFixParameters(aNode->ShapeFixParameters);
	aWritestat = aWriter.Transfer(theShape,
	aNode->InternalParameters.WriteModelType,
	aParams,
	true,
	theProgress);
	if (aWritestat != IFSelect_RetDone)
	{
	Message::SendFail() << "Error in the DESTEP_Provider during reading the file " << thePath
	<< "\t: abandon, no model loaded";
	return false;
	}
	if (aWriter.Write(thePath.ToCString()) != IFSelect_RetDone)
	{
	Message::SendFail() << "DESTEP_Provider: Error on writing file";
	return false;
	}
	return true;
	}

Additionally, I would recommend to init static variables before writer creating (STEPControl_Controller::Init() then setting up static values)

And it is for the no XCAF implementation there are more possible inputs (like document of the document).
I will try to prepare more detailed logs for 7.9