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.

[adam-urbanczyk]

I tried with SetCasCadeLengthUnit, but still getting the length issue. I will come up with a proper MRE, but I'm starting to think that there is a bug in 7.8 or at least an unexpected change of semantics.

[dpasukhi]

Calling of that parameter must be done before creating of the writer object AND after initing of controller. If later - only changing directly from model interface.
It can be a bug, I'm not sure now. In 8.0 there will be no interface_static parameters

[dpasukhi]

Well, in version 7.9 I found an issue with inconsistent of the write schema - I will fix it.
But as for a 7.8, direct implementation of the units to model will help in any case.

[dpasukhi]

Well, thank you. It is a bug even for 7.9 (related to ignore the write.step.unit in any cases.
Only applying the scale to the model after creating will be help. My apologies, our tests rely on applying on model that.

[whophil]

Thank you for looking into this @dpasukhi . I just want to confirm with you - both 7.8 and 7.9 have the issue where write.step.unit is ignored?

[dpasukhi]

From initialization yes, 7.9 will be fixed before release.
But you are able to apply it (7.8 and 7.9_Beta1). The solution:

   STEPControl_Writer aWriter; 
   Handle(StepData_StepModel) aModel     = aWriter.Model(); 
   aModel->SetLocalLengthUnit(1); 
   aModel->SetWriteLengthUnit(1000); 

[dpasukhi]

Issue: #354
Will be fixed during a week. My apologies. If you will have any other bugs - please create an issue reports.

[whophil]

Thanks @dpasukhi ! I can confirm that the SetWriteLengthUnit(1000) works to scale the values in the STP file with OCCT 7.8.

However, it does not affect the LENGTH_UNIT() directive in STP files. In OCCT 7.7 and earlier, write.step.unit does modify this line. I just wanted to point this out in case it was missed in the current tests. Thanks very much.

#346 = ( LENGTH_UNIT() NAMED_UNIT(*) SI_UNIT(.MILLI.,.METRE.) );