Offset a Wire or a Shape?

If you are simply looking to offset a wire or shape along a spine, check out the BRepOffsetAPI package. There are several classes to choose from, depending on the type of offset you need.

Hi Rob,

Thanks for the tips.

I tried the BRepOffsetAPI_MakeOffset function as following

TopoDS_Face myFace = TopoDS::Face(faceTmp->Value(1));
BRepOffsetAPI_MakeOffset myOffSet.Init(myFace,GeomAbs_Arc);

crashed here---> myOffSet.Perform(1.5,1.5);

I looked the the documents, I think it is correct.

by any chance, do you know what was missing?

Thanks in advance

Try leaving out the Init. You only call Init if you use the default constructor or you are reusing the same algorithm with different parameters.

TopoDS_Face myFace = TopoDS::Face(faceTmp->Value(1));
BRepOffsetAPI_MakeOffset myOffSet(myFace,GeomAbs_Arc);

crashed here---> myOffSet.Perform(1.5,1.5);

Hi Rob,

Even without init it, it is still crashed on Perform.
and after perform, how could I make it a topods shape to display in the 3d view?

Thanks in Advance

In general, your code looks OK. It is possible that there is something wrong with the face being fed to it (must be planar). It also appears that MakeOffset is a little sensitive. If you look at the documentation for the mkoffset command (which calls BRepOffsetAPI_MakeOffset) in the Test Harness User's Guide (section 7.2.6), there is a note:

"The mkoffset command must be used with prudence, angular contours produce offset contours and fillets. Interior parallel contours can produce more than one wire, normally these are refused. ..."

I tried the test harness with a square face and it works fine, but I could see some faces having problems.

For display purposes, you can get the resulting TopoDS_Shape objects with the Shape function (from the BRepBuilderAPI_MakeShape base class).

I also suggest you try catching exceptions. Maybe an exception is being thrown that can give you additional information on the problem.

Good luck,
Commenter-1

Hi Rob,

You are correct, Thanks for the advise and the tips.

Rice