Wed, 10/11/2017 - 20:46
Forums:
Hi , I am trying to trim a NURB and the result is unexpected ( OCC 7.2.0)
- I have an untrimmed NURB ( untrimmed_surface.brep)
- I have projected a polygonal boundary onto the NURB to create a UV polygon ( these UV locations evaluated on the NURB are trimmingWire3DOnSurface.brep).
- untrimmed_surface_with_uv_trimming_wire.png shows the trimming polygon evaluated on the NURB surface.
- As a 'trimming curve' needs to be an actual curve I create a periodic spline of degree 1 using Geom2dAPI_PointsToBSpline that interpolates the polygonal UV locations and apply that as a trimming curve on the NURB surface
- In 2D UV space the trimming curve is trimmingUVCurve2d.brep
- It interpolates and overlays the piece wise UV polygon trimmingWireUV.brep
- To me this implies I have created a correct UV trimming curve
- However, the result is unexpected when the trimming curve is applied to the NURB surface - see untrimmedsurface_with_trimming_spline.png
- The trimming curve does not follow the expected outline, it has developed some 'lobes' at the corners.
- The final "trimmed" NURB is trimmed_surface.brep
Attachments:
Mon, 10/23/2017 - 21:44
After much digging around, and some great help from OpenCASCADE experts, the fundamental issue is that the NURB surface is of degree 14. Trying to come up with a trimming curve that behaves as one might intuitively expect is very difficult in some areas of the surface.