Archived issue #0029060
BRepOffset_MakeOffset produces invalid shape in test bugs modalg_7 bug28131
Description
Standard offset algorithm BRepOffset_MakeOffset produces invalid shape in test bugs modalg_7 bug28131 (see #0028131). The current version of the test calls fixshape to fix the result shape, and this leads to increasing of the tolerance.
It is needed to investigate why the result is invalid.
It is needed to investigate why the result is invalid.
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Investigation revealed that the input b-spline surface has such properties near the degeneracy that its offset has "corrupted" degeneracy. Please see the attached snapshot Attachment 1 (PNG). The degeneracy point is shifted from the corner of the surface along one of boundary to the inside. At this, the place between the corner and degeneracy behaves like a "black hole" - there is difficult to find a parameters (u,v) to hit into this area.
The offset algorithm creates an edge to cover this part of boundary, and this edge is not degenerated. However, the correspondence of 3D curve and p-curve cannot be fulfilled, and the edge is reported to have invalid curve on surface.
In the scope of this issue it is needed to modify the offset algorithm so that to provide setting to the edge the enough tolerance to cover the same-parameter error.
The offset algorithm creates an edge to cover this part of boundary, and this edge is not degenerated. However, the correspondence of 3D curve and p-curve cannot be fulfilled, and the edge is reported to have invalid curve on surface.
In the scope of this issue it is needed to modify the offset algorithm so that to provide setting to the edge the enough tolerance to cover the same-parameter error.
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