Wireframe vs Shaded geometry difference for STEP file import.

Hello All,

I have a STEP file attached below - 'Prototype_IS.STP' which has a plate with some through holes on that plate. When i open that file in CAD Assistant and set Display mode to Shaded, It shows all curves and Geometry correctly - As in attached 'Shaded.PNG'. But when i set display mode to Wireframe some curves or geometry is shown incorrectly or extra curves or unbound curves are seen - As in attached 'Wireframe.PNG'. How can i fix this or get information about that wrong curve so that i should get only the correct curves information on STEP import for wireframe mode also. Please help me with this issue.

When i open the same file in NX, SolidWorks or any other CAD, they can show the file properly in both shaded and wireframe mode.

Thanks in advance.

PG's picture

have u opened in OCC based test harness ?

vishwas.mane_144577's picture

No. I have opened the file in CAD Assistance - OCC based viewer. Also i have tried to import the file with  STEPControl_Reader API, Withi this also the data i am getting is extra curves.

Kirill Gavrilov's picture

These are not "normal" curves in Wireframe mode, but surface Isolines appearing at visualization level (e.g. it is not a model bug).
The issue occurs on very tiny faces on your model - due to a known issue in OCCT isoline builder relying on some discretization to cut natural (unbound) surface isolines by Face boundaries, so that in some cases isolines are not properly cut.

The simplest workaround is enabling option "Map isolines onto triangulation" in CAD Assistant Settings (Visualization Options).

Fill free contacting Open CASCADE if you are interested in fixing an original issue (without workaround):

vishwas.mane_144577's picture

Hello Kirill,

Thank you for reply. Means if i want to get proper curve on OCC step import, the only way is OCC should fix it right? Or Can we identify that for a specific curve it's failed, means isoline builder was not succeeded or the curve has some wrong data. Or can i fix it manually at my end if i get such curve. Actually i am working on the data after STEP file import. Do we have any option for STEPControl_Reader or any other fix.

Thanks again.

Kirill Gavrilov's picture

First, the STEP file is imported by OCCT correctly - checkshape does not indicated any failures, so that model seems to be have no issues, and can be used in other modeling / data exchange operations.

testreadstep Prototype_IS.STP s
checkshape s s

Second, the artifacts (extra lines) that you see in 3D Viewer is a problem of Visualization part (which can be fixed, of course).
If you are not using Isoline presentation builder in application for some specific algorithm (usually you don't), there is no concert to it's issues save the visual artifacts on the screen.