# coincident topology offset parameters
**URL:** https://discourse.vtk.org/t/coincident-topology-offset-parameters/4836
**Category:** Support
**Created:** [December 16, 2020, 4:36pm UTC](https://discourse.vtk.org/t/coincident-topology-offset-parameters/4836 "2020-12-16T16:36:31Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@andreasbuykx](https://discourse.vtk.org/u/andreasbuykx)
#### Post date: [December 16, 2020, 4:36pm UTC](https://discourse.vtk.org/t/coincident-topology-offset-parameters/4836/1 "2020-12-16T16:36:31Z")
I am working on migrating our FEA application from VTK 8.1.1 to VTK 9.0.1. As a
result of the changes to how coincident topology resolution is implemented I
get a lot of changes. sometimes they are improvements but unfortunately often
they are not, and I am struggling to determine an good approach for choosing
new values.
Let me first illustrate for what purposes we use the relative factors:
- draw selected or highlighted dots/lines over existing mesh
- draw selected or highlighted faces transparently over existing mesh
- draw edges in front of mesh faces
- draw glyphs in front of faces, edges and vertices
- draw line elements in front of surfaces and surface edges in 2D view
All of these aspects are represented by different actors (typically also
separate actors for faces, lines and vertices) to give full control over
opacity, line and point thickness and relative offsets among others.
I would very much appreciate some explanation of how the relative offset
parameter values are used by the mappers in VTK 9.0.1, or some guidance in
choosing suitable parameters to approximate the behavior in VTK 8.1.1.
Thank you very much for your help.
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### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [December 16, 2020, 10:36pm UTC](https://discourse.vtk.org/t/coincident-topology-offset-parameters/4836/2 "2020-12-16T22:36:15Z")
These VTK changes broke many things in 3D Slicer, too. We have been struggling for several weeks trying to fix these, but I’m still not sure if it is possible without reverting these invasive changes in VTK or redesigning our application (so that we use coincident topology resolution for trivial things).
@sankhesh has been a great help in this, maybe he can provide a bit more details.
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### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [December 21, 2020, 5:17pm UTC](https://discourse.vtk.org/t/coincident-topology-offset-parameters/4836/3 "2020-12-21T17:17:25Z")
@andreasbuykx @lassoan I have some in-progress changes in the VTK coincident topology resolution code that should alleviate some of these issues. See [https://gitlab.kitware.com/vtk/vtk/-/merge\_requests/7480](https://gitlab.kitware.com/vtk/vtk/-/merge_requests/7480)