# Thickness analysis of a solid sheet metal
**URL:** https://discourse.vtk.org/t/thickness-analysis-of-a-solid-sheet-metal/3341
**Category:** Support
**Created:** [May 19, 2020, 1:52pm UTC](https://discourse.vtk.org/t/thickness-analysis-of-a-solid-sheet-metal/3341 "2020-05-19T13:52:48Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@DFlyer](https://discourse.vtk.org/u/DFlyer)
#### Post date: [May 19, 2020, 1:52pm UTC](https://discourse.vtk.org/t/thickness-analysis-of-a-solid-sheet-metal/3341/1 "2020-05-19T13:52:48Z")
I have a CAD solid sheet metal part, I can mesh them to surface or volume elements. Is there a technique to extract the midsurface in VTK? Also is it possible to estimate thickness from the computed mid surface?
The main objective is to perform thickness analysis, so it may not necessary calculate midsurface, any method that provides thickness would be great!
Thanks.
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### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [May 20, 2020, 12:26am UTC](https://discourse.vtk.org/t/thickness-analysis-of-a-solid-sheet-metal/3341/2 "2020-05-20T00:26:12Z")
Medial surface extraction is a hard problem. If you had the information in your CAD system then export it from there instead of trying to reconstruct from an exported surface mesh.
Anyway, if you don’t have any other option, you can use `vtkvmtkPolyDataCenterlines` in the VTK-based [VMTK toolkit](https://github.com/vmtk/vmtk) to get medial surface (returned by `GetVoronoiDiagram`). I think the Voronoi polydata already contains thickness values in a point scalar.
Alternatively, you can convert the polydata to a fine-resolution binary image using polydata to stencil filter, then use ITK filters to get the medial surface, compute a distance map from the skeleton, and sample that with a VTK probe filter. See a complete example for this approach here: [https://discourse.slicer.org/t/how-to-analyze-the-thickness-of-the-model/2735](https://discourse.slicer.org/t/how-to-analyze-the-thickness-of-the-model/2735)