# Is there a way to detect feature points of volume(vtkImageData) like in mesh(vtkPolyData)?

**URL:** <https://discourse.vtk.org/t/is-there-a-way-to-detect-feature-points-of-volume-vtkimagedata-like-in-mesh-vtkpolydata/12730>\
**Category:** Development\
**Created:** [November 16, 2023, 9:55am UTC](https://discourse.vtk.org/t/is-there-a-way-to-detect-feature-points-of-volume-vtkimagedata-like-in-mesh-vtkpolydata/12730 "2023-11-16T09:55:11Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![gongwaner](https://discourse.vtk.org/user_avatar/discourse.vtk.org/gongwaner/32/6996_2.png) [@gongwaner](https://discourse.vtk.org/u/gongwaner)\
**Post date:** [November 16, 2023, 9:55am UTC](https://discourse.vtk.org/t/is-there-a-way-to-detect-feature-points-of-volume-vtkimagedata-like-in-mesh-vtkpolydata/12730/1 "2023-11-16T09:55:11Z")

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Hi guys,  
I’m trying to detect feature points from given input imagedata. More specifically, given CT scan of an object with visually-obvious concave and concave parts, return concave points and convex points.

The only way I can think of doing this is by:  
1.convert imagedata to polydata using marching cube(given isovalue)  
2.detect feature points using polydata. specifically, for concave/convex points, I can use curvature filter and easily find these feature points.

This is doable.The problem is that I lose precision during conversion from imagedata to polydata.  
I don’t think I can calculate the curvature of imagedata, is it possible to detect concave/convex feature on imagedata itself?

Thanks!