# Hello. I got problem on the geometry for vtk.

**URL:** <https://discourse.vtk.org/t/hello-i-got-problem-on-the-geometry-for-vtk/874>\
**Category:** Development\
**Created:** [April 30, 2019, 7:48am UTC](https://discourse.vtk.org/t/hello-i-got-problem-on-the-geometry-for-vtk/874 "2019-04-30T07:48:28Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![David](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/d/aeb1de/32.png) [@David](https://discourse.vtk.org/u/David)\
**Post date:** [April 30, 2019, 7:48am UTC](https://discourse.vtk.org/t/hello-i-got-problem-on-the-geometry-for-vtk/874/1 "2019-04-30T07:48:28Z")

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I did Volume rendering my CT by using vtkSmartVolumeMapper , and  
did Modeling on same CT by using vtkMarchingCubes.

But the Geometry of between Volume rendering and Modeling is different.  
I attach the picture for the different Geometry.  
Why did it occur? In addition, how can I match the geometry?

I cannot keep going, now.

Could you help me?

Thank you~~

 ![1](https://discourse.vtk.org/uploads/default/original/1X/ae098e47dd678c988c3c49f246cf6f4c885138bb.jpeg)

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**Author:** ![lassoan](https://discourse.vtk.org/user_avatar/discourse.vtk.org/lassoan/32/50_2.png) [@lassoan](https://discourse.vtk.org/u/lassoan)\
**Post date:** [April 30, 2019, 12:51pm UTC](https://discourse.vtk.org/t/hello-i-got-problem-on-the-geometry-for-vtk/874/2 "2019-04-30T12:51:16Z")

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I can barely see anything from your volume rendering. Enable shading and adjust volume rendering transfer functions so that we can see something.

Surface and volume rendering only provide similar results if the volume rendering scalar opacity function is a step function, and the step position matches the contour filter’s iso-value.