# vtkPyramid / vtkQuadraticPyramid Inconsistencies

**URL:** https://discourse.vtk.org/t/vtkpyramid-vtkquadraticpyramid-inconsistencies/931
**Category:** Support
**Created:** [May 8, 2019, 11:49am UTC](https://discourse.vtk.org/t/vtkpyramid-vtkquadraticpyramid-inconsistencies/931 "2019-05-08T11:49:53Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![andreas](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://discourse.vtk.org/u/andreas)
#### Post date: [May 8, 2019, 11:49am UTC](https://discourse.vtk.org/t/vtkpyramid-vtkquadraticpyramid-inconsistencies/931/1 "2019-05-08T11:49:53Z")

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Hi Folks,

I’ve got some questions regarding the pyramidal elements in vtk:

1. First of all: Why is the GetParametricCenter() different in both cells, although they span the same domain:

Wouldn’t I expect that both cells have the same parametric center?

1. Regarding the EvaluatePosition() method:  
If I look at how the initial position is chosen

I wonder even more:

- Why is the linear initial position set to 1./3. instead of the parametric center?
- Why is the quadratic initial position set to 0.5 instead of the parametric center? Here I wonder even more because it looks like this point is located on the surface instead of the interior, correct?

Thanks for the help.