# about AddProjection(const HomogeneousProjectionMatrixType & pMat)

**URL:** https://discourse.itk.org/t/about-addprojection-const-homogeneousprojectionmatrixtype-pmat/7232
**Category:** Algorithms
**Tags:** rtk
**Created:** [September 24, 2024, 9:23am UTC](https://discourse.itk.org/t/about-addprojection-const-homogeneousprojectionmatrixtype-pmat/7232 "2024-09-24T09:23:48Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![ma1282029525](https://discourse.itk.org/user_avatar/discourse.itk.org/ma1282029525/32/3084_2.png) [@ma1282029525](https://discourse.itk.org/u/ma1282029525)
#### Post date: [September 24, 2024, 9:23am UTC](https://discourse.itk.org/t/about-addprojection-const-homogeneousprojectionmatrixtype-pmat/7232/1 "2024-09-24T09:23:48Z")

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WARNING: In D:\rtk\RTK-2.4.1\src\rtkThreeDCircularProjectionGeometry.cxx, line 358  
DataObject (000001DBC37F0C40): Failed to AddProjection

What does this error mean?

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### Author: ![dzenanz](https://discourse.itk.org/user_avatar/discourse.itk.org/dzenanz/32/1093_2.png) [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [September 24, 2024, 12:08pm UTC](https://discourse.itk.org/t/about-addprojection-const-homogeneousprojectionmatrixtype-pmat/7232/2 "2024-09-24T12:08:25Z")

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@simon.rit might know.

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### Author: ![simon.rit](https://discourse.itk.org/letter_avatar_proxy/v4/letter/s/f08c70/32.png) [@simon.rit](https://discourse.itk.org/u/simon.rit)
#### Post date: [September 24, 2024, 12:18pm UTC](https://discourse.itk.org/t/about-addprojection-const-homogeneousprojectionmatrixtype-pmat/7232/3 "2024-09-24T12:18:41Z")

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It means that it did not manage to convert the projection matrix to meaningful parameters for the reconstruction. You can check the code if you’d like to know. The reason is a failure to convert the rotation matrix to angles (see [here](https://github.com/RTKConsortium/RTK/blob/master/src/rtkThreeDCircularProjectionGeometry.cxx#L294-L309) and [here](https://github.com/RTKConsortium/RTK/blob/master/src/rtkThreeDCircularProjectionGeometry.cxx#L350-L360)).