# Is there any relevant content on CBCT system calibration in RTK？
**URL:** https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125
**Category:** Algorithms
**Created:** [August 3, 2023, 8:06am UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125 "2023-08-03T08:06:36Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@ma1282029525](https://discourse.itk.org/u/ma1282029525)
#### Post date: [August 3, 2023, 8:06am UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/1 "2023-08-03T08:06:37Z")
Recently, while studying CBCT calibration, I can only calculate the projection matrix from the position of the steel ball in one projection image and the mold. I can calculate a projection matrix for each projection image, but how can I combine multiple projection images to calculate?
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### Author:  [@simon.rit](https://discourse.itk.org/u/simon.rit)
#### Post date: [August 4, 2023, 12:49pm UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/2 "2023-08-04T12:49:42Z")
Sorry but I do not fully understand the question. There should be one projection matrix (and image) per source position. RTK’s geometry object, [rtk::ThreeDCircularProjectionGeometry](http://www.openrtk.org/Doxygen/classrtk_1_1ThreeDCircularProjectionGeometry.html) can store all them, simply use `AddProjection` for each one. How would you like to combine them?
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### Author:  [@ma1282029525](https://discourse.itk.org/u/ma1282029525)
#### Post date: [December 12, 2023, 7:27am UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/3 "2023-12-12T07:27:25Z")
What I want to know is how to obtain high-precision geometric information of my CBCT system. I have a set of 3D points and 2D projection points, and what should I do to obtain accurate circular geometric information
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### Author:  [@simon.rit](https://discourse.itk.org/u/simon.rit)
#### Post date: [December 12, 2023, 9:56am UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/4 "2023-12-12T09:56:15Z")
There is no such thing in RTK. You can probably estimate the projection matrix which minimizes the distance between projected 3D points and measured 2D points. That should not be too difficult.
Once you have estimated the projection matrix, you can use it with [AddProjection](http://www.openrtk.org/Doxygen/classrtk_1_1ThreeDCircularProjectionGeometry.html#aa02ca2d6285f6345c87d3b42d42e5a27).
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### Author:  [@ma1282029525](https://discourse.itk.org/u/ma1282029525)
#### Post date: [August 29, 2024, 3:44am UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/5 "2024-08-29T03:44:41Z")
When estimating, should each position be solved separately, or is it necessary to couple each angle together? Is it one equation set for each position, and then estimate a matrix this way?
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### Author:  [@simon.rit](https://discourse.itk.org/u/simon.rit)
#### Post date: [August 29, 2024, 4:13pm UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/6 "2024-08-29T16:13:57Z")
I haven’t implemented such a method myself and I’m sure there are several options. You can probably solve each position independently at first but you can also add some temporal constraints…
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### Author:  [@ma1282029525](https://discourse.itk.org/u/ma1282029525)
#### Post date: [August 30, 2024, 6:08am UTC](https://discourse.itk.org/t/is-there-any-relevant-content-on-cbct-system-calibration-in-rtk/6125/7 "2024-08-30T06:08:27Z")
ok thank you very much