# Ftheta model parameters

**URL:** <https://forums.developer.nvidia.com/t/ftheta-model-parameters/156684>\
**Category:** DRIVE AGX Xavier General\
**Tags:** driveworks-calibration, camera\
**Created:** [October 9, 2020, 10:06am UTC](https://forums.developer.nvidia.com/t/ftheta-model-parameters/156684 "2020-10-09T10:06:09Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![vzadrijaRA](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@vzadrijaRA](https://forums.developer.nvidia.com/u/vzadrijaRA)\
**Post date:** [October 9, 2020, 10:06am UTC](https://forums.developer.nvidia.com/t/ftheta-model-parameters/156684/1 "2020-10-09T10:06:09Z")

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The documentation does not provide any details for the ftheta camera model.  
This [post](https://forums.developer.nvidia.com/t/documentation-on-ftheta-camera-model/81882) states that it is actually the Kannala-Brandt generic camera model. The Kannala-Brandt model specifies the forward projection parameters in a form: [`k1, k2, fu, fv, u0, v0, ....`]

The `dwFThetaCameraConfig` structure specifies the back projection polynomial: `backwardsPoly` and the center of projection (`u0`, `v0`)

**Question** :

1. What is the meaning of `backwardsPoly` coefficients?
2. Which coefficients correspond to the “focal lengths” `fu` and `fv` from the Kannala-Brandt model?

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**Author:** ![SivaRamaKrishnaNV](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/sivaramakrishnanv/32/14043_2.png) [@SivaRamaKrishnaNV](https://forums.developer.nvidia.com/u/SivaRamaKrishnaNV)\
**Post date:** [October 12, 2020, 8:00am UTC](https://forums.developer.nvidia.com/t/ftheta-model-parameters/156684/3 "2020-10-12T08:00:58Z")

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Dear @vzadrijaRA,  
I am checking internally and get back to you.

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**Author:** ![SivaRamaKrishnaNV](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/sivaramakrishnanv/32/14043_2.png) [@SivaRamaKrishnaNV](https://forums.developer.nvidia.com/u/SivaRamaKrishnaNV)\
**Post date:** [October 13, 2020, 5:39am UTC](https://forums.developer.nvidia.com/t/ftheta-model-parameters/156684/6 "2020-10-13T05:39:28Z")

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Dear @vzadrijaRA,  
I am attaching white paper on Ftheta model. We are looking to improve our documentation as well on this. Thank you for brining to our notice.  
[ftheta.pdf](https://forums.developer.nvidia.com/uploads/short-url/bs3RR5Ldd7i5VCjHIcryEDzrMAh.pdf) (87.0 KB)

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**Author:** ![TomNVIDIA](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/tomnvidia/32/14181_2.png) [@TomNVIDIA](https://forums.developer.nvidia.com/u/TomNVIDIA)\
**Post date:** [October 12, 2021, 8:04pm UTC](https://forums.developer.nvidia.com/t/ftheta-model-parameters/156684/8 "2021-10-12T20:04:25Z")

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