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Author Topic: Camera Calibration and Distortion Plot  (Read 2232 times)

dcobra

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Camera Calibration and Distortion Plot
« on: March 07, 2019, 11:27:17 PM »
Hello,

I've been experimenting with camera calibration parameters and have processed a model with two different configurations.  The configurations are as follows:
1 - F, Cx, Cy, B1, B2, K1, K2, K3, K4, P1, P2
2 - F, Cx, Cy, B1, B2, K1, K2, K3, K4, P1, P2, P3, P4

These two configurations give quite different distortion plot results and I am trying to understand the meaning of them (see image attached).  The first distortion plot seems quite realistic, increasing distortion with increasing radius.  The second distortion plots looks odd, but gives better RMSE on check points, and there is lower distortion in the decentering plot.  Is the second plot realistic?  Or is it a case of over parameterization? Any advice you have is appreciated.

JMR

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Re: Camera Calibration and Distortion Plot
« Reply #1 on: March 08, 2019, 11:45:26 AM »
I guess the second graph looks weird because the vertical axis is unsigned, so try to imagine the second hump upside down and you will see it is not-so-odd. Also note that the vertical scale is rather smaller, decentering abs values are smaller in the second plot, so actual decentering distortion might be overestimated when using less parameters, so adding P3, P4 could actually make sense.

dcobra

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Re: Camera Calibration and Distortion Plot
« Reply #2 on: March 08, 2019, 01:57:06 PM »
JMR,

Thanks for the reply.  I think you are right, the vertical axis being unsigned is what is making it look so odd.  Including P3 and P4 do appear to improve the model based on a few observations: 1) lower control to check point RMSE ratio and 2) more randomly orientated and lower image residuals, although there is greater correlation between parameters when included (see image attached).