Curved placement of downward faced cameras

[Casper_H]

Hi,

Issue:
I have a problem with the alignment when using cameras fixed on a rig, facing directly downward. The camera's taken under an angle are aligning correctly, but when i use the downward facing photos, the cameras and the model get curved. I did not remove any EXIF data or altered the lensprofile externally.

Object:
The object is a city maquette, approx. 70 x 90 cm.

Lens/Camera used:
I use a fixed 30 mm lens (Sigma C) on a APS-C sony body (A6500).

Driver/OS versions:
Windows: 1903
GPU (nvidia): 431.6

Anyone any idea what causes this and how to fix it?

Greetings, Casper

[Alexey Pasumansky]

Hello Casper,

Are the images taken vertically and with the angle calibrated in the same group (see Camera Calibration dialog)? If yes, then I can suggest to split the calibration groups in order to have each group be corresponding to only single flight. After that optimize the alignment using all the available parameters except K4, P3 and P4 (unless any of these three are already checked on by default).

If the problem persists, please provide the screenshots of the Adjusted calibration values for each group.

[Casper_H]

Thanks, Alexey, that worked!

Just for thread completion's sake, i've added a screenshot of the correctly aligned model and overview of the camera calibration groups.

One question though: is making camera calibration groups for each camera placing always advisable, even when the camera lens is fixed and the settings are unaltered?

[Alexey Pasumansky]

Hello Casper,

For consumer grade digital cameras (opposed to professional class camera+lens system) the calibration parameters may vary along with the optic system parameters due to temperature variance, for example. Also landing and take-off process may affect them due to possible mechanical effect.

[Casper_H]

Hello Alexey, thank you for the good explanation. I'll keep in mind to make calibration groups more quickly.