“Optimize Cameras” increased the RMS reprojection error.

[Ryuseiken]

In PhotoScan 1.3.1, I have witnessed an increase in “RMS reprojection error” (in the tie point scale) by running “Optimize Cameras” even though there’s no markers and/or camera extrinsic parameters provided.

Could you tell me why this happens?

The detailed situation is as follows.

After loading the images, I ran “Align Photos” with adaptive camera model fitting, and the resultant “RMS reprojection error” (in the tie point scale) 0.0437678. No camera intrinsic parameter changed from the initial value at this stage. This is not strange because in the adaptive mode PhotoScan can judge that estimating any  intrinsic parameter would be unstable.

Then, I ran “Optimize Cameras” allowing only “f” to change. The resultant “RMS reprojection error” was 0.0519948, larger than the value before the optimization. According to the user manual, the target function of this optimization command is “RMS reprojection error” + “reference coordinate misalignment.”
In this case, no markers and no camera position/rotation information were provided, and therefore, simply “RMS reprojection error” should be minimized.