I had something happen today (build 1847) that I never saw before.

I started with an older project that was divided in chunks. Merged the chunks and added more GCPs. saved project and exported markers. To get rid of duplicate images I opened an even older version without chunks or GCPs and imported markers and camera calibration then realigned (after making sure GCPs were marked on all images).

After realignment I trimmed all of the flyers and sinkers in my sparse point cloud, then did an optimization step. Instead of seeing the standard "bundle_adjust: xxxxx.." text I saw text that looked like this:

"matrix_invert: singular matrix

xxmatrix_invert: singular matrix.."

etc until bundle adjust was complete. That was weird. So I looked at my biggest GCP offset, which didn't seem too bad, and edited a few points, then did another bundle adjust. That one looked normal. But what the heck is "matrix invert: singular matrix" ?

relevant logfile text follows (from original bundle adjust and bundle adjust #2):

`Optimizing point cloud...`

weights: 35.9691 cameras, 71938.1 markers, 359691 scalebars, 40 projections

bundle_adjust: matrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxxxmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xxxxmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

xxmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xxxxxmatrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

matrix_invert: singular matrix

xxx 50.0073 -> 1.24502

finished SBA in 303.487 seconds

Finished processing in 304.394 sec (exit code 1)

disabled 2 points

Optimizing point cloud...

weights: 35.9691 cameras, 71938.1 markers, 359691 scalebars, 40 projections

bundle_adjust: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 1.26989 -> 1.21925

finished SBA in 389.478 seconds