Checkerboard configuration - enforce consistent orientation by warning if (rows < cols)

[schneith]

See https://groups.google.com/forum/#!topic/kalibr-users/wYt0uhedT4Y

[goldbattle]

Hi Thomas,

This was actually a false alarm... The problem was in calibration_target.yaml.
I had erroneously written 8 rows and 6 columns for the checkerboard, instead of
6 rows and 8 columns. This change fixed everything and I do not get divergence
any more.

Maybe you can include a simple warning in the code that checks #rows < #cols for
checkerboards when the yaml files are read.

Thanks,
Florian