When checking for bad indices, the following assertion fails when reading survey data that contains -1 values:
I don't really understand the implications, but I bypassed the issue by allowing -1 as a valid value:
in_skim = (mapped_orig >= -1) & (mapped_orig < self.omx_shape[0]) & \
(mapped_dest >= -1) & (mapped_dest < self.omx_shape[1])