Identifying "bad" data

[Doug Welch <welch@physics.mcmaster.ca>]

By far the best way to identify the major reasons for discrepant points
is to examine the images. I have been nibbling away at a scheme for 
storing 10x compressed (lossy) images for quick retrieval and
examination. Even extracting random sections of images reveals many
instances of artifacts which must result in bad photometric points
on occasion. Tom is right that there are *many* planes which fly through
his fields each night!

Cheers,
Doug