updated comments.  verified snap function is correct.  verified locations function is correct.  both need tests
updated comments.  verified snap function is correct.  verified locations function is correct.  both need tests


Former-commit-id: 8ccf60ce199ba04fb60a41670e5755f52b5e9713
USGS-EROS/lcmap-firebird,USGS-EROS/lcmap-firebird