Setting the src_id baed on the resolution

[bokhaeng]

Setting the src_id baed on the resolution and it will need to be 12_1, 9_1, or 3_1 depending on the grid size per the approach in table A-2

[cseppan]

Commit ac4c4f3 adds an optional environment variable named GRID_PREFIX to set the resolution for nonpt, nonroad, np_oilgas, and rwc. Example usage:

export GRID_PREFIX=9_

If GRID_PREFIX isn't set, nonpt, nonroad, and rwc default to "12_", and np_oilgas defaults to "4_".