Hello all,

I previously made a post asking for help with layers and masks, regarding terrain building, but I have figured out most of what I needed to know. At this point, I want to get your advice on how I should go about making a satellite mask layer for a satellite image that I got from ArcGIS.

The method I have been using thus far uses GIMP and the path tool. I am tracing the green grass areas with a fill color (255,255,0) and so forth. Essentially, I am creating the mask layers by hand. However, the map is enormous (15360x15360) so this process is taking ages. Is there an easier way to create a mask with the satellite texture I extracted from ArcGIS?

I've seen a lot of guys generate pre-made terrains with L3DT, which does all of this for you, but I haven't seen much examples of real world terrain masks. Any help would be greatly appreciated guys!