Available images restricted to perimeter

Available images are currently restricted to the screen extent. Meaning that image tiles are made available that don't intersect with the fire perimeter. Would like to have these filtered out to just ones that intersect with the fire perimeter

No files, tests, or entry points are named in the issue. Start by tracing where available image tiles are selected from the screen extent, then identify how the fire perimeter is represented and used. Done means tiles that do not intersect the fire perimeter are excluded while intersecting tiles remain available.

Written by the indexing model from the issue text.