possibly cache things like validPixels

[esheldon]

clear the cache when the map is modified, e.g. by oring it with another etc.

[erykoff]

Good idea.

[erykoff]

I've looked into this, and with large high res maps it potentially increases the memory usage by a significant amount (e.g., the user would know whether they want to cache or not). At the same time, I significantly improved the speed of computing valid_pixels. Is this still thought to be necessary?

[kadrlica]

Calculating the valid_pixels of a wide map is still pretty time and memory intensive.