Retain internal mask while reprojecting

[drnextgis]

Internal mask is lost after reprojection rasters which are not loaded into memory. Possible ways to solve this solution: https://gist.github.com/drnextgis/ec24f73a895d8602a2d55d2b8d56bd3c

[astrojuanlu]

Great research @drnextgis! I would prefer not using sidecar files, I think it would complicate things too much. Between your options 2) and 3) I don't see a clear winner, so I would go for the simpler one.

As a more general question, do you think alpha bands are better supported than internal masks? I know internal masks give us the opportunity to use different masks per band, but it's not something that seems widely supported to me.