Try functionalities "diff" and "patch"

[MichaelKreil]

If we produce new tiles from a new planet dump, probably only a small percentage of tiles have changed. Maybe adding a command "diff" to extract only changed tiles and "patch" to update tiles might help keeping a planet.versatiles file up to date more easily.

[MichaelKreil]

Something like this could be used to merge multiple sources:

versatiles patch in1.versatiles in2.versatiles in3.versatiles out.versatiles

Alternative names for this sub command could be: add, merge, stack, paste, overlay, overwrite, flatten, composite, ...

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Or we go in the direction of a "virtual sources" like:

versatiles convert "merge:in1.versatiles,in2.versatiles,in3.versatiles" out.versatiles

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This would also solve: versatiles-org/versatiles-generator#6