[MapProxy] Fixing or working around #583 (export using the existing image format of a source cache)?

[Johannes Kröger (WhereGroup)]

Hi there!

I recently discovered a bug with mapproxy-util export, where it would 
export tiles in the wrong format (PNG instead of JPEG): 
https://github.com/mapproxy/mapproxy/issues/583

Basically it seems that when there is a cache B, using another cache A 
as its source with the same grid, an export with mapproxy-util will 
ignore the image format defined for the cache B but instead blindly use 
the tiles from cache A.

There are some prior reports of similar issues, marked fixed already:
https://github.com/mapproxy/mapproxy/issues/94
https://github.com/mapproxy/mapproxy/issues/52

I might potentially get some capacity to look into this but would be 
fairly lost at first. Does someone have any pointers where one could 
start looking or how to most easily understand the concepts and code 
paths around this?

Alternatively, maybe there are some hacky workarounds. I wonder if I 
could specify another grid that is for all intents and purposes 
identical, not not identical to MapProxy, so that it would not lead to 
this issue? :> Another idea would be using seeding to a file instead of 
export but I'd like to avoid that approach for now (mostly because I am 
not sure if the issue would not happen there as well).

Cheers, Hannes

-- 
Johannes Kröger / GIS-Entwickler/-Berater

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