Tile cache keys collide for overlapping imagery (we think)

[jisantuc]

Problem description

When imagery overlaps and the tile cache is enabled, a weird visual artifact occurs where the scene coloring stops respecting what you ask for, and weird gaps show up in the imagery. It's not totally clear why this is the case, but we know it has something to do with the cache, which normally means something to do with cache keys.

Here's the problem with several overlapping scenes:

However, there's a similar bad problem when you just have one scene (though this scene is also one of the scenes in the multiple scenes, so I don't know if there's contamination somehow):

Replication Steps

• get some overlapping S2 imagery (see azavea/raster-foundry-platform#829 for some links)
• load it up locally
• add it to the same project
• try to visualize it
• zoom around and change color modes

Expected Behavior or Output

Caching should Just Work ™️

Acceptance criteria for closing this if the issue is verified to be a cache key collision are:

• it's demoable and fixed
• there's a test that for BacksplashImages with the attributes in question, generating the cache key is different for:
  • the same zoom and two different color corrections
  • the same color correction params and two different zooms