Tile requests for GLCs to portable server should return 404 if no tile and outside of layer KML region

[tst-blaird]

Note that this issue is to change the behavior of portable server. There is a separate ticket to change the behavior of GEE server at #1578 .

Describe the bug

Tile requests to a layer in a GLC will return a tile even if there is no packet at the requested location. This causes imagery layers to be obscured in the GEE map viewer. The user can deselect the obscuring layer in the map viewer to see the other imagery layer.

I don't know the details but the server must be manufacturing a tile when no tile exists for the request. I suspect it's using a lower resolution tile and then extracting a section of that tile to satisfy the higher resolution request. If instead, the server did not return a tile then that might allow other imagery layers to show in the map viewer. To be honest I don't know what the map viewer would do with a 404 return from a tile request.

This new behavior should only happen if the request is outside the layer's KML region. If the request is for a tile that touches or is contained in the layer's KML region then the existing behavior should continue to be used.

Additionally, this new behavior should be specific to GLCs.

To Reproduce

Build GLMs of different areas. I used the SanFran tutorial data and USGS Orlando imagery. Assemble the two into a GLC and view the GLC in the GEE map viewer. It depends on the order of the layers but with both of them enabled one of them will be obscured. Deselect the imagery layer that is visible and the other will become visible.

Expected behavior

Both imagery layers should be visible in the map viewer without having to deselect one of them.

Desktop

• Server OS: Ubuntu 16
• Client OS: Windows 10
• Browser chrome
• Version 5.3.1

[tst-blaird]

Note that the same behavior can be observed with GLCs containing multiple globes. While testing a GLC containing two GLBs, one of the San Francisco tutorial imagery and the second of European imagery, I found that in the Earth Client I had to turn off the European imagery to be able to see the San Francisco imagery.