Cesium World Terrain does not render correctly in orthographic view modes

[argallegos]

Not sure if this is even something that would be feasible to support, but it looks like some tilesets (At least, Cesium World Terrain) don't render properly using the orthographic views. Here's a gif of how it's working from the Top orthographic view.

Note that the OSM buildings do not seem to be having the same issue, for some reason or another.

It's pretty much only rendering the tiles in the positive X direction, save for that one random one in the middle. The other orthographic views reinforce this. My guess is that it just doesn't know how to select which tiles to render in situations like this. If it's straightforward to add, this would be great to get working, since it's quite helpful to be able to line things up perfectly using the top or side orthographic view.

[argallegos]

@kring or @nithinp7 out of curiosity, is there a reason that this wasn't resolved with #547 being merged? I can confirm that the issue is still happening in version 1.8. I was expecting it would no longer be a problem but perhaps orthographic viewports are a different beast? Prompted by https://community.cesium.com/t/loading-tiles-in-top-down-view-in-unreal/16426

[nithinp7]

@argallegos Support for orthograhic viewports wasn't actually added in that PR, the actual orthographic frustum PR was never merged and is blocked by the open question of how to resolve SSE from geometric error for orthographic frustums. I came up with a possible way, but it runs the risk of loading or at least visiting way too many tiles during traversal. I'm not sure if it would have any further implications for how the traversal currently works. We haven't yet circled back and resolved any of those questions.

[argallegos]

Got it, thanks for the update! Didn't think to check for a PR in Cesium Native.

[argallegos]

In the meantime, you can use this workaround identified by the forum user I linked above.

Open a second viewport that faces the region that you wish to see in the orthographic view. This should force the tiles to load.