Generated cache cannot be loaded by Cesium while served from webserver

[Sgambe33]

I tried using this tool to generate offline tiles to then serve with a webserver because I do not have the possibility of running a server 24/7 with the necessary computing power to generate tiles on the go. I noticed that some tiles are missing since CesiumJS throws some errors about being "unable to load terrain tile": Failed to obtain terrain tile X: 541 Y: 123 Level: 9. Error message: "Request has failed. Status Code: 404" Keep in mind that when seeding the cache I specifically choose all zoom layers from 0 to 17. Is this problem related to this program or some kind of misconfiguration on my end?

Furthermore, just a curiosity, why are tiles generated by this progam way smaller than the ones created by CesiumIon? Like for the same dataset cotd's are about 30mb while Ion's are 400mb.

[tebben]

Did you use the seed-cache script to generate the cache? If so did it gave you any error or is there a file /9/541/123.terrain in the directory?

If the COG you are using is available somewhere I could have a look later this week.

I'm not sure why it's 30MB vs ION's 400MB, maybe there were errors/problems and not all tiles are generated or maybe ION tiles further than level 17 which can increase the size by a lot.

[Sgambe33]

I looked again and that tile is present but now I get another error for level 0: Failed to obtain terrain tile X: 1 Y: 0 Level: 0. Error message: "TypeError: Cannot read properties of undefined (reading 'computeChildMaskForTile')" If you need the COG I can send it to you.

[tebben]

Cesium requests a terrain tile with an inverted y compared to the TMS, the cache in CTOD stores and loads tiles according to the TMS schema. In the latest update the cache now follows the inverted y structure so the cache can be served directly without CTOD in between.

the seed_cache script now also contains a new option --export-layer-json {max_zoom} to create a layer.json in the root directory of the tiles layer_code/meshing_method/layer.json. Add an integer to --export-layer-json to define the max zoom level Cesium will request.

I didn't get the same error you described above with the old cache but I hope this update solves your problem.

I tested the following:

Generate cache

poetry run seed_cache --port 5001 -m grid -i ./ctod/files/test_cog.tif -o ./cache-test -r 20 -z 0-1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17 --export-layer-json 17

Serve cache

cd cache-test/{layer_id}/grid
http-server -p 3000 -g --cors

View

Within a simple self hosted html file with Cesium I set the terrain provider to http://localhost:3000 and it showed me the terrain from hosted cache directory correctly without warnings in the developer console.

[Sgambe33]

Thanks for the quick fix! Everything seems to be working fine now. Still thinking about the size difference, could it be the method used for generating the tiles?

[tebben]

No problem.

Yes, there can be a size difference because of the method used and thus the amount of vertices in a tile. ION probably uses something similar to delatin which is likely smaller in size compared to the grid method unless there is a huge hight difference. Maybe i'll have a look later creating terrain tiles using ION and compare them to tile generated with CTOD.

Closing the issue since it's fixed.