Question on missing assets for mosaic.json

[kmcruickshank]

Hi there,

I have been experimenting with Titiler to serve out map tiles from 4 COGs which I access through a mosaic.json file. I am able to display the tiles correctly in a basic web application, but I keep getting the following within the Titiler server console log:

raise NoAssetFoundError(f"No assets found for tile {z}-{x}-{y}") cogeo_mosaic.errors.NoAssetFoundError: No assets found for tile 13-4542-4934

I have checked the specific tiles being requested and can confirm they fall outside of my COGs extent. I'm just not sure if I should be receiving these exceptions at all if the mosaic.json were functioning correctly. Perhaps I have made an error in the preparation of my data?

Some more info. The base COGs are in EPSG:6933, with the COG tiling being created with rio-cogeo using the -w parameter for web tiling (my understanding is that it creates tiles that conforms to web mercator). I have configured Titiler with the MosaicTilerFactory route, which I then access the tiles using the WebMercatorQuad TileMatrixSet. Could you provide some guidance as I've read through all of the Titiler documentation and have searched through the discussions and cannot find anyone reporting this issue.

[vincentsarago]

Hi @kmcruickshank

I think the issue comes from the client application requesting those tiles. If the client (e.g leaflet) has the bounds of the mosaic (e.g when you request a tilejson.json document there should be the bounds which cover the 4 COG) it should not try to fetch for tiles that are not within the bounds.

Another potential issue is that at high zoom level a Tile could be within the Mosaic BBOX but will not have any associated asset 👇

[kmcruickshank]

Hi @vincentsarago,

Thanks for the reply, this seems consistent with what is happening on my setup. Just to confirm, for the cases where I have 'Tile within the mosaic bbox but with no asset', should I be expecting the server to produce a '500 Internal Server Error'? Is it fine to ignore these errors or is there a better way to handle the error when it arises?

[vincentsarago]

should I be expecting the server to produce a '500 Internal Server Error'? Is it fine to ignore these errors or is there a better way to handle the error when it arises?

It depends if your titiler application has the correct error handler set

titiler/src/titiler/application/titiler/application/main.py

Line 198 in 08868e5

add_exception_handlers(app, MOSAIC_STATUS_CODES)

titiler/src/titiler/mosaic/titiler/mosaic/errors.py

Line 16 in 08868e5

NoAssetFoundError: status.HTTP_204_NO_CONTENT,

[kmcruickshank]

Thank you @vincentsarago, the references to the handlers assisted with my problem. All working well now.