tile scheme

[ltclm]

why is our tile adressing scheme different from the default tms scheme described here:
http://www.maptiler.org/google-maps-coordinates-tile-bounds-projection/

The viewer on this page shows the last tile which fully contains switzerland has the address:
TMS: 6,33,41
Google: 6,33,22

In our scheme the corresponding tile has the address: 5,33,7
i know the y value in the cesium debug mode is wrong (top left origin instead of bottom left origin).
Where is the offset in the z-value coming from?

[gjn]

AFAIK, we take our pyramid for global_geodetic, which is taken from gdal: https://github.com/geoadmin/3d-forge/blob/master/forge/lib/global_geodetic.py

[loicgasser]

AFAIK Google is using spherical mercator (EPSG 900913) with WGS84 datum, so projected on a sphere rather than a ellipsoid like we do with EPSG:4326. We can acutally generate both, we just need to change the tiling scheme.

[loicgasser]

Sorry misread the question. For y it is apparently a cesium issue: https://github.com/geoadmin/3d-testapp/pull/7
For z we start at 0 they start at 1 I guess.

[thiloSchlemmer]

Hi there.
i'm trying to produce quantized-mesh tiles and deliver the tiles with geo-data/cesium-terrain-server.
But i stumble over the tiling scheme in cesium. i saw, that the file 3d-forge/configs/terrain/layer.json uses the before mentioned different tiling scheme. Why is the y-value different to TMS and Google? Is there a way to transform from TMS?

[loicgasser]

Actually TMS specifications put the origin at the bottom left and not at top left like Google.
Starting with 2 tiles at beginning, you see it for yourself here :
https://wiki.osgeo.org/wiki/Tile_Map_Service_Specification#global-geodetic

Cesium seems to implement exactly this spec per defaut with y pointing up. You can use the GlobalGeodetic class in this project to generate the grid or use directly the one in quantized-mesh-tile library.

You can use the GlobalGeodetic
https://quantized-mesh-tile.readthedocs.io/en/latest/tutorial.html#read-a-local-terrain-tile
Or via mapproxy or even this pypi module
https://github.com/geoadmin/gatilegrid
(you can choose y pointing down or up)

The layers.json file is used to restrict the extent of your terrain and configure the tile adresses. It can be generated using
https://github.com/geoadmin/3d-forge/blob/master/forge/layers/metadata.py

And
https://github.com/geoadmin/3d-forge/blob/master/forge/scripts/tilejson_writer.py
(that is if you store your tiles in s3)