TMS tile providers: negative {-y} in urls

[abubelinha]

Basically all this is already described in geopandas/xyzservices#177

I found some tile servers in these pages and I was trying to use them in contextily:

https://www.ign.es/web/ide-area-nodo-ide-ign
https://idee.es/en/servicios-teselas

I am guessing there is a problem with xyz syntax since their urls end in {z}/{x}/{-y}.extension
Not sure how to implement that in my code:

import contextily as cx
# gdf is a simple geodataframe of a 10 x 10 Km square polygon inside Spain
ax = gdf.plot(figsize=(10, 10), alpha=0.05, edgecolor="k")
# this works well for my area:
tile_source = cx.providers.OpenStreetMap.Mapnik  
tile_attribution = 'OSM contributors' 
# but this fails:
tile_source='https://tms-pnoa-ma.idee.es/1.0.0/pnoa-ma/{z}/{x}/-{y}.jpeg'  
tile_attribution = 'idee.es pnoa-ma'
cx.add_basemap(ax=ax, crs='epsg:4326', source=tile_source, attribution=tile_attribution)
plt.savefig('contextily_test.png', bbox_inches='tight')

Thanks for any help
@abubelinha

EDIT: some related links?

• https://blog-idee.blogspot.com/2022/01/servicios-xyz-de-teselas-raster.html
• https://gis.stackexchange.com/questions/300336/updated-can-tms-convention-xyz-tiles-be-displayed-in-qgis-3-4
• https://alastaira.wordpress.com/2011/07/06/converting-tms-tile-coordinates-to-googlebingosm-tile-coordinates/
• @tmcw xyz_vs_tms.md (The difference between XYZ and TMS tiles and how to convert between them)

[abubelinha]

I was able to got this to work touching some tile.py lines in my installed package.

I basically look for a '{-y}' string in source url.
If that substring exists, I reconstruct the tiles array in both bounds2img() and _merge_tiles() in order to correct y values using the formula provided by @tmcw here:
https://gist.github.com/tmcw/4954720

This is probably not the best way to do it but I am happy to share my code so an expert can tell if there is something reusable in it or this should be implemented in a very different way.
Sorry I am not a git user.
Would it be enough if I clone the repo, edit the file and share a link here, so someone else can test it?

[martinfleis]

Would it be enough if I clone the repo, edit the file and share a link here, so someone else can test it?

Yeah, that would help!

[abubelinha]

I uploaed my modified tile.py here:
https://github.com/abubelinha/contextily/commits/inverted_y_sources/contextily/tile.py

But when I compared lines changed, I realized I was not using the last version published in github:
I edited the pip-installed version (1.5.2) instead.

I later tried to install development version from github, but I couldn't:

C:\Python38\scripts\pip install https://github.com/geopandas/contextily/archive/master.zip
Collecting https://github.com/geopandas/contextily/archive/master.zip
  Using cached https://github.com/geopandas/contextily/archive/master.zip
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error

  × Getting requirements to build wheel did not run successfully.
  ¦ exit code: 1
      LookupError: setuptools-scm was unable to detect version for C:\Users\abu\AppData\Local\Temp\pip-req-build-mexwnes2.

      Make sure you're either building from a fully intact git repository or PyPI tarballs. Most other sources (such as GitHub's tarballs, a git checkout without the .git folder) don't contain the necessary metadata and will not work.

      For example, if you're using pip, instead of https://github.com/user/proj/archive/master.zip use git+https://github.com/user/proj.git#egg=proj
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.

I hope differences are not important and you can test my changes (I only touched a couple of functions and added a new one).

In my commit I also added (as a commit-comment) a contextily_tms_test() function to test my changes using a given server, zoom and bounding box coordinates to generate a image.

I couldn't find yet any global coverage mapping service which also uses flipped '{-y}' tiles and reaches high zoom levels (i.e. 14 or higher). So my examples are only from the Spanish services I posted above and I guess they will fail to serve tiles outside Spain unless you use big bounding boxes to force small zoom levels.

Please test it using other flipped-Y servers that you know

[martinfleis]

This is all eventually related to #120 which was never finished.

[abubelinha]

No idea, but IMHO my issue is much simpler.

Just a matter of correcting y values when servers use an inverted tile numbering system for y axis

[Ralph-UP]

I had the same problem with self generated tiles using „gdal2tiles“ from an GeoPDF source — one other solution is simply to regenerate the tiles with WMS naming.

After working with the patch, solution proposed by @abubelinha, I came up with a much shorter solution, at least for my case:

• I created a subclass TMSTileProivder from xyzservices.TileProvider and simply perform the „invert y“ calculation inline if x,y,z are all integers — which is the use case I need.

from xyzservices import TileProvider

class TMSTileProvider(TileProvider):
    def build_url(
        self,
        x: int | str | None = None,
        y: int | str | None = None,
        z: int | str | None = None,
        scale_factor: str | None = None,
        fill_subdomain: bool | None = True,
        **kwargs,
    ) -> str:
        if (type(x) == type(y) == type(z) == int):
            y =  2**z - y - 1
        return super().build_url( x , y, z, scale_factor, fill_subdomain, **kwargs)

That‘s it.

Note:
1. I am only a part time python programmer, not sure if it fits all coding rules.
2. I am not sure where this fix should go: contextily or xyzservices ?

Cheers