2

Web Mercator projection is not a good match for polar region, and I need to use "Sphere Azimuthal Equidistant" for a project: https://epsg.io/53032

I'm able to add the projection to PostGIS/Carto by running this query:

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 53032, 'ESRI', 53032, '+proj=aeqd +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +a=6371000 +b=6371000 +units=m +no_defs ', 'PROJCS["Sphere_Azimuthal_Equidistant",GEOGCS["GCS_Sphere",DATUM["Not_specified_based_on_Authalic_Sphere",SPHEROID["Sphere",6371000,0]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Azimuthal_Equidistant"],PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",0],PARAMETER["Latitude_Of_Origin",0],UNIT["Meter",1],AUTHORITY["EPSG","53032"]]');

This gives me this top level tile (0/0/0) from Carto:

enter image description here

I need to match this tile with another service (WMTS), where I need to specify the extent and resolution. Is there somehow I can get this information from Carto? How is the top level tile defined?

About projections in Carto: https://carto.com/blog/free-your-maps-web-mercator/

3

Even though you've set your backend project to something fun and polar, every other part of the Carto infrastructure is still assuming you're working in web mercator. That includes the tiler. So, what are the extents of tile zero in web mercator? If it's a whole-world tile at zoom zero (check) then it's

(-20037508 -20037508), (20037508 20037508)

And you can use those same extents in your polar projection to work out the extents of tiles in your custom pyramid.

  • Incidentally, I love that projection! Both north and south pole on the same map, relatively undistorted. Cool! – Paul Ramsey Sep 28 '16 at 17:51
  • After solving an issue with ellipsoid shift the tiles now match perfectly: osgeo-org.atlassian.net/browse/GEOS-7778 – Bjørn Sandvik Oct 2 '16 at 9:25
  • @BjørnSandvik Welcome to GIS SE. Even though you've been a member for a while, I notice you haven't taken the tour. If this has answered your question, please consider marking as the answer. See What should I do when someone answers my question?. – Midavalo Oct 2 '16 at 23:57
  • @BjørnSandvik If you have solved this yourself please consider posting your solution as an answer, which will then be available for other users – Midavalo Oct 2 '16 at 23:58

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