Issue: Support for generating vector tiles in non-Web Mercator tile schemes (e.g., EPSG:4326 or EPSG:4490)

[vlv-squid]

Problem Description
I understand that Tippecanoe supports reading data sources in WGS84 (EPSG:4326) coordinate system and by default generates vector tiles using the Web Mercator (EPSG:3857) projection tile scheme. I would like to confirm if Tippecanoe itself can directly generate vector tiles using EPSG:4326 or EPSG:4490 tile schemes.

The key point here is that I'm not concerned about the coordinate system of the data source itself (I know the data source can be EPSG:4326), but rather whether the final tile output can use non-Web Mercator tile schemes.

Current Behavior vs. Expected Behavior
Current Behavior: Regardless of the input data's coordinate system, Tippecanoe outputs vector tiles using the Web Mercator (EPSG:3857) projection tile scheme.

Expected Behavior: Hope Tippecanoe can provide an option (such as a new command-line parameter) to support generating vector tiles in other coordinate system tile schemes, such as geographic coordinate system (EPSG:4326) or China Geodetic Coordinate System 2000 (EPSG:4490).

Attempted Alternatives
Since Tippecanoe currently doesn't seem to support direct output of non-Web Mercator tiles, I've explored some possible alternatives:

Tool Conversion: Attempted to use other tools (like GDAL) to convert tile data coordinates after generating standard Web Mercator tiles with Tippecanoe. However, this approach is very complex because both the tile scheme (such as XYZ vs. TMS tile indexing) and the coordinates within the tile data need to be converted, making it difficult to ensure correctness and efficiency.

Finding Alternative Tools: Also explored whether other vector tile tools natively support EPSG:4326 or EPSG:4490 tile schemes.

Additional Context
In certain specific application scenarios, particularly projects related to Chinese geographic information data, there's a need to use the China Geodetic Coordinate System 2000 (EPSG:4490). Additionally, some 3D globe applications often require tiles in geographic coordinates (EPSG:4326) directly to avoid client-side projection transformations.

I've noticed that in Tippecanoe's official documentation and existing issues, there's no clear statement or option about directly outputting non-Web Mercator tile schemes. Parameters like -s or --projection appear to be mainly used for specifying the input data's coordinate system, rather than controlling the output tile scheme.

If Tippecanoe currently cannot directly implement this feature, is the development team considering adding support for non-Web Mercator tile schemes in future versions? Alternatively, could you recommend any viable workarounds or alternative tools to help generate such tiles?

Thank you for your time and attention to this matter!

[e-n-f]

Can you say more about what renderers expect to find in non-mercator tiles? Internally, tippecanoe does not care very much about the projection of the output tiles, and just knows that it is generating tiles on a square cartesian plane in which (0,0) is at the top left. If you can point me to specific projects that expect EPSG:4490 or EPSG:4326 tiles, perhaps I will be able to understand their expectations. In EPSG:4326, for example, the world is not square: it is a rectangle that is wider than it is tall. Where does this rectangle sit within the square coordinate system of map tiles?

[vlv-squid]

Can you say more about what renderers expect to find in non-mercator tiles? Internally, tippecanoe does not care very much about the projection of the output tiles, and just knows that it is generating tiles on a square cartesian plane in which (0,0) is at the top left. If you can point me to specific projects that expect EPSG:4490 or EPSG:4326 tiles, perhaps I will be able to understand their expectations. In EPSG:4326, for example, the world is not square: it is a rectangle that is wider than it is tall. Where does this rectangle sit within the square coordinate system of map tiles?

Thanks for the response! Let me clarify our use case:

We are not asking Tippecanoe to embed CRS metadata in MVT (we know it doesn’t support that). Instead, we need support for non-Mercator tiling schemes, specifically EPSG:4490 (CGCS2000) or EPSG:4326 geographic coordinates with a plate carrée grid.

In China, national GIS standards require data to remain in EPSG:4490. Platforms like Tianditu (National Map) and SuperMap already serve vector tiles using a geographic tiling scheme where:

• The world is defined as [-180, -90, 180, 90] (degrees)
• Tile (z,x,y) corresponds to a longitude-latitude rectangle, not a Web Mercator square
• The MVT geometry is encoded in local pixel space [0,4096]^2, but the clipping envelope is in 4490

Frontends like OpenLayers or Cesium can render these tiles correctly if they use the same tiling scheme (via custom TileGrid).

So our request is: Add an option like --tiling-scheme=geographic that:

1. Uses geographic bounds for each (z,x,y)
2. Does NOT reproject input geometries (keeps them in 4490/4326)
3. Clips and encodes MVT directly in the original CRS

This is already possible in PostGIS with ST_AsMVTGeom(geom_4490, envelope_4490, ...), but Tippecanoe currently forces everything through Web Mercator.

Examples of real-world usage:

• Tianditu Vector Tile Service (China)
• SuperMap iServer (supports EPSG:4490 vector tiles)
• OpenLayers custom TileGrid for EPSG:4326

Would this be feasible?