How to support a custom coordinate system?

[bayberryan]

I added a custom CRS to the spatial_ref_sys table in PostgreSQL and assigned it an SRID of 900105.When importing the SHP file, I set the SRID to 900105. The imported table can be loaded normally in QGIS, and after converting it back to SHP, it can also be loaded correctly in ArcMap. However, the tiles obtained through TIPG are all blank.

• custom crs

• in tipg

• in arcmap

[AndrewAnnex]

@bayberryan I also deal with lots of custom projections in my work (not yet with tipg... but I came across this issue while considering to use it) and my suspicion is that it has to do with the calls to to_epsg(), or in other places where epsg:4326 are assumed.

@vincentsarago I was about to open another issue but think this one will suffice, I was talking with Chuck Daniels fairly recently so I'll send him an email to forward to you for work I am doing that would benefit from this.

[vincentsarago]

I think the problem is that we're using proj (pyproj) for some operations (outside the database). You might need to also register your custom projection

tipg/tipg/collections.py

Lines 597 to 631 in b325f00

	if tile and tms and geometry_column:
	# Get tile bounds in the TMS coordinate system
	bbox = tms.xy_bounds(tile)
	left, bottom, right, top = bbox
	# If the geometry column’s SRID does not match the TMS CRS, transform the bounds:
	# Use a fallback of 4326 if tms.crs.to_epsg() returns a falsey value.
	tms_epsg = tms.crs.to_epsg() or 4326
	if geometry_column.srid != tms_epsg:
	transformer = TransformerFromCRS(
	tms_epsg, geometry_column.srid, always_xy=True
	)
	left, bottom, right, top = transformer.transform_bounds(
	left, bottom, right, top
	)
	wheres.append(
	logic.Func(
	"ST_Intersects",
	logic.Func(
	"ST_Segmentize",
	logic.Func(
	"ST_MakeEnvelope",
	left,
	bottom,
	right,
	top,
	geometry_column.srid,
	),
	right - left,
	),
	logic.V(geometry_column.name),
	)
	)

☝️ here we need to be able to transform the tile bbox to the table CRS (in your case it's your custom crs)

I'm no expert in Postgis but it would be nice if you could share the steps to register a custom CRS and some of your data, so we can write a tests and maybe a fix in tipg 🙏