Setting coordinate system in CARTO Builder map?

Question

I uploaded a polygon layer in EPSG 25830, called 'parcels'.

I know that the geometries are reprojected and the dataset has two geometry columns:

• 'the_geom' in EPSG 4326
• 'the_geom_webmercator' in EPSG 3857.

To reproject the layer I added it to a map, which only has that layer. I used CARTO ‘Builder’. In the SQL option of the layer, I executed the following sentence, according to the documentation:

SELECT 
  ST_Transform(the_geom_webmercator, 25830) as the_geom_webmercator, 
  cartodb_id, 
  the_geom, 
  area
FROM 
  parcels

The SQL sentence runs, but the polygons disappear out of the map, despite I pressed the button ‘Center map on layer’, and played with the zoom. The data of the table continues appearing.

I also changed the base layer to a ‘color’ type, and also a personalized WMS. The layer polygons do not appear. When I reset the layer data to SELECT * FROM parcels the polygons appears over the personalized WMS basemap.

I also wanted to know how to request personalized WMS base maps in EPSG 25830, or any other SRC, if it is possible?

Answer 1

CARTO BUILDER only supports officially webmercator, everything from basemaps to bounding box computations are designed to work on that projection. If you want to render data from a CARTO account in another projection you need to develop an external application using CARTO.js.

If you remove the basemap it may be possible to render the data as you can see explained on this blog post, but I'm not sure if that would work (probably not) with UTM coordinates which are out of the coordinate range of the webmercator projection, compared to other projections like Robinson, or Albers.