9 Replies Latest reply on Feb 14, 2020 9:44 AM by Greg Maya

    Spatial data (non) overlap with background image

    Greg Maya

      Hi all,


      This is an issue that I've had as a "blocker" for quite a few months and I've been unable to make any progress despite the various resources about background images for a map view (like this one).
      Maybe there's someone out here that is familiar with coordinate systems (and their transformations) that can give me a hand.


      The problem:

      I have POINT data originally in CRS 27700 (British National Grid) representing desks at an office layout. This is data that's stored in a PostGIS database and therefore its geometry type is WKT. In order to map it in Tableau I had to extract the individual X (longitude) and Y (latitude) points** after making a coordinate transformation. Like so :st_x(st_transform(geom,4326)) . - st_y(...) for latitude.

      The not so nice surprise comes when I try do insert my background image (which also comes from the same database but this time I've exported as raster file - as I just need there as a reference) and realise that they actually don't overlap as they originally did in QGIS (desired image attached).


      I cannot understand where the issue might be as I'm using the same transformation for my basemap to get the extents of the geometry (its bounding box) : st_extent(st_transform(geom,4326))



      Whoever, feels like something on the steps described above could be done better to achieve an appropriate overlap please fire up ! You'd unlock a whole new set of spatial filterings for me.


      Many thanks,




      ** (accepting WKT would be fab, but current versions don't support that data type)



      Desired :