Which exact Geodetic system does Cesium use? Reprojecting BNG in Autocad 3D Map

Cesium for Unreal
1

Hello,

We are building a digital representation of a city in the UK, before Cesium came along everything was a bit simpler. We used the British Ordnance Survey maps (from digimaps) which are based on the BNG (British National Grid), these maps are great because they feature the location and layout of pavements (sidewalks), pedestrian crossings, paths, buildings (and their height), bus shelters as well as many other smaller details, in .dwg format, that are not present on OSM maps. This we can bring into a 3D software to model a 3D and textured version and then export into Unreal where it fits with the surroundings also from Ordnance Survey.

However since bringing Cesium on board to fill out the surrounding buildings and landscape with googlemaps photorealistic tilesets, we have encountered misalignment while matching up the work we have previously done and the 3D tileset. I have tried reprojecting our ordnance survey maps in Autocad map3D from BNG OSGB 1936 to WGS84 “WORLD-MERCATOR” however this still has some misalignment issues. I know reprojecting our maps won’t make it perfectly align with the tilesets but I would like it to at least align with the bingmaps buildings which use OSM

THE ANSWER IS
EPSG:4978

2

Hi @dardonal, welcome to the community!

I have a few questions so that we can get on the same page:

  • Are you able to share screenshots of the misalignment? These would be most helpful!
  • If the answer to the above is no, is this misalignment with respect to terrain height? Or does this misalignment also happen across the surface?
  • Does this misalignment also happen with Cesium World Terrain and OSM Buildings? Or is it only with Google Photorealistic 3D Tiles?

Thanks!

1 Like
3

Hi Janine,

I think I have worked out my problem. Here it says that Google Earth and OSM data use EPSG 4326 which uses degrees as units, so when I reproject my BNG maps to WGS84 the scale is wildly off. Is this correct?