The QGIS transformation appears to be named as EPSG:1314. https://epsg.io/1314 so I thought I could transform the data with that to 4326, before sending to the 3DTiles writer. However, I can't find epsg:1314 as a transformation in the csMapReprojector in FME, and none of the available OSGB_to_WGS84 transforms give any better results. So do I need to recreate the transformation parameters of 1314 myself? Or is there another approach. I find it surprising that FME does not have this transformation already so I am starting to wonder if I am either missing something obvious or my approach is flawed.
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Datum transformation differences QGIS and FME osgb to wgs84
Hi all,
I've done some data preparation of OpenStreetMap data (epsg:4326) in QGIS and as part of that work reprojected the OSM data to epsg:27700, naughtily relying on QGIS on the fly reprojection without too much thought. That defaults to a transformation that looks good in QGIS for my purposes and aligns well with the OSM web tiles in QGIS. I now want to use the 3DTiles in FME visualisation to export the data as a Cesium web map (thus going back from epsg 27700 to 4326) but I see a shift of about 1m or 2m of my OSM data when in Cesium (i.e. the product of the FME writer). I presume this is because FME is doing a different transformation to go back (appears to default to using OSTN15 grid shift) to that which I applied in QGIS.
Best answer by daveatsafe
Hi @maptopixel,
I'm sorry, but this transformation is not shipped with FME, since most users want the more accurate grid transformation.
I have created a couple of definitions for you:
OSGB1936_to_WGS84_7Param - uses 7 parameter algorithm
OSGB1936_to_WGS84_Bursa - use Bursa Wolf 7 parameter approximation
I'm not sure which algorithm QGIS uses for the transformation, so I provided both. One of them should match the QGIS transformation.
Please copy the attached file into your Documents\\FME\\CoordinateSystems folder to make the transformations available to FME.
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