I'm trying to get some OSM data to overlay correctly over Lidar data. The OSM data according to their wiki is WGS84. The lidar is [EPSG:27700][1]. So as you can imagine they don't line up/overlay properly as there is a relative warping effect going off.

If I could just acquire the conversion equation to convert WGS84 to EPSG:27700 I can write a small C++ file to parse the OSM files and convert all the lat and lon values.

Anyone know what the conversion calculation is?

I explored vector reprojection of the Osm data in QGIS, and Reprojecting the OSM wgs84 data to epsg 27700. The match the the Lidar is close enough for what I need. Unfortunately it isn't possible to save the change back to the Osm which contains other data I want to retain alongside. If I've understood some the information on this correctly, QGIS uses Proj4 for the reprojection calculations. Attempting to decipher the C++ code to extract the exact calculation used is proving tricky due to the sparse pseudocode comments within it.

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    "Overlay correctly" in what software? – TomazicM Apr 29 '19 at 11:55
  • Have you had a look at the description of the EPSG-codes/projections? – Erik Apr 29 '19 at 11:55
  • Most of the information you require can be found in https://www.ordnancesurvey.co.uk/docs/support/guide-coordinate-systems-great-britain.pdf. Note for greatest accuracy you should use the OSTN15 transformation. – JimT Apr 29 '19 at 12:25
  • Almost any GIS will be able to do this – Ian Turton Apr 29 '19 at 13:41
  • Thanks for the responses, I can see from looking at your link JimT that this question would fall into Myth 4. I am a GIS noob and I just assumed that conversion would be a case of applying some specific maths equation to the problem, and out pop my nice new curve free Osm data. Erik, I haven't looked at that, this kind of thing is very alien to me, but I will have a read and try to understand. TomazicM, within 3d modelling software. I have two layers, one is a DSM, the other is an Osm data. Over a 4km stretch, the curve on the Osm is apparent so it doesn't match the lidar data. – James Apr 29 '19 at 13:49

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