Give #LiDAR files a coordinate system with no GIS

I am not perfect, my wife will tell you that in abundance and yesterday I realised just how rubbish I am….I was sent a LiDAR capture of some woods and no matter what I did, it wouldn’t render in the right place. I knew the cloud was captured in EPSG 27700 (British National Grid) using the EGM96 geoid but there didn’t seem to be a projection file (.prj).

So here is a little trick which I discovered about 15 years ago when working with unreferenced raster data (which were supposedly referenced). For this you will need;

  1. An unreferenced .las or .laz data for which you know the coordinate system
  2. A shapefile which is in the coordinate system that the LiDAR should be in
  3. (Optional) A little energon and a lot of luck

Here we go:

Here s the “walk” data to be referenced

Take your shapefile and copy the .prj file and paste it into the folder with the LiDAR data

Here is my “Bournemouth” shapefile which I know is in EPSG 27700

 

File is copied to the folder

Rename the .prj file to that of your LiDAR data, in this case, to “WALK LiDAR Data.prj”

Projection file renamed, this is case sensitive

That’s it!! You’ll find it now works!

But why does it work?

When there is no projection defined within the point cloud, most GIS look to supporting files to check for references. In this case the .prj file only defines the EPSG information in a GIS readable format, in this instance it just tells the GIS that the coordinate system is BNG, see here (you can open the .prj in notepad or other text reader)

*hint* most GIS files open in notepad

Once the GIS has a reference for the file, it can project the data to the correct location, which in this case is Sherwood forest, Nottinghamshire, UK.

….and no GIS was used at any point!!

Special thanks to 3D LaserMapping (3DLM) for the use of their LiDAR data

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