Not often I get requests….well, not often I get requests which lay down the guantlet. In my previous post “GIS Tips – Don’t trust your GIS, have you heard of OSTN02?” I am quite flippant when mention how to add the OSTN02 to the QGIS system, then I got a couple of replies to my blog pointing out that it really isn’t that easy….
I’m not one to run away way the going gets tough, so here goes….
Adding the OSTN02 transformation to QGIS
First download the OSTN02 transformation from the Ordnance Survey website: here
Then extract the files to a folder you will easily be able to find later. Essentially all you REALLY need is the OSTN02_NTv2.gsb file – The GSB format is also NTV2 format (I believe) and is a grid of binary transformations.
Okay, here is the tricky bit, please only attempt this if you are on QGIS 1.8 and above….
Navigate to C:\Program Files\Quantum GIS Lisboa\share\proj\
Copy the OSTN02 gsb file into this folder
Open QGIS and add the transformation tool add-in. Without this addi-in all this would be impossible!
Obviously set WGS84 and British National Grid as your 2 coordinate systems and away you go!!
I tested this (as you can see above) and it works great!! Some might say it is even easier than the ESRI install!!