[Proj] OSGB36

[John Smart]

> As a start, where can one get the grid shift values? Is there only one
> standard set?
>
Try http://www.gps.gov.uk/additionalinfo/questDeveloper.asp


> Isn't there any Linux library that will do this (commercial is fine,
> too)?

No idea, but it's a fairly trivial bilinear interpolation with a simple text 
file. They include very detailed documentation on the algorithm for forward 
and reverse calculations.

Good luck.