[Gdal-dev] datum shift in OGR / proj4

[mathieu_gdal]

Dear All,

I know the basics of datums concepts, and until now, I was making datum
conversion with my own code (using in particular the abridged Molodensky
formula).

Now, I would like to port my code to OGR.
Where could I find documentations about how to convert datums with Proj4
/ OGR? 
In can see in this mailing list some experts talking about "Datum Data
files". I have my own datum list and file format, so is it possible to
feed Proj4/OGR with my own datums?

If you could give me a "starting point" (doc and/or code) to allow me to
start with OGR and datums, it would be great.

Mathieu