[GRASS-user] Questions about datum management

[Nikos Alexandris]

Hi Corrado,

On Fri, 2008-10-24 at 17:11 +0100, Corrado wrote:
> Dear friends,
> 
> a few questions on some things I do not understand well about datum:
> 
> 1) what is a datum tranformation parameter?

You might find the following pages interesting:
http://en.wikipedia.org/wiki/Datum_(geodesy) (under
http://en.wikipedia.org/wiki/Geographic_information_system)

and http://grass.osgeo.org/wiki/GIS_Concepts

[...]

> 3) why does the system ask for a datum transformation parameter when I create 
> a location with EPSG code 27700? The code should be enough to create 
> everything!

Be carefull with the codes. Not all epsg codes correspond to one
projection system. Some refer for example to the ellipsoid, others to
the units and more.

Maybe this document explains all!
http://www.epsg.org/guides/docs/G7-1.pdf

> 
> Regards

Kind regards, Nikos