Choosing an ellipsoid

[Adalberto da Silva]

Hello!

        I'm working with a database on a UTM projection in an area
located on
Southeastern Brazil.

        My primary map source is a set of 1:50,000 topographic sheets
that were
generated based on SAD69 datum.

        Well, I'm working in such a total area that can be well
considered as
flat as the Earth was several centuries before... But I want to make my
work suitable for insertion on larger datasets and projection issues
must become very important.

        Do I choose International ellipsoid? Are there any documentation
explaining the ellipsoid definitions used in Grass?

        Thanks,
-- 
Adalberto da Silva
Instituto Astronomico e Geofisico - USP
Sao Paulo - Brasil
adalbert at iag.usp.br