On Thu, Jun 13, 2013 at 9:25 PM, Luís de Sousa <[log in to unmask]>wrote:

> Dear Norman,
>
> Calculating the area of an ellipsoid segment is something you probably
> don't want to do. Most GIS software does not implement it, those that do
> use approximations. You can get an idea of the complexity here:
>
> http://www.math.auckland.ac.nz/Research/Reports/Series/539.pdf
>
> You should do as Mark says, first project that geodetic data using an
> equal area projection and then feed it to GeoMason. This way you can use
> GeoMason as a GIS.
>
>
I've also found that, for whatever reason, a lot of data has attributes
with those calculations already done for you.  I don't know why this may
be, but it doesn't hurt to check the attribute tables for your data to see
if that is the case.