How to plot and make UTM WGS-84 map

[Joaquim]

@henri25

So if I want now to plot in zone 32T, I just have to write gmt mapproject -Ju32T/1:1 ?

Yes, see. A bit terse but yes.

@henri25

However, I have been taught when I was student to only use UTM (WGS84) with my gps device with

?
GPS measure their coordinates in the ECEF (Earth Centered Earth Fixed) reference. That is with respect to Earth center of mass. That is natural since satellites orbit around that point.
With the help of a ellipsoid (part of the WSG84 system) and a Geoid one can get the z coordinate but lon,lat are obtained by geometry. UTM (and all other cartographic) projection is just that, a projection and as such it implies deformations. So, no, UTM is not the best referencing system when working with GPS data. But it can be good enough.

@henri25

If now I want to make a map with UTM coordinate including the two zones 31T and 32T instead of lat° and long°. Is it possible with GMT ?

No, you can’t. Neither in GMT nor in any other software. Each zone (or graticule as is your case) is a different referencing system.

@henri25

How would you do it ?

You have to convert your points into a common referencing system. Lon,lat, Transverse Mercator, Lambert (which the French like very much), etc… and then plot them.