[GRASS5] New NVIZ fly navigation

[Massimo Cuomo]

Hello everybody.

A new "immersive" navigation for NVIZ has been added by Markus to the 
CVS repository.

This "fly" navigation allows to move the 3D point of view with mouse 
buttons and movements. With the new basic 3D graphic cards that are now 
usual even on laptops, it can be useful to fly not only over, but 
"inside" the DTM 3D models at high resolution. The flythrough addition 
to NVIZ allows to do so in 3 different ways that are explained directly 
on the user interface. Furthermore, navigation can be quickly switched 
between "coarse" and "fine".

For developers: a callback mechanism has been added that allows to 
register external functions and calls them at the "appropriate" moments 
in the drawing loop, after everything else has been drawn.

We at ACS (an Italian software company) are using GRASS/NVIZ for a 
research project about the desertification named RIADE (www.riade.net) 
and have developed several functions: the flythrough is the most general 
purpose of them.

I have to thank my colleagues and especially the project manager that 
trusted and allowed us to use free software for this project.

Massimo Cuomo