[GRASS5] r3.out.vtk vector data export

[Sören Gebbert]

Dear all,
i have added vector data export to r3.out.vtk. 
If you have voxel data with vector informations, for example
three g3d maps with streamvector components x,y and z, you can
combine them with r3.out.vtk and visualize with Paraview.

I have added an example to the r3.out.vtk description.
Here are two screenshots of the resulting Paraview visualisation:

The vector data visualized with the Glyph Filter of Paraview
http://www-pool.math.tu-berlin.de/~soeren/grass/modules/screenshots/r3.out.vtk-vector-paraview1.png

Streamlines created with the StreamTrace Filter of Paraview
http://www-pool.math.tu-berlin.de/~soeren/grass/modules/screenshots/r3.out.vtk-vector-paraview2.png

Enjoy.

Best regards
Soeren