[GRASS-user] d.rast.arrows in GRASS6.4.2RC3 wxpython GUI

Aldo Clerici aldo.clerici at unipr.it
Mon Feb 13 05:06:23 EST 2012

GRASS users and developers.


In GRASS6.4.2RC3 with wxpython GUI the option 'Add raster cell arrows' seems
not to work properly. It seems that the arrows in the Map Display cannot
zoomed in..

It can be checked by the following steps:

Load and display the aspect (Spearfish) map.

Open the d.rast.arrows panel through the GUI button and choose the same map

Click Apply: the Map Display appears green as espected for the very high

Choose 10 for  the 'Draw arrow every Nth grid cell:' option and none as
'Color for drawing grid or "none"' option. The arrows are displayed on the
cells of aspect map.

To make the arrows visible choose slope as 'Raster map containing values
used for arrow length:' and 10.0 as 'Scale factor for arrows'.

Zoom in a very small area: the cells of aspect map are enlarged, but the
density of arrows remains the same  

The direction is correctly  the same for all arrows inside the same cell but
it seems that instead of having an arrow each 10 aspect cells, there is an
arrow each 10 pixel of the screen.

Something wrong in my procedure or is this a bug in wxpython GUI (with tcltk
GUI the procedure works fine)?


A. Clerici

Parma University


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