[GRASS-user] Display arrows on basis of vector points

GRASS GRASS user
1

Hi!
Does anybody know if it's possible to display arrows starting from vector points
which have a x_shift and y_shift attribute for their direction/length.

I would like to use it for displaying flow velocities of glaciers!

Bernhard Hoefle

2

On Tuesday 23 May 2006 09:03, Bernhard Reimar Hoefle wrote:

Hi!
Does anybody know if it's possible to display arrows starting from vector
points which have a x_shift and y_shift attribute for their
direction/length.

I would like to use it for displaying flow velocities of glaciers!

Bernhard Hoefle

_______________________________________________
grassuser mailing list
grassuser@grass.itc.it
http://grass.itc.it/mailman/listinfo/grassuser

Hi,

I am not sure if this is currently possible outside of a custom script
involving d.mapgraph -- but it is quite simple to do in R with the arrow()
function.

Search the CRAN website for examples.

Cheers,

--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341

3

Do you know about d.rast.arrow? It takes a grid of directions and a
optional grid of magnitudes and can generate vector fields. I use it
to plot wave and current fields.

David

On 5/23/06, Dylan Beaudette <dylan.beaudette@gmail.com> wrote:

On Tuesday 23 May 2006 09:03, Bernhard Reimar Hoefle wrote:
> Hi!
> Does anybody know if it's possible to display arrows starting from vector
> points which have a x_shift and y_shift attribute for their
> direction/length.
>
> I would like to use it for displaying flow velocities of glaciers!
>
> Bernhard Hoefle
>
> _______________________________________________
> grassuser mailing list
> grassuser@grass.itc.it
> http://grass.itc.it/mailman/listinfo/grassuser

Hi,

I am not sure if this is currently possible outside of a custom script
involving d.mapgraph -- but it is quite simple to do in R with the arrow()
function.

Search the CRAN website for examples.

Cheers,

--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341

_______________________________________________
grassuser mailing list
grassuser@grass.itc.it
http://grass.itc.it/mailman/listinfo/grassuser

--
David Finlayson

4

> > Does anybody know if it's possible to display arrows starting from
> > vector points which have a x_shift and y_shift attribute for their
> > direction/length.
> >
> > I would like to use it for displaying flow velocities of glaciers!

..

> I am not sure if this is currently possible outside of a custom
> script involving d.mapgraph -- but it is quite simple to do in R
> with the arrow() function.

FYI, d.mapgraph is depreciated in GRASS 6.1, use the much improved
"d.graph -m" instead. Maybe modify the arrow symbol (or make 8, 1 for
each dirn), with tail at 0,0. See display symbol help in the wiki
add-ons. Support for custom rotation is still not finished for symbols.

Do you know about d.rast.arrow? It takes a grid of directions and a
optional grid of magnitudes and can generate vector fields. I use it
to plot wave and current fields.

(again, GRASS 6.1-cvs version only)
screenshots:
http://bambi.otago.ac.nz/hamish/grass/d_rast_arrow_360.png
http://bambi.otago.ac.nz/hamish/grass/d_rast_arrow_360b.png
http://bambi.otago.ac.nz/hamish/grass/d_rast_arrow_magnitude.png

Hamish