Many Thanks! Guessing would not have worked here...
david
On 06/27/2013 05:07 PM, Hamish wrote:
David wrote:
I would like to plot data which consist of a number of points, each of
which has a latitude, a longitude, an x-velocity, and a y-velocity. I
want to plot an arrow for each point that starts at the proper latitude
and longitude, and has a length and direction that show the velocity. I
used to think of these as vector values, but in GRASS a vector is
something else. What is the proper GRASS terminology for this kind of
data? What modules do this kind of plot?
Hi,
use the d.barb module from GRASS 6 addons.
http://grasswiki.osgeo.org/wiki/AddOns/GRASS_6#d.barb
x and y components of velocity are given using attribute column names
in the u= and v= parameters when a GRASS vector (i.e. sparse points)
input= map is given.
"vector maps" mean defined by coordinates, so points, lines, and areas.
"raster maps" mean defined by 2D or 3D array, so constant grids and pixels.
d.barb will work with both GRASS raster and vector points maps,
the meaning of the u=, v= parameters changes according to the context.
Usage:
d.barb [-r] [direction=name] [magnitude=name] [u=name] [v=name]
[input=name] [layer=value] [style=string] [color=name] [skip=value]
[scale=value] [peak=value] [aspect_type=string]
[legend_at=x,y[,x,y,...]] [legend_velo=value[,value,...]]
[legend_fontsize=value] [--verbose] [--quiet]
Flags:
-r Rotate direction 180 degrees
Useful for switching between atmospheric and oceanographic conventions
--v Verbose module output
--q Quiet module output
Parameters:
direction Raster map (or attribute column) containing velocity
direction
magnitude Raster map (or attribute column) containing velocity
magnitude
u Raster map (or attribute column) containing u-component of
velocity
v Raster map (or attribute column) containing v-component of
velocity
input Name of input vector map
layer Layer number
A single vector map can be connected to multiple database
tables. This number determines which table to use.
default: 1
style Style
options: arrow,barb,small_barb,straw
default: arrow
color Color
Either a standard color name or R:G:B triplet
default: black
skip Draw arrow every Nth grid cell
default: 10
scale Scale factor for arrow rendering
default: 1.0
peak Maximum value for scaling (overrides map's maximum)
aspect_type Direction map aspect type
options: cartesian,compass
default: cartesian
legend_at Screen percentage for legend barb ([0,0] is bottom-left)
Draws a single barb and exits
options: 0-100
default: 10.0,10.0
legend_velo Velocity for legend key arrow
legend_fontsize Font size used in legend
default: 14
it's still a work in progress, but ~90% of the features are working.
Hamish
_______________________________________________
grass-user mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/grass-user
