Re: [GRASS-user] How to plot a vector field?
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 grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] How to plot a vector field?
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 grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] How to plot a vector field?
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? tia, david adam ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
