Hello all, I'm a newbie to GIS and especially GRASS, but I'm trying to create walking distance isolines (isospace?) from OpenStreetMap data, and so far I've been successful using PostGIS, pgRouting (driving_distance() function), QGIS, and the QGIS contour plugin. However I'd like to be able to do this via the command line for a web service, and would like to try and do this in GRASS, however I have had some difficulties.
Here is what I've created in QGIS and want to create in GRASS (the blue areas): http://wiki.openstreetmap.org/wiki/File:SRTS_walkability_before_new_sidewalk.jpg This is the Shapefile of points resulting from pgRouting's driving_distance() function, with the cost column containing the distance in km from the entrance to a school: http://dl.dropbox.com/u/23634456/terra_centre_1mile_points.zip I'm not sure what the best (and more importantly, fastest) method is to produce this, but here's what I have so far. I only care about creating filled areas for 1/4, 1/2, 3/4 and 1 mile (0.4, 0.8, 1.2, 1.6 km), so don't really need or want full interpolation (e.g. a gradient), especially if it takes more processing time. # read in shapefile to costs layer in terra_centre mapset v.in.ogr dsn=/home/user/points.shp output=costs@terra_centre # set bounds to match costs layer, and set resolution (for rasters) g.region vect=costs@terra_centre rows=256 cols=256 # idw interpolation doesn't seem to work well #v.surf.idw --overwrite input=costs@terra_centre output=interp_idw column=cost # perform interpolation of costs layer using cost column, and output to interp_rst layer v.surf.rst input=costs@terra_centre elev=interp_rst zcolumn=cost # set colors to be four solid shades of blue r.colors map=interp_rst@terra_centre color=rules 0 0:0:255 0.4 0:0:255 0.401 50:50:255 0.8 50:50:255 0.801 100:100:255 1.2 100:100:255 1.201 150:150:255 1.6 150:150:255 1.601 white 10 white end # create contour lines at 1/4, 1/2, 3/4, and 1 mile r.contour --overwrite input=interp_rst@terra_centre output=contour@terra_centre levels=0.4,0.8,1.2,1.6 My questions are: 1) Is there a better way to achieve what the contour plugin of QGIS does? 2) How could I create a polygon layer (for the four bands) from the contour layer? 3) How could I create a similar result using v.net.iso instead of pgRouting? Thanks for any help, -Josh _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
