Re: [GRASS-user] how to make a grid with my DEM
Janet wrote: Hi all,i want to simply divide my DEM into 30m grid cells - does anyone know how to do this? have a look at the r.resamp.stats module. a more complicated way is with v.mkgrid and v.rast.stats. Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] how to make a grid with my DEM
Hi Janet, Do you mean you want to create contour lines at 30m intervals? If so, r.contour would do the trick. Best, Nick On Sat, Feb 11, 2012 at 1:56 AM, Janet Choate jsc@gmail.com wrote: Hi all, i want to simply divide my DEM into 30m grid cells - does anyone know how to do this? i have previously used r.clump on a 30m DEM to create unique spatial units. however, since r.clump finds all areas of contiguous cell category values and groups them to form physically discrete areas, i end up with some spatial areas that may be larger than 30m. any help is very much appreciated! thank you, Janet ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] How to link or combine adjacent vector lines
On Sat, Feb 11, 2012 at 7:49 PM, Stefan Luedtke slued...@gfz-potsdam.de wrote: Sorry for the delay... and thanks for the fast answer. Adding a column and then running a command in the sense of v.dissolve is not an option because there are just to many. I was thinking of a way that combines two lines into one if they share the same node. For the example mentioned the last time, this means, keeping the line as a single one until the tributary merges the main river. The main river might consist of more than one line, but a short tributary should not. Maybe v.build.polylines is what you are looking for. If there are attributes associated with the lines, the cats option should probably be set to first or multi. HTH, Markus M I hope I dont miss anything obvious ;-) Cheers, Stefan On Fri, 2012-02-10 at 17:04 +0200, Micha Silver wrote: On 02/09/2012 11:59 PM, sluedtke wrote: Dear friends, I have been trying for some hours now but could not find any solution. We do have a shape file of a river network, but a bad one because single rivers consist of multiple lines. Just think of the easiest example, a river with one tributary. I would like to end up with an vector dataset that holds 2 lines for this example, one for the river and one for the tributary of course. In my case, the dataset holds, just as an example, 10 lines, and a distinct set of them makes either the river or the tributary. The lines of each set are connected by the nodes of the single lines. Any ideas how to get ride of this format are very welcome. You might be interested in this thread from a year ago. http://osgeo-org.1560.n6.nabble.com/snap-point-to-line-break-line-at-given-points-tp3887413p3887413.html The short story is that GRASS builds topology when importing a line vector. So each intersection of two lines (i.e. a tributary that branches off the main channel) will be made into a separate line. You can force GRASS to ignore topology, but you probably don't want to. And a correct river network does indeed keep each stream reach as a separate line. (Then you can use the various river network modules r.stream.*). So maybe your original shapefile is not bad... What you can do it add an additional column to the vector attrib table and indicate, in that column, which tributary each segment belongs to. THen you can select, display, label, calculate, etc based on this tributary attribute column. Would that help? Thanks in advance, Stefan -- View this message in context: http://osgeo-org.1560.n6.nabble.com/How-to-link-or-combine-adjacent-vector-lines-tp4381557p4381557.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Micha Silver GIS Consultant, Arava Development Co. http://www.surfaces.co.il ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] How to link or combine adjacent vector lines
Thanks for the detailed answer, but, my problem is much more trivial. I attached a screenshot to make myself more clear. /* The numbers refer to the categories of each line segment */ the tributary with cat 69 is fine, but the man channel consists of multiple lines, and, in fact, a lot of tributaries look similar. As I mentioned before, adding an additional column (to run kind of v.dissolve) is not really feasible because I have around 600 cat values. The task would be, to tell GRASS, to combine all lines of the main channel, for this example. But I think that is quite ambitious- like Micha wrote in his post. On Sat, 2012-02-11 at 15:19 -0800, Hamish wrote sluedtke wrote: I have been trying for some hours now but could not find any solution. We do have a shape file of a river network, but a bad one because single rivers consist of multiple lines. Just think of the easiest example, a river with one tributary. I would like to end up with an vector dataset that holds 2 lines for this example, one for the river and one for the tributary of course. In my case, the dataset holds, just as an example, 10 lines, and a distinct set of them makes either the river or the tributary. The lines of each set are connected by the nodes of the single lines. so you have a vector line map of a braided river (be it a real one or the product of a computer surface water flow program which creates artifacts) and you wish to generalize it into an idealized schematic vector network. An interesting challenge. I think the first step is to run v.buffer with a buffer distance greater than half the maximum width of the parallel braids. The next step is the reduction back to a center line, like r.thin but for vector areas. Often you could do v.to.rast - r.thin - r.to.vect, but that doesn't work well for rivers as they are usually long and thin: in order to fit the entire length of the river into the raster array you need to make the cell res very coarse compared to the width of the river. so it becomes the classic river mile / river centerline problem, and if you have a good solution to that (especially for cases when there are shoals and islands in the middle of the river and you don't have full riverbed bathymetry to find the thalweg) I'd be very interested to hear about it. the best I ever managed was v.to.rast at very high cell resolution then r.cost to find distance from the riverbank, then r.param.scale feature map to extract the ridgelines, then r.thin, and r.to.vect. (instead of r.param.scale you could also use r.slope.aspect and look for places where the slope of the cost-to-shore map is less than some small threshold) another idea is to make the crappy lo-res river centerline with r.thin, then use v.lrs or v.transects(addons) to make step points, then run a moving window along the river buffer area at high raster res, using one of the g.region temporary zoom addon modules (g.region.point is one). Then patch all the new vector segments together and run v.generalize to smooth the result. I'm pretty confident that would work reasonably well, but it wouldn't be very efficient. It would be much more efficient to have a geometric solution than one that needs rasterization, maybe something like filling the vector buffer area with lots of little circles of varying sizes, merging as many of them as possible, then extracting the center coord of each surviving big circle. as I said earlier, it's an interesting problem.. Hamish attachment: river_network_subset.png___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] How to link or combine adjacent vector lines
Stefan wrote: Thanks for the detailed answer, but, my problem is much more trivial. I attached a screenshot to make myself more clear. /* The numbers refer to the categories of each line segment */ the tributary with cat 69 is fine, but the man channel consists of multiple lines, and, in fact, a lot of tributaries look similar. ... The task would be, to tell GRASS, to combine all lines of the main channel, for this example. ok. do they overlap or join end-to-end? if they join, try Markus M's suggestion of v.build.polylines. if they overlap, try 'v.clean tool=rmdupl' Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] two questions: snap and close lines
Sample location here: http://int.faunalia.it/~paolo/test.tar.gz Confirmed by other users. Thanks. Il 27/01/2012 18:53, Markus Metz ha scritto: The only two options I can think of is giving v.edit a try, otherwise hand-editing. Urgh! Too bad, thanks anyway. Why does breaking not work? Maybe you need remove duplicates and clean small angles at nodes. You could try v.clean input=patched@paolo type=line tool=snap,break,rmdupl,rmsa thresh=1,0,0,0 output=patched_1 I'm not quite sure break do not work: new nodes are there, but in subsequent steps they are not treated as closed polygons. Thanks. -- Paolo Cavallini - Faunalia www.faunalia.eu Full contact details at www.faunalia.eu/pc ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] error in example
On Fri, Feb 10, 2012 at 7:23 PM, Paolo Cavallini cavall...@faunalia.it wrote: Hi all. I'm following the examples in: http://casoilresource.lawr.ucdavis.edu/drupal/node/438 but I get an error in: new_data - SpatialGridDataFrame(grd, data=data.frame(k=rep(1,G$cols*G$rows)), proj4string=CRS(x@proj4string@projargs)) Error in validityMethod(object) : unequal number of objects in full grid and data slot Any hint? Thanks a lot. BTW: the link to sample data should be changed to http://mirrors.ibiblio.org/grass/sampledata/spearfish_grass60data-0.3.tar.gz Perhaps Dylan (author, in CC) has an idea? Markus ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] How to link or combine adjacent vector lines
That did the trick, almost. They join each other -so v.build polylines ... worked, but, the table is exactly the same as it was before. The command output said, that the number of lines was reduced to almost 50%. Furthermore, if I check the cat number next to the lines (via d.vect) it looks fine for both methods, first and multi. But the table does not show any diffs and holds the same number of entries like the original one. I could not find anything about that in the manual. Anyway, thanks for hints, that helped a lot. Stefan On Sun, 2012-02-12 at 10:56 -0800, Hamish wrote: Stefan wrote: Thanks for the detailed answer, but, my problem is much more trivial. I attached a screenshot to make myself more clear. /* The numbers refer to the categories of each line segment */ the tributary with cat 69 is fine, but the man channel consists of multiple lines, and, in fact, a lot of tributaries look similar. ... The task would be, to tell GRASS, to combine all lines of the main channel, for this example. ok. do they overlap or join end-to-end? if they join, try Markus M's suggestion of v.build.polylines. if they overlap, try 'v.clean tool=rmdupl' Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Loosing color table when reprojecting raster file
Hi folks, I was preparing a some maps for a presentation and ran into a snag. I am trying to reproject raster maps from a Lat/Long to Irish national grid. I've done this before. This time I found that I had no color. I am using William Kyngesburye's GRASS 6.4.1-5. I also tried Michael Bartons GRASS 7 SVN. There are tiles already in the Project location that I reprojected before. They still have their color. It's just that these latest attempts seemed be be stripped of their color and I can just use r.color to put it back. That doesn't seem to work either. Any ideas as to what the problem might be? Kurt D. Springs ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Re: How to rescale an aspect map
I need the most suitable areas (with SE aspect) to have the value of 255 and the unsuitable (North aspect) to have the value of 0. Grass returns N=90 and SE=315 and flat=0. So the minimum value of aspect raster is flat areas and the max is areas with 359 degrees of east. I should set North as the minimum value and SE as the max value (most suitable areas). I should rescale the raster because I need to include it in an AHP method. All rasters will be rescaled in a common 0-255 scale. -- View this message in context: http://osgeo-org.1560.n6.nabble.com/How-to-rescale-an-aspect-map-tp4377272p4464174.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
