GRASS GIS (Geographic Resources Analysis Support System) is a free, open source geographical information system (GIS) capable of handling raster, topological vector, image processing, and graphic data.

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4
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2answers
976 views

How do I split polygons into line segments?

How can I split my polygon file into "segements"? The lines should be broken up like this picture shows:
5
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5answers
1k views

How to generalize and vectorize a LandUseClassification raster file?

I want to vectorize that rasterfile with its 6 landuse classes. The classification is very noisy and have to be generalized before. The result should be a polygone vector file. I use SAGA, (GRASS) ...
1
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2answers
257 views

How to join polygons and lines vector maps from openstreetmap?

I am struggling with the data format OSM gives me: I want to use OSM data for routing, but all round-abouts and parking lots are not in the lines layer. They are situated in the poly(lines) layer. ...
5
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4answers
4k views

Dissolve ploygons in QGIS or Grass to new polygons of defined population sizes

I have a shapefile with 3800 polygons representing the smallest administrative areas in Ireland. Many of these, in rural areas, have tiny populations, under 100 people. In urban areas, all would have ...
3
votes
1answer
425 views

Where to change GRASS GIS wxGUI language?

I use GRASS 6.4.2 on Russian version of Windows 7 x64. As I start wxGUI it is shown in Russian. But I don't like its translation and want to work with English interface. I have no clues how to solve ...
4
votes
1answer
933 views

Quantum GIS Affine

I have a vector floorplan (DXF) that I've added to a blank project in QGIS using the Dxf2Shp plugin. I've been reading tutorials and StackExchange threads, but I can't seem to find out how to ...
7
votes
1answer
295 views

Can I use GRASS algorithms in Sextante under ArcGIS?

Sextante for ArcGIS comes with SAGA modules. I know that I can use GRASS algorithms in Sextante under gvSIG. But how can I use GRASS algorithms in Sextante under ArcGIS? I tried to look for any ...
3
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2answers
2k views

How to calculate LS Factor of Watershed for RUSLE Calculation?

I managed to get subbasins for my catchment (7 km^2) with their areas but I haven't figured out how to get the LS factor (see Revised Universal Soil Loss Equation) from it. I have the vector file ...
3
votes
1answer
530 views

r.watershed analysis error from raster map being in different zone and unable to be opened

I tried running my DEM (geotiff) file through the r.watershed program by the GRASS GIS plugin of QGIS. I believe the error message results from a raster map in the different zone than the current ...
2
votes
2answers
1k views

How to perform volume calculation in QGIS

EDIT 07/12/12 Ok, meanwhile I came to another problem I want to discuss. I just tried around with the volume calculation with some layers and came to a point where I receive the following error. ...
3
votes
3answers
488 views

Topographic correction (for land use classification) with SAGA or GRASS

Is there a module in GRASS or SAGA (or a alternative open program) to do a topographic correction of a landsat image to enhance the land use classification? Thanks! Martin
0
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1answer
703 views

Compiling Grass from Source in Ubuntu

Hi a while ago I drafted a semi-universal guide on how to compile GRASS GIS on Ubuntu. Because I had enough emails asking more details I thought to post it here for everyone and if possible to ...
1
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1answer
75 views

Is there a way to access ps.map in python?

i am wondering whether its possible using python interface to load layers and edit them in Print/Cartographic Composer without displaying, and finally export to PDF? something that can be done via ...
2
votes
2answers
380 views

count features in polygon shapefile A that fall within each feature of polygon shapefile B

I have two polygon shapefiles, each of which contain multiple (possibly overlapping) polygons. Is there some way, using GRASS, to calculate the number of polygons belonging to shapefile A that fall ...
1
vote
2answers
941 views

How to access vector coordinates in GRASS GIS from python?

Is there a way to iterate over lines and their vertices using python? I'm new to GRASS GIS, and it looks like there are ways to read raster (for numpy), but I don't see a direct way to access ...
3
votes
1answer
530 views

Correct ASTER with SRTM or Topographic Map

I have a problem with my DEM again. I decided to use ASTER GDEM2 (for different reasons). ASTER GDEM2 have its problems, I know, and I dont want to discuss that again. I have to use it, because SRTM ...
4
votes
1answer
1k views

How to create a Digital Elevation Model

How to create a DEM starting from layers shapefile "contour lines" and "shares"? which module of GRASS I need to use? thanks for yours responses....
0
votes
1answer
19 views

How do I add “padding” to features when applying d.out.file to map display on GRASS?

Thing is this. I've done up a script to automate some spatial interpolation and eventually output the interpolated raster and contour lines as an image of the map display. I'm doing this using ...
2
votes
1answer
360 views

How to overlay my interpolation within the boundaries of Quebec?

I am trying to create interpolated maps within geographical borders. I have the coordinates and values to the points I am trying to interpolate. I also have a map of the geographical land mass in ...
12
votes
2answers
993 views

Is it possible to manually correct a raster DEM (OpenSource)?

Is it possible, to correct a raster DEM by changeing the raster-cell-values manually, like by "painting"? My DEM (ASTER) have one small error where the elevation is about 300m below the actual ...
2
votes
2answers
173 views

River drain: r.watershed to vector is not working

I want to vertorize the result of r.watershed (accumulation). After using r.to.vect I got the message that I have to use r.thin before. So I did, but the message comes again and again. What I am ...
5
votes
1answer
2k views

How to do Kernel density analysis in QGIS 1.7?

Do someone have some suggestion? We would like to tray Kernel Density analysis as we did with ArcGis using QGIS?
2
votes
2answers
376 views

Error Importing dbf File Into GRASS

I am working on an assignment which requires me to connect to a database, then import a dbf file into the database using the command db.in.ogr (as can be seen below). However, GRASS simply won't ...
0
votes
1answer
177 views

error using GRASS v.proj

When I try to use v.proj to reproject my map from OSGB to GoogleMaps coord system I get this error.... Reprojecting primitives: pj_transform() failed: failed to load datum shift file ERROR: Error in ...
1
vote
1answer
447 views

Merge two maps with OR operation in GRASS

I have two vector maps. The two maps cover the same area but are split up into polygons differently (i.e. if you were to imagine one map placed above the other, the lines defining the polygons would ...
1
vote
1answer
196 views

v.dissolve renames the attribute table column and does not produce a dbf

When I run v.dissolve on my vector... v.dissolve --o input=pass2@mapset1 layer=1 column=fttcp output=pass3 The dissolving appears to work but the column name in the attribute table has changed from ...
4
votes
5answers
830 views

Elevation correction ASTER GDEM2 (+10m)

My ASTER GDEM2 has a average elevation error of -10m for my area. (I testet it using 90 defferential GPS reference points and compared it with old Topo25, SRTM, and GoogleMaps). I would like to ...
2
votes
1answer
434 views

Using nviz module in GRASS through qgis error

I'm an new user to qgis/GRASS and I've run into a problem with the nviz module. In trying to visualise a raster heat map created from vector contours in 3D using the nviz module in GRASS tools in ...
2
votes
2answers
1k views

How to vectorize a Raster-Classification? (qgis, grass)

I classified my raster-DHM into elevation levels using colormap. Its not a "real" classification, just a colormap. So I cant vectorize the classes to get polygones for every class. Whats the best ...
7
votes
5answers
3k views

Large mosaic process failing - what are the options? software independent only focussed on result

I need to mosaic about 550Gb of tif imagery together and the software I have tried keeps failing. The area has been split into zones so that the smallest has approx 200 tiles. I have used the latest ...
1
vote
2answers
749 views

Interpolation of contours (from one “main-contour-shapefile”)

I calculated, that the best and smalest possible äquidistance (equidistant) for my map is 30m. After I generlized my DHM, I extracted contours of a intervall of 30m and smoothed them. Now I have my ...
1
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1answer
202 views

hypsometric colors alà IMHOF, SYDOW or PEUCKNER

I need a hypsometric color-map to add it to my multishade-modell. (High Mountain between 800 and 4000m) There are a lot of differend typs explained in IMHOFS "Cartographic Relief Presentation". I want ...
4
votes
1answer
290 views

Multishading: bring them together to one Raster-Image

I made a multi-hillshade with 4 different light-directions and colors and stacked one above the other, each with its own transparency. Now I want to "save" the result in one raster-image. Whats the ...
2
votes
2answers
919 views

QGIS is not able to find GRASS. Choose the path of installation folder of GRASS

I've downloaded and then correctly installed QGIS 1.7.4 for windows (Win 7 64bit is my version) in C:\Programs\Quantum GIS. But everytime I start QGIS this popup appear: "QGIS is not able to find the ...
3
votes
1answer
631 views

Cell calculations; QGIS,GRASS,GDAL,SAGA

I recently asked a question about trying to calculate the slope over distance (manually) using QGIS, but then I came up with another way of solving the problem, but I would have to get some help for ...
1
vote
1answer
342 views

mdenoise/r.denoise: How to

I want to use mdenoise / r.denoise but i cant get it working. I have Xubuntu 12.04 and Grass 6.4.1 GRASS tells me after installing the plugin: g.extension extension=r.denoise ...
5
votes
4answers
802 views

How to automatically plot intermediate contours with QGIS, GRASS GIS or SAGA GIS?

I'm mapping a steep mountain range. My main contour interval is 50 m and my intermediate contour interval is 10 m. In steep areas, the interval of 10 m is too small, so I need to leave ...
15
votes
3answers
3k views

Visual Impact Assessment in QGIS or GRASS

Is it possible using QGIS or GRASS to perform a Zone of Visual Impact assessment? E.g. where can a 100m high structure be seen at a viewing height of 1.8m within 30km, taking into account elevation ...
3
votes
2answers
1k views

1'' DHM: Hillshade is too rough - how to “generalize”?

I got this hillshade from my DHM (I used the hillshade-module from qgis). For my purpose there is too much relief detail (roughness). How can I get rid of this in QGIS or GRASS? Thanks! Martin
1
vote
1answer
376 views

r.sim.water G_malloc error

I've been trying to run r.sim.water on a 3 meter LiDAR-generated DEM I have, but keep getting G_malloc errors: r.sim.water --verbose elevin=meterDEM.final@Sediment_Simulation ...
1
vote
2answers
241 views

Can GRASS read Spatialite geometry fields?

I've looked at the question: How to import SpatiaLite data into GRASS? already. The links there talk about two separate tasks: Passing SQL to a Spatialite DB from GRASS and connecting to Spatialite ...
1
vote
2answers
890 views

How to calculate the average value of a raster within polygons?

I am using the GRASS plugin in QGIS. I am trying to calculate the average value of a raster dataset within a set of polygons. I have created a new mapset and have imported both the vector and ...
1
vote
1answer
97 views

mapping number of days a site is flooded from daily inundated areas maps

I have a set of daily inundated area polygons and would like combine them into one map that can give me a map showing the number of days a site remained inundated. I am unable to figure out any ...
1
vote
1answer
304 views

Why can't r.patch find the rasters?

I have elevation rasters which loaded just fine in a GRASS session. They represent adjacent areas, so I want to meld them into one raster. I ran r.patch using the GRASS GUI, and it would only accept ...
0
votes
1answer
361 views

GRASS and QGIS- “ not recognized…format” but it worked before

Prologue: I used my Ubuntu file viewing GUI to move data files around and "clean house" a bit. I started a new GRASS session and tried to add NED elevation rasters which I have successfully added ...
0
votes
1answer
50 views

Does 'r.patch' act only on “loaded” rasters?

Can I run the GRASS command 'r.patch' on raster files which are not "loaded" into the current GRASS session? That is, rasters which are simply in my folder but not in a GRASS location & mapset? ...
0
votes
1answer
140 views

GRASS importing same-name rasters fails

I have NED elevation data in 3 rasters. (That's how it downloaded from USGS NED page.) The files are named "61471006", "61471006_2", and "61471006_3". I succeeded in using the GRASS GUI and menu ...
0
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0answers
131 views

Making a Bridge Classification tool in GRASS GIS

I'm working on a tool for classifying bridges with GRASS. I have been using examples online but I've come to a standstill as how to actually make this tool in GRASS. I have my raster of my area and ...
0
votes
1answer
206 views

How to specify column names with v.in.ascii

I have managed to import a CSV file into a points vector file using GRASS v.in.ascii v.in.ascii --o input=test1.csv output=test2 format=point fs=, skip=1 x=2 y=3 z=0 cat=0 This is test1.csv ... ...
2
votes
2answers
600 views

r.mapcalculator and python again

I've been trying to write a script creating binary maps: a=raw_input ("enter a threshold") b=float(a) grass.run_command('r.mapcalculator', formula="**'base_map'>=b**", outfile='map'+str(a), ...