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.

learn more… | top users | synonyms

6
votes
1answer
374 views

How to increase mask buffer and then offset it using r.mapcalc in GRASS?

I'm in the process of learning on how to remove clouds and cloud-shadows from Landsat images using GRASS. So far I was able to remove a lot of clouds from those images using i.landsat.acca, but it ...
1
vote
1answer
348 views

Is it possible to have self intersecting polygons in GML or shapefile?

GIS vector data for example GML or shapefile contains polygonal data. Lets assume, we have polygon A which has self-intersection which means that the edges in this polygon intersect with each other. ...
9
votes
4answers
4k views

Tutorial on how to model flooding using data from gauging stations along rivers in QGIS?

Can someone please direct me to a tutorial where I can learn more about how to model flooding using data from gauging stations along rivers using QGIS?
2
votes
2answers
454 views

How to single out country data from a world data map?

Say that i have two "data sources"; A global map of average wind speeds, A shape file (or similar information) of all country borders in the world. How do i combine these two sources and extract ...
1
vote
2answers
347 views

Network distance computations using GRASS

I'm an ArcGIS user who's interested in learning to use GRASS. Can anyone point out resources that will help me in learning how to obtain network distances between (1) residential locations (points) ...
1
vote
1answer
76 views

Hydrograph in GRASS

How to make hydrograph for a basin in GRASS? While surfing the GRASS home page, I came to know that some time back in GRASS 4.x a command r.water.fee exist. I understand, it is missing in GRASS 6.4. ...
6
votes
2answers
522 views

Why don't GRASS tools work in SEXTANTE? (QGIS, MacOS)

I've got both SEXTANTE and GRASS installed on my platform. GRASS-SEXTANTE report an error when I'm trying to create the Modeller, however, other tools (R) work fine in SEXTANTE. Do these tools have ...
1
vote
1answer
53 views

Watershed other than stream ( between two points)

Is there any method available to demarcate watershed for a location other than stream? I mean, if I want to find out the watershed for a place, where no stream available but, sheet of water can flow ...
1
vote
2answers
176 views

How to apply v.transform on a set of vector layers (GRASS 6.4)?

I have 64 vector layers, all of them must be warped using the v.transform module; the pointsfile is the same for all vectors. How can I apply the transformation recursively to all layers? I'm not ...
2
votes
2answers
93 views

How to rasterize vector data correctly in GRASS GIS 6.4.0?

I try to rasterize some vector data in GRASS GIS 6.4.0. Unfortunately, it always just works with one layer. Afterwards, there are just lines generated instead of rectangles. What am I doing wrong?
2
votes
0answers
470 views

GRASS GIS - r.water.outlet - What is my mistake?

I'm new to GIS - more so in GRASS GIS. I installed GRASS GIS 6.4.3svn in my Windows 7 machine. No problem in installation. Downloaded SRTM-Geotiff file Location, Mapset all o.k Used r.in.gdal to ...
0
votes
1answer
2k views

How to convert a regular point grid to raster? [duplicate]

Possible Duplicate: How to convert a point grid to a raster? I´d like to convert a regular grid (25 meter) of points (XYZ) to a raster. I have tried the GRASS-tool r.in.xyz but I always get ...
2
votes
1answer
555 views

How to join two polygon layers into a resulting layer with overlapping polygons merged together (including attributes)

I am trying to find a method (in QGIS and/or GRASS) to join two layers of polygons into a resulting layer with merged overlapping polygons. It's hard to explain in words, so I've drawn a simplified ...
1
vote
1answer
100 views

How to extend lines in Grass

I have a set of vector lines in grass which I need to convert into polygons. However, because of bad base data, the polygons don't always close. To fix this, I need to extend each disjointed line by ...
2
votes
0answers
1k views

Simulate flood to assess Asset inundation footprints

I am trying to evaluate a number of flood gauges to assess at what levels of river height different flood risks would need to be issued. The gauges are currently set to warn of flood a couple of ...
5
votes
2answers
1k views

How to compare two DEMs and show their difference?

I want to compare my DEMs (ASTER GDEM2 and SRTM4.1). I know, that the GDEM has some extreme "holes" with totaly wrong elevations (I found 3 of them in my working area). Now I need to know, if there ...
0
votes
1answer
62 views

V.Digit Grass Error

I am trying to slowly switch from ArcGIS to GRASS but the interactive V.Digit tool is giving me a headache. I am trying to add supervised classifications training samples (i.e. polygons) for use in a ...
4
votes
2answers
559 views

How to enable GRASS plugin in QGIS 1.8.0 (Linux Mint 13 - 64 bit)?

Every time I enable GRASS plugin in QGIS (Plugins -> Manage Plugins -> GRASS), I got a message: Exception - G_getenv(): Variable GISDBASE not set. I googled and found some information here but don't ...
2
votes
3answers
436 views

Problem with v.in.ogr.qgis in QGIS

I received a shapefile containing data from a topographic survey of a farm. The file has a lot of lines containing elevation data. The person who made the survey did it with a GPS set up on a ATV. ...
10
votes
1answer
466 views

SEXTANTE toolbox - GRASS error

I am trying to use the SEXTANTE module GRASS (and SAGA) for vector analysis but whatever function I use I always get the same error:"Could not load layer: G:/closest.shp Check the SEXTANTE log to look ...
1
vote
1answer
556 views

Python script for GRASS - executing from PHP

I wrote the following python script: #!/usr/bin/env python import os import sys gisbase = os.environ['GISBASE'] = "/usr/lib/grass64" gisdbase=os.path.join("PATH") location=LOCATION NAME ...
1
vote
3answers
398 views

Determining gradient of road segment

I've a shapefile of roads data. It contains information about terrain of road segments, i.e., hilly, flat, undulating, etc. I want to determine gradient of every road segment. I know this might ...
3
votes
2answers
2k views

How to convert a point grid to a raster?

If I load the original .csv file, I then have a map of the African continent represented by 14069 data points covering it at 40x40km resolution. Each data point shows solar radiation means across the ...
8
votes
2answers
2k views

How to smooth large vector polygons from Raster

I have a landuse classification raster file (6 classes) of a large area. But I need it in vector polygons so I vectorised it. No problem so far, but the result is - of course - that every pixel is ...
4
votes
2answers
998 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
votes
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
vote
2answers
265 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
votes
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
443 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
953 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
299 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
votes
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
546 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 ...
3
votes
2answers
2k 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
508 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
votes
1answer
709 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
vote
1answer
76 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
387 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
964 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
537 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
365 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
1k 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
174 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
380 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
184 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
453 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
198 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 ...