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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128 views

Creating rasters?

I am doing my masters in archaeology, but have used GIS for some time now, however this is my first attempt at generating and using rasters. I appear to have been successful for some, but not so well ...
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2answers
106 views

Error using Grass v.net

I'm trying to connect my network to a points layer with a threshold of 4500 meters. I have about 11000 or so entries in my polyline and about 24 in my points layer. I have alreday used v.distance, ...
0
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1answer
258 views

How do I repair NVIZ error: 'Can't find a usable init.tcl'?

How do I repair the following problem: The error occurred while I was trying to run NVIZ in the GRASS environment in QGIS. NVIZ however runs perfectly in GRASS. On checking the directories ...
2
votes
1answer
614 views

How to delete rings automatically using QGIS/Grass

I'm cleaning up a (very) messy shapefile in QGIS/Grass. I now have several large polygons with numerous (100s) of small rings. Is there a quick and easy way to remove/ fill all these small rings. ...
2
votes
1answer
830 views

GRASS Geoprocessing in Python Script

I´m trying to get some GRASS geoprocessig tools running in a python script outside GRASS. I´m able to import grass.script, but I´m not able to get the tools running yet. Does anybody know what I´m ...
0
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1answer
67 views

GRASS v.db.update Concatenate Fields

I am trying to concatenate two fields into one new field in GRASS, but I am unable to get the syntax to work. Ideally, I would like "FIELD1" and "FIELD2" concatenated together in "FIELD3". All fields ...
4
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5answers
782 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 ...
3
votes
1answer
230 views

How to prepare road network for routing in QGIS or GRASS

I have been working on a road network and I want to run shortest path algorithms on it. One problem is that some lines come very close to each other, but are not connected. Is there a way to connect ...
3
votes
1answer
134 views

Issue with Sextante r.map calculator and modeler

I am trying to build a model with Sextante modeler and the r.mapcalculator algorithm but when I run the model I get the error message: ‘Could not load layer: ‘….’Check sextant log to look for errors ...
5
votes
1answer
397 views

How to call GRASS modules in pyQGIS?

I wish to use a Grass module (v.to.db) in QGis, without the grass toolbox. I tried with the Python console, but to no avail : Using Sextante plugin but obviously it didn't know all the grass ...
2
votes
2answers
366 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 ...
1
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2answers
319 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) ...
4
votes
3answers
313 views

How to install GRASS on Linux Mint?

I'm trying to figure out an error in GRASS network analysis, for several days now. I started to suspect that it has something to do with my OS, namely Windows 7. Hence I installed Linux-Mint 14 ...
1
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0answers
99 views

GRASS python script runs twice

Is there a reason that every script I have written for GRASS in python runs twice? I start them using the GUI script launcher tool, and they all begin with: #!/usr/bin/python import grass.script as ...
0
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0answers
719 views

How to resample a raster in QGIS?

I've got a boundary file that I would like to resample the raster file from a 30m grid to a 10m grid inside the boundary file. When I try and do it in Qgis or Grass all I get is one big raster cube ...
12
votes
1answer
1k views

How do you use GRASS's v.kernel?

I am flummoxed on how to use GRASS's v.kernel. I have a vector layer of around 2.5 million points. I want to make a heat map using v.kernel to show concentrations, since I have variable instances ...
1
vote
1answer
291 views

Installing GRASS on MINT 14?

I'm very new to mint/linux/GRASS and have no clue how to deal with these errors. Can I just change the URL somewhere? Here is the simplest reproducible command to produce a failure: sudo apt-get ...
1
vote
1answer
115 views

Set certain amount of pixels to 1 inside of a polygon (GRASS)

I have a rather coarse vector map with polygons and want to calculate a (sufficiently) finer raster map defined by spatial extension and resolution. Every polygon of the vector map has a value ...
9
votes
1answer
321 views

Is there a way to use ArcPy and PyGRASS tools in the same Python script?

I´m trying to write a Python script, that includes different ArcPy / ArcGIS commands and want to combine it with GRASS geoprocessing tools. Unfortunately importing the GRASS libraries doesn´t work. ...
1
vote
1answer
454 views

Raster operation with grass.mapcalc

I need to iteratively add each raster map of viewshed analysis obtained from a series of single observer locations. For this i used grass.mapcalc with Python (GRASS 7 for Windows). However, my ...
6
votes
1answer
361 views

Generalize large polygon-file

I have a large polygone file with landuse information (6 classes). Its vectorised from a raster classification so the polygons are all angular. Any of my tries to generalize with v.generalize (sneaks, ...
2
votes
1answer
435 views

Integrated viewshed analysis

I need to do integrated viewshed analysis of a target with several observer locations. I am going to use r.viewshed analysis function in GRASS. With this function, it is possible to perform analysis ...
7
votes
1answer
813 views

How to enable GRASS-modules in QGIS?

I have the latest QuantumGIS-1.9.0-master from Github with python-modules support and full GRASS-integration (GRASS-4.6.3-RC2) on Linux. When opening the GRASS-tools plugin, it only displays six ...
8
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2answers
2k views

How to correctly install QGIS with plugins and GRASS-integration from source?

I'm running a Sabayon GNU/Linux (based on Gentoo) at my home desktop system and I want to install Quantum-GIS. I'm currently using the qgis-1.7.0-package from the repositories. But this is somehow ...
1
vote
1answer
278 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 ...
3
votes
2answers
188 views

How to make the arrows in d.rast.arrow GRASS script visible?

I'm trying to create a Flow or directional raster map (with arrows) from an SRTM elevation map that I downloaded from CGIAR. I already created an aspectMap to be used for the d.rast.arrow. I used ...
1
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1answer
194 views

Grass r.mapcalc generates 1 cell map

I'm a GIS student and in my project I need to generate vegetation indexes. I've generated it succesfully yesterday using both python2.7 and grass gui .I'm using WinGRASS-6.5.svn-r54428-453 on Win7. ...
6
votes
2answers
560 views

Calling GRASS functions from external Python

I have GRASS 6.4.3svn installed in my machine running Windows 7. Also in my machine i installed Python 2.7.3 for Windows.Now i need to call GRASS libraries from Python and not within the Python shell ...
0
votes
2answers
211 views

How to install GDAL/OGR with GRASS vector support?

The GRASS 6.4.3Svn for Windows that i have in my machine does not have GDAL/OGR support. Is there any library (libgrass) for Windows to add into existing GRASS installation. If not, how to build or ...
2
votes
1answer
284 views

OGR Python bindings

When I try to access one of the GRASS vector files through Python OGR bindings, it gives error: Here is the script code in Python 2.7.3 IDLE (GUI) in Windows 7. from osgeo import ogr ds = ...
5
votes
1answer
239 views

How to create a heatmap using values?

How do I create a 'heatmap' in QGIS based on the values of the different points? I did do this once before with rainfall, but can't remember how!
3
votes
1answer
128 views

v.dissolve to multipolygon

Using v.dissolve in GRASS, I'd like to get a multipolyon as a result. However, I end up with distinct polygons with the same 'dissolve value.' For example; lets assume I have two polygon features ...
1
vote
2answers
795 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 ...
4
votes
3answers
8k views

Converting a .jpg map into a shapefile

I have a .jpg map of a set of U.S. counties that were affected by a tornado. The map shades where the tornado passed through, resulting in some counties only partially experiencing the tornado. I ...
13
votes
2answers
2k views

Is there a way to automate the preprocessing of LANDSAT data?

I'm currently enrolled in a remotesensing course, using LANDSAT data. Part of my course is about standardizing the scenes based on radiance values. I assume that because this is such a tedious task, ...
4
votes
1answer
2k views

Importing shapefile in grass

I have very simple shapefile, which consists of couple of polygons, and I wanted to snap boundaries automatically. Unfortunately qgis doesn't have such function, but grass has according this answer: ...
1
vote
1answer
310 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. ...
2
votes
1answer
202 views

How to filter or query data in GRASS?

I have a PostGIS dataset with just over 2 million rows. Each row has a PostGIS geometry point value and several attributes. I'd like to do some analysis on certain subsets of the data, but I can't ...
6
votes
2answers
505 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 ...
4
votes
1answer
81 views

How are r.horizon results aligned?

I used r.horizon to calculate horizon on a raster every 10° without any offset. I have got 36 files now. Is the first file from 0° to 10° (then centered on azimuth=5°) or is it centered on 0°, in ...
-1
votes
1answer
150 views

GRASS-QGIS Linking error

I need few customizations over grass and would use qgis gui for accessing grass. I am building qgis with grass enabled (WITH_GRASS=TRUE). While I am doing that I get the following. Any help is greatly ...
3
votes
1answer
102 views

How to recategorize features in GRASS by geometry, like the ArcGIS Sort tool?

The ArcGIS Sort tool creates a new feature class with features sorted by geometry. For example, it can number features IDs from north to south, etc. Is there a way to renumber the cat field in a GRASS ...
1
vote
2answers
548 views

How to import .flt files into GRASS?

I am trying to import a raster file (.flt) into GRASS. The raster file (.flt) was generated from HEC-RAS. The said raster format cannot be imported into GRASS (it shows the error "file not ...
1
vote
3answers
358 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 ...
4
votes
5answers
588 views

How to save a raster and vector into a single PNG file in GRASS?

I am trying to save a raster and vector into a PNG file. The vector is overlayed on top of the raster map. I was only able to save the raster file into a png using r.out.png but without the vector.
3
votes
2answers
282 views

How to determine aerosol model value for i.atcorr in GRASS?

The i.atcorr module in GRASS requires aerosol model data to perform atmospheric correction using the 6S algorithm. It seems like I need a value from one of these parameters to continue: Estimate ...
2
votes
1answer
108 views

How to close and fill Gulfs and inlets in QGIS or Grass?

I have a raster layer from which I extracted only zones with a certain color, then polygonized it with QGis. I just generalized the new vector layer in GRASS to smooth things a bit. There are many ...
2
votes
1answer
677 views

How to correctly merge layers with overlapping polygons in QGIS/GRASS?

I have 4 vector shapefile that I would like to join/merge, without worrying about attributes. Here are the shapefiles. I would like to do an union and a spatial dissolve, but everytime I do a dissolve ...
6
votes
2answers
267 views

How do I compute v.kernel maps in less than 16 hours?

I am using the GRASS GIS 6.4.2 bundled with QGIS 1.8.0, using a PostGIS dataset exported via v.in.org.qgis from QGIS, to create kernel density maps. The layer has 738,288 points. My problem is the ...
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?