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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51
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4answers
18k views

How to build effective heat-maps?

Using ArcGIS, QuantumGIS, Grass, and/or GVSIG What are some of the tools and processes involved in building effective heat maps? What are the plugins involved? What are the major data requirements? ...
22
votes
3answers
4k views

How to smooth a DEM?

I have a SRTM DEM and I want to create a shaded relief from it. I created the shaded relief in GRASS and the result is very nice, but a little rough becouse the area is near flat and the DEM is 90m in ...
18
votes
5answers
947 views

How to simplify a routable network?

I have a network graph that I need to simplify in the sense of reducing the number of edges. The idea would be to merge nodes that are located close together and remove the connecting short edges. ...
16
votes
4answers
688 views

How to do kernel density estimation with a physical barrier/ boundary in QGIS?

Does anyone know of a programme that will allow kernelling that takes a boundary into account in its calculation rather than simply masking areas that are impossible? So far I have found: GME add on ...
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 ...
14
votes
2answers
4k views

What's the relation between QGIS and GRASS?

I have been working with GIS and remote sensing in an university and professional environment some ten years ago (ArcInfo etc), so I have some experience even though somewhat outdated Right now I am ...
14
votes
6answers
3k views

What's the best way to produce a density map from weighted points in QGIS?

I'd really like to repeat the functionality of the ArcGIS Kernel Density tool - how could I do that? I would like to limit answers to easy-to-install free-and-open-source software – i.e. QGIS ...
14
votes
3answers
1k views

Rubber sheeting in GRASS or QGIS

We are in the process of getting our property boundaries corrected and a side effect of this is that we need to move any assets that have been drawn relative to the property boundaries, so they are ...
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, ...
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 ...
11
votes
2answers
926 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 ...
11
votes
5answers
988 views

Large shapefile to raster

I have a large shapefile (1 gb) and need to rasterise it. I have tried the following already. 1.) Import it into GRASS using v.in.ogr this failed with the error message: ERROR: G_realloc: unable to ...
11
votes
4answers
3k views

Shaded relief from DEM in GRASS and QGIS

I have been trying to get a good looking shaded relief model out of GRASS and Qgis for a day or so now and just can't seem to get it. The biggest problem I'm having is the valleys look like ...
11
votes
4answers
2k views

How to connect lines in a network?

I have a shapefile of lines and another of polygons. When two or more lines intersect a polygon they should be connected (snapped), but sometimes during manual digitization this doesn't occur. I need ...
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?
9
votes
4answers
2k views

Code to calculate elevation profile along line from a DEM

Given a DEM (Digital Elevation Model) say in and a line (x1,y1) --> (x2,y2) (paired coordinates (x,y)), how can one calculate the elevation profile or cross-section projected on that line ? I am ...
9
votes
4answers
1k views

Are there any open source tools to detect and fill sinks on a DEM?

Are there any open source or inexpensive tools to detect and fill sinks on a DEM? ESRI Spatial Analyst is just out of my price range.
9
votes
3answers
764 views

What are common methods for converting raster digital elevation data to vector contours?

In researching this I have found many references to the opposite, creating elevation data from contours, but nothing regarding contour creation. Preferably, I am looking for open source solutions like ...
9
votes
1answer
438 views

Import GRASS and SAGA modules to python script

I'm new at this. I am "building" a python plugin for qgis and I want to import modules from GRASS and SAGA but I don't understand how to do it. The plugin I want to import is Kriging interpolation ...
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. ...
9
votes
0answers
415 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 ...
8
votes
3answers
735 views

Howto setup and use a remote GIS workstation (QGIS,GRASS,PostGIS)?

I'm using QGIS (and sometimes GRASS and PostGIS) on my 2009 MacBookPro for my thesis project. I was wondering (during an endless batch generalizing in QGIS) if I can set up a server so I can work from ...
8
votes
3answers
2k views

R: Download a large DEM, change projection, and adjust to smaller scale

This is a process that takes just a few seconds in GIS software. My attempt to do it in R uses a large amount of memory then fails. Is there something wrong in my code, or is this just something R ...
8
votes
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 ...
8
votes
1answer
703 views

How to apply a Majority filter in GRASS GIS?

I was wondering if someone could help me write a majority filter for GRASS GIS. I have this map (see below) which I need to run a filter over to make the red areas a bit more dominant. I know I can ...
8
votes
2answers
737 views

How to convert a vector boundary to a raster map?

I need to output a PNG file of a raster map overlayed with boundaries present in a vector map. The problem is, the r.out.png script only exports a raster map. My boundaries are in a vector format. ...
8
votes
2answers
149 views

File naming for Enterprise GIS database?

I'm designing the guidelines for an Enterprise GIS database. Part of this database will include customized geoprocessing tools using a variety of software. I'm interested in knowing whether anyone ...
8
votes
4answers
992 views

Flood modelling insights

I am trying to create a flood modelling system. The system consists of two parts mainly a river flooding simulation and rainfall simulation. To do this I am running the latest version of GRASS 6.4. ...
8
votes
1answer
1k views

Open software tool or QGIS plug-in to make land cover classification

Is there any tool or plugin for QGIS/GRASS to make an automatic land cover classification from satellite imagery --- based on CLC nomenclature for example? Of course, it will not be 100% sure but it ...
8
votes
1answer
586 views

Kriging on GRASS+R

I'm trying to do a groundwater elevation map with an Ordinary Kriging on R, but always resulting on the lack of memory cannot allocate vector of size 146.5 Mb allocation (windows xp 32bit). ...
8
votes
1answer
738 views

How to pan-sharpen Landsat images for image-classification in GRASS?

I'd like to learn how to do an unsupervised classification of a Landsat scene using i.cluster > i.maxlik in GRASS using pan-sharpened 15m-resolution images (the example given in its Wiki uses the ...
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 ...
7
votes
4answers
957 views

Calculate polygon field based on neigboring polygon attribute

I have a vector shape with many different sized polygons each possessing an own class name (for instance "houses", "houses with offices", etc ...) I want to assign a new field to each polygon ...
7
votes
1answer
911 views

GRASS - Will r.to.vect work on this scanned map?

Total GRASS noob here. I have several very large hand contoured maps to digitize, and this thread intrigues me. In the past I have spent hours upon hours digitizing these maps and revisions in ArcMap. ...
7
votes
3answers
1k views

How to interpret GRASS v.kernel results?

GRASS manual reads: v.kernel - Generates a raster density map from vector points data using a moving 2D isotropic Gaussian kernel ... Ok, but how do I interpret the results? I understand that ...
7
votes
1answer
333 views

How to generate a DEM from isolines and spot heights?

I have two shape files containing height information of a certain area and I need to create a raster DEM with GRASS using them. file 1 consists of height information in contours (isolines) file 2 ...
7
votes
1answer
816 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 ...
7
votes
1answer
390 views

Saving Command History/Outputs to a file - GRASS

Is there any way to save the commands typed and the outputs obtained in terminal under GRASS GIS to a text file? I have read that GRASS saves history for each mapset but I have no much idea about how ...
7
votes
1answer
452 views

Why does GRASS eliminate polygons when using v.generalize?

I am facing a dilemma while trying to use v.generalize to simplify polygons which are similar in size and structure to US Counties or States. Often, I lose polygons from the data set after running ...
7
votes
1answer
294 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 ...
7
votes
0answers
658 views

GRASS v.Overlay/QGIS Intersect Speed intersecting line and polygon

Im currently trying to convert my scripts from ArcGIS to QGIS but one aspect that is extremely slow (imo) is trying to intersect a polygon with a line feature. I feel as though there must be a better ...
6
votes
4answers
1k views

How to find dead-ends in a road network

I'm trying to remove all the dead-end roads in a road dataset (lines) that are less than 100m long. How do I identify roads that are dead-ends (no exit)? The 100m part is easy. I know how to use Arc ...
6
votes
2answers
875 views

Moving raster to different mapset GRASS GIS

I have a raster DEM that I created in one mapset but I would like to copy it to another mapset for another purpose. Is this possible within GRASS or can I just copy some files over in the ...
6
votes
2answers
331 views

Is there an open source alternative to ArcGIS for Desktop's Integrate tool?

I need to snap about 1000 lines in one layer to the lines in another layer (there are about 5000 lines in the second layer). The lines to be snapped are about 15 map units away from the base layer ...
6
votes
6answers
403 views

Tool/Algorithm for generalizing OSM-Files for printing maps

Is there a tool or algorithm to (topological) generalizes OSM-shapes? I would like to build a printable map in different scales. In the image below you can see the same divided road (yellow) at ...
6
votes
2answers
1k views

creating a raster of the residuals of a regression between two rasters

I am trying to create a raster of the residuals of a regression between two rasters. i.e. I would like to carry out a regression of one raster against another of the same extent and plot the residual ...
6
votes
2answers
679 views

What's a good toolchain to reproject some PNGs in plate carre to UTM?

I have some PNGs produced from Canadian DEM data. They're 1201px by 1201px heightmaps. Each one represents one quarter of a degree latitude and one quarter of a degree longitude. But I want to work ...
6
votes
1answer
570 views

How to modify the colors of a raster map to use only one color in varying shades?

I have a raster map in GRASS containing elevation values. I want to display the elevation values in only one color (specificaly blue) but in varying shades of blue. I tried the options in r.colors, ...
6
votes
2answers
268 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 ...
6
votes
3answers
2k views

Dissolve or unsplit lines on common attributes in PostGIS or GRASS?

I have a road centerline shapefile that has roads split at every intersection. However, I would like to join LINESTRINGs that have a common set of attributes into a single LINESTRING. So long as the ...