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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109 views

How do I count the number of vector lines that pass though a given raster cell?

I am working on a project (currently in GRASS7 though I'm not against exporting to Arc or R or other software if necessary) where I am generating thousands of shortest cost paths (using the r.walk and ...
7
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2answers
963 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 ...
7
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4answers
5k 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 ...
7
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1answer
2k 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
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1answer
5k views

How to create a point along a line given distance

I have been given a non-spatial database which contains the names of lines which I have a shapefile for. The database also has names of points and the distance of each point from the origin along the ...
7
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2answers
151 views

Remote geoprocessing solutions?

I have a relatively old laptop (i5 8Gb) but it is fine for most of my GIS needs. Infrequently I would like to run processes which requires larger amounts of RAM (16G+) but I cannot justify forking out ...
7
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2answers
7k views

How to generate a DEM from a contour Shapefile?

I want to create a DEM from depth contours (shapefile) in QGIS. I've been trying to work out how to do this based on this previous question, notably from this link from that page, however I'm stuck, ...
7
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1answer
1k views

Calling 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 ...
7
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3answers
509 views

Grass v.rast.stats returning null values

I have a vector layer (polygon) and a raster layer. The raster layer holds values for height above bald earth in a field called "value". I'd like the vector layer to inherit either the mean or the ...
7
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1answer
1k views

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

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 ...
7
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1answer
393 views

How to create a topologically correct dataset in PostGIS (with GRASS)?

I have shapefiles which I have loaded in postgis and now i am trying to use geometric function in postgis like ST_intersect and they fail because the data is not topological correct. I have tried to ...
7
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1answer
987 views

How to perform unsupervised classification of LANDSAT time series using Grass?

I'm using GRASS to perform an unsupervised classification on a time series of LANDSAT images (monthly temporal res, over 30 years), in order to compare land cover change in a particular area. I'm ...
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5answers
5k views

How to set all pixels with value <= 0 to “nodata” in DEM raster?

I have a DEM raster with pixel values between about 3000 and -0.0003. I need to set all pixel with a value of 0 and smaler (<=0) to "nodata" (for later raster calculations and to reduce the ...
6
votes
6answers
1k views

Southern hemisphere projections for Landsat upsets GRASS

Hi All does anyone have the last word on why Landsat scenes don't project in the southern hemisphere. This causes no end of trouble in GRASS, less so in QGIS. What I mean is, take an original scene ...
6
votes
6answers
880 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
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2answers
1k 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
5answers
5k views

How to calculate distances in a point sequence?

I'm looking for help calculating the distance between a sequence of points that are in a single Shapefile in QGIS. Below is what my data look like and a blank distance column I've added to show how ...
6
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2answers
2k 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
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2answers
868 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
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2answers
154 views

Skeletonize vectors in QGIS/Python

I am trying to find a tool to create a skeleton of a large vector dataset using QGIS and its bundle. It should be directly programmatically callable through Python or commandline (QGIS, GRASS, OGR ...
6
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3answers
10k views

Viewing .las format LIDAR data in QGIS?

Is there an easy path to visualizing this LIDAR data? I have QGIS, and some USGS LIDAR data in (.las) format downloaded from http://lidar.cr.usgs.gov/ . This means I have both the (.las) and ...
6
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2answers
937 views

Raster to Vector: Displaying classes in Vector Layer - GRASS GIS

I use Maximum Likelihood classification to classify Landsat image into two landuse classes - one of my interest and rest including all others. Inorder to assess the accuracy I export it in vector ...
6
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1answer
920 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
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2answers
338 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
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3answers
1k views

Cutting out depth information in raster. Calculating volume in Qgis

I am trying to calculate habitat volume for around 30 fish stocks in Qgis. I have habitat areas (shape files) and Bathymetric information (.tif file). I believe I can calculate the entire volume of ...
6
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1answer
7k views

Converting Shapefile to MySQL?

I have used Grass GIS imported a .shp file; I now want to export this file to MySQL. I understood that MySQL will contain the function of all three the files necessary in a Shape file system (.shp - ...
6
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1answer
1k views

How to calculate difference in altitude along lines using GRASS?

Using SRTM altitude information and OpenStreetmap roads, I want to calculate altitude differences (sum of meters uphill and downhill separated = two values) per road element. What would be the ...
6
votes
2answers
2k views

How to compile QGIS with GRASS on Ubuntu?

I am on Ubuntu building qgis with grass plugin. I have build grass code separately and used --prefix to provide the path GRASS_PREFIX is /usr/local/grass-6.4.2 and GRASS_INCLUDE_DIR is ...
6
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2answers
776 views

Is it possible to use the Goode Homolosine projection in QGIS?

Is it possible to use the Goode Homolosine projection in QGIS? Both QGIS and GRASS seem to have trouble with the interruptions, squashing the higher latitudes together. I tried +proj=goode ...
6
votes
1answer
566 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 ...
6
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2answers
577 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 ...
6
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1answer
140 views

Would it be possible to construct a stand-alone grass.script python package?

I would like to migrate dependency on ArcPy to grass.script without requiring the full installation of Grass. Would it be technically possible to have a portable directory containing grass.script and ...
6
votes
1answer
206 views

Cell declustering using open-source software

I want to perform cell declustering in a small point data set. I have 9 observation points and I want to find the size of the region of influence for an observation, and afterwards use that as ...
6
votes
1answer
615 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, ...
6
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0answers
156 views

Can GRASS compute the line graph representation of an input graph?

I'm interested in computing a line graph for an input graph, preferably in GRASS since I'll be using other GRASS network analysis tools afterwards. I couldn't find any reference to line graphs in the ...
6
votes
1answer
344 views

Using GRASS algorithms in Sextante under ArcGIS Desktop?

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 Desktop? I tried to look ...
5
votes
3answers
596 views

LiDAR data density, returns per square meter

How can I compute a raster showing the number of return points per square meter using SAGA GIS or other open source software? My goal is to obtain a mask which would show me the places (cells) ...
5
votes
2answers
1k views

How to delete a map from the GRASS interface?

I want to delete a map that I generated from GRASS. I tried removing a map from the "Map Layers for each display" tab in the GRASS GIS Layer Manager, but it only removed the map from the list and not ...
5
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3answers
612 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) ...
5
votes
1answer
2k views

Create filled contour map with GRASS

Background I'm trying to make contour/isoline/isochrone maps to show what areas are within walking distance to schools for my pet project to help with the Safe Routes to School program. I followed ...
5
votes
2answers
2k views

How to return raster values based on polygon (shapefile) boundaries in QGIS?

How to return raster values based on polygon (shapefile) boundaries in QGIS? Is this an elementary question, because I am finding it hard....... Ideally I would like a neat workflow as I am likely to ...
5
votes
4answers
3k views

How to reclassify a float raster?

I have three rasters which represent distance (in metres) from certain things (bus stops, parks, libraries). I would like to reclassify these rasters so that they get integer values based on the ...
5
votes
2answers
2k views

Is there a Focal Statistics (spatial analyst) tool in ArcGIS equivalent in QGIS?

I'm attempting to use QGIS v2.0.1 to accomplish the same tasks that I can do using ArcMap v10.1 and I'm running into some trouble finding equivalent tools. In ArcMap I am using the Focal Statistics ...
5
votes
2answers
762 views

Is it possible to use GRASS GIS in Python stand alone scripts?

I am trying to find a least cost path script for Python. I came across r.drain from GRASS GIS. Is it possible to use GRASS GIS in a Python stand alone script? If so where can I download the bindings?
5
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1answer
312 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!
5
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2answers
1k views

How to batch import GDAL supported raster files into GRASS?

I am trying to import some GDAL supported raster files into a binary raster map layer using the r.in.gdal module from QGis Grass tool. As I have multiple files to import, I would like to batch import ...
5
votes
2answers
2k views

How to color-balance false-composites of pan-sharpened Landsat images in GRASS?

Whenever I try to pan-sharpen composites of some Landsat images in GRASS using i.pansharpen, i.fusion.brovey or the IHS sharpening method, the output will have some or all of the following ...
5
votes
2answers
2k views

Quickly create contour polygons from cost points using OSS for web app

This is related to a previous question I've asked: Create filled contour map with GRASS I've created a point layer using OpenStreetMap data and pgRouting's driving_distance() function, where the ...
5
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2answers
811 views

Monthly Average Solar Maps (R.Sun) in Grass

I'm trying to create monthly average maps as described in R.Sun in Grass. I have my DSM. In reading the page on OSGEO it mentions that it is possible without showing how. Ideas? I assume I will need ...
5
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1answer
723 views

Calculate flow path with QGIS

I am trying to replicate my erosion model in ArcGIS for Desktop in QGIS 2.4. I tried to calculate the upstream distance along the flow path for my agricultural field using QGIS. I did the equivalent ...