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.
36
votes
4answers
11k 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?
...
17
votes
3answers
2k 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 ...
14
votes
3answers
287 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 ...
13
votes
6answers
1k 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 ...
13
votes
3answers
961 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 ...
12
votes
2answers
1k 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 ...
11
votes
2answers
1k 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, ...
11
votes
4answers
2k 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
2answers
268 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 ...
11
votes
1answer
908 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 ...
10
votes
4answers
715 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 ...
10
votes
3answers
540 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.
...
9
votes
4answers
753 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
402 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
196 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
3answers
1k 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 ...
8
votes
3answers
1k views
How to do hydrological modeling in QGIS?
Can someone please direct me to a tutorial where I can learn more about hydrological modelling? I am particularly interested in learning how to model flooding using data from gauging stations along ...
8
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 ...
8
votes
1answer
472 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
523 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
4answers
721 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
2answers
137 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
1answer
485 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). ...
7
votes
3answers
201 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 ...
7
votes
2answers
454 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 ...
7
votes
2answers
601 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 ...
7
votes
1answer
637 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
1answer
284 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
302 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
242 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 ...
6
votes
4answers
423 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 ...
6
votes
3answers
1k 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 ...
6
votes
2answers
550 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
1answer
347 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
1answer
274 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 ...
6
votes
2answers
196 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
1answer
2k 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 ...
6
votes
1answer
635 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
1answer
295 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 ...
6
votes
2answers
340 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
votes
1answer
197 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
votes
3answers
314 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 ...
6
votes
1answer
235 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 ...
5
votes
6answers
366 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 ...
5
votes
2answers
560 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 ...
5
votes
2answers
464 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 ...
5
votes
4answers
1k 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 ...
5
votes
2answers
450 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 ...
5
votes
2answers
1k 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
3answers
784 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 ...
