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.
2
votes
1answer
59 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
264 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
194 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
945 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?
1
vote
0answers
40 views
GRASS error reading raster map: request for row 1 is outside region [closed]
I'm a rather inexperienced GRASS user, and am trying to use an addon module called r.geomorphon (see http://sil.uc.edu/downloads.html#software). I've managed to get it installed and am trying to run ...
2
votes
1answer
117 views
Raster Analysis - Identifying features from Raster
I have an IDW, tension spline and hill-shade rasters that show an archaeological landscape and from these rasters I want to identify new features which are seen in the landscape as depressions. And ...
1
vote
1answer
86 views
Undefined reference errors installing GRASS addon
I am trying to install the r.geomorphons GRASS addon (available from http://sil.uc.edu/pdfFiles/jarek/r.geom.zip) in GRASS. I tried on Windows but gave up and decided the best thing to do was to try ...
3
votes
1answer
61 views
Is there an easy way to taper huge amounts of drainage vectors?
I've performed hydrological analysis using r.watershed using GRASS and now I have some stream vectors for a large area. Next, I'm planning to taper these streams to varying width to make them appear ...
1
vote
0answers
28 views
How do you change units from meters to kilometres? [duplicate]
Possible Duplicate:
Using ‘gdalwarp’ in Python script for Grass
I wonder how i could fit my cells to 10 km... Therefore is in meters... and the resolution is different (0.16164). I need ...
1
vote
0answers
63 views
i.maxlik cannot read i.class output signature file
I'm trying to perform a supervised classification using i.class. I'm then using i.maxlik, but this is returning the following error:
GRASS 6.4.3svn (India_01):~ > i.maxlik group=test_group@test ...
5
votes
2answers
289 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 ...
2
votes
1answer
195 views
Is it possible to produce a decent looking shaded-relief map at 50K-scale-or-larger using SRTM3 DEM?
I'm trying to make a decent-looking shaded-relief map of a particular area in 50K-scale-or-larger using open-source tools. The best (and free) option I have for DEM data for that area right now is the ...
3
votes
2answers
549 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
1k views
Convert 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 - ...
1
vote
1answer
74 views
extract data from several images to different shapefile columns using GRASS
I am now working in grass and I want to extract raster values from several images to a shapefile. I have already created the columns in the .shp where the raster values will be stored but I am facing ...
7
votes
2answers
447 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 ...
1
vote
1answer
51 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. ...
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 ...
2
votes
1answer
46 views
What units are used in GRASS Rasterize?
What units are used in GDAL Proximity or GRASS Rasterize?
- 'new size' parameter
5
votes
0answers
205 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 ...
4
votes
1answer
179 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 ...
4
votes
2answers
386 views
New QGIS install can't find GISBASE
At QGIS startup I get the message: "QGIS couldn't find your GRASS installation.
Would you like to specify path (GISBASE) to your GRASS installation?" (Windows 7) No amount of rooting around the ...
6
votes
1answer
287 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 ...
3
votes
2answers
175 views
Using 'gdalwarp' in Python script for Grass
I'm writing a Python script that aims to re-project various LANDSAT tiles into a common projection and then import the tiles into Grass. The script at present is shown below:
#!/usr/bin/python
...
3
votes
1answer
149 views
How to reproject a raster to Winkel Tripel projection?
I'm trying to project a raster map (in ASCII grid format) from longlat to the Winkel Tripel projection. But I'm running into errors, for instance gdalwarp won't accept the proj-string.
$ gdalwarp ...
9
votes
3answers
392 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 ...
5
votes
1answer
163 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 ...
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 ...
3
votes
2answers
1k views
How to install add-ons in GRASS?
How do I install the r.inund.fluv script in GRASS? https://svn.osgeo.org/grass/grass-addons/grass6/raster/r.inund.fluv/
1
vote
1answer
433 views
How to use GRASS with HEC-RAS?
I am trying to use HEC-RAS for the flood modelling of my flood simulation. How do I use the text file output of HEC-RAS with the GRASS script r.inund.fluv?
2
votes
2answers
205 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
1answer
64 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 ...
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 ...
1
vote
1answer
47 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 ...
0
votes
2answers
89 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 ...
35
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?
...
2
votes
2answers
60 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
145 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 ...
1
vote
1answer
630 views
GRASS GIS: How do I run a batch (bash?) script?
I am in a GRASS database (in command shell), where I want to run a loop function. For example, I want to do an operation on many raster files that are in the database. I know this must be done through ...
0
votes
1answer
398 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
341 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 ...
2
votes
3answers
215 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.
...
2
votes
0answers
257 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
451 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
46 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 ...
2
votes
1answer
364 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 ...
1
vote
1answer
331 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
...
2
votes
2answers
525 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.
...
5
votes
2answers
622 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
477 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:
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