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?
...
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 ...
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 ...
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 ...
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 ...
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 ...
3
votes
1answer
203 views
How do I find vector line bearing in QGIS or GRASS?
How can one extract the bearings from a set of lines in a vector file?
I'm trying to find the bearings of several straight vector line segments (simplified contour lines, actually) and can't figure ...
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 ...
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 ...
5
votes
5answers
454 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 ...
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, ...
2
votes
2answers
2k 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 ...
2
votes
2answers
989 views
How to convert a point grid to a raster?
If I load the original .csv file, I then have a map of the African continent represented by 14069 data points covering it at 40x40km resolution. Each data point shows solar radiation means across the ...
4
votes
1answer
888 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 ...
3
votes
2answers
182 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
287 views
How to get the Flow or directional raster map using GRASS?
Aside from using r.fill.dir in GRASS, is this the script to produce the Flow or directional raster map? Is this the output for the script ...
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 ...
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.
...
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 ...
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 ...
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
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 ...
4
votes
4answers
925 views
Where can I find a tutorial for installing an addon to GRASS GIS that a six-year-old could understand?
I want to use the r.stream.distance addon in GRASS GIS 6.4 on ubuntu 10.04 (64 bit).
I've installed grass from the repositories and that works fine but I can't seem to figure out how to install this ...
2
votes
0answers
262 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
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 ...
4
votes
2answers
486 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:
1
vote
2answers
444 views
Interpolation of contours (from one “main-contour-shapefile”)
I calculated, that the best and smalest possible äquidistance (equidistant) for my map is 30m. After I generlized my DHM, I extracted contours of a intervall of 30m and smoothed them. Now I have my ...
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 ...
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 ...
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 ...
5
votes
4answers
1k 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 ...
5
votes
1answer
961 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?
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
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 ...
4
votes
1answer
1k views
Convert shapefile lines to a polygon in GRASS
I have a shapefile of a map that is the outline of a number of islands. I would like to convert the lines into polygons (ie all islands filled in) using GRASS. I searched on how to do this with GRASS ...
3
votes
1answer
101 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 ...
3
votes
1answer
286 views
How to make a transparent background image using r.out.png?
Can the white background of the r.out.png of GRASS be changed to transparent?
3
votes
2answers
2k views
How do you Turn on the Grass plugin in Quantum GIS?
I downloaded and installed Quantum GIS 1.5.0 with Grass using the OSGeo4W installer on my XP machine. Unfortunately, when I go to Plugins>Manage Plugins I cannot find the Grass plugin. When I browse ...
2
votes
2answers
530 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.
...
2
votes
2answers
474 views
1'' DHM: Hillshade is too rough - how to “generalize”?
I got that hillshade from my DHM (I used the hillshade-module from qgis). For my purpose there a too much relief details (roughness). How can I get rid of them in QGIS or GRASS?
Thanks!
Martin
2
votes
2answers
336 views
r.mapcalculator and python again
I've been trying to write a script creating binary maps:
a=raw_input ("enter a threshold")
b=float(a)
grass.run_command('r.mapcalculator', formula="**'base_map'>=b**", outfile='map'+str(a), ...
2
votes
1answer
417 views
How to import SpatiaLite data into GRASS?
How can I import SpatiaLite tables into GRASS? Are there any restrictions I should be aware of? How does GRASS cope with columns that don't have a specific type (Sqlite tends to create such columns ...
1
vote
1answer
124 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 = ...
1
vote
2answers
1k views
How to set cell size for vector to raster conversion in QGIS GRASS plugin?
I'm converting a vector (loaded in GRASS plugin in QGIS (1.7.0.-wroclaw) and would like to convert this to a raster with a defined cell size. At the same time I need a value from the attribute tabel ...
1
vote
2answers
404 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
1answer
324 views
Win7 GRASS 7 & i.landsat.toar
Hello has anyone got experience running i.landsat.toar ?
The output files I get are empty, the command takes but a moment to complete. However when run in verbose mode all the calculations are done, ...
1
vote
2answers
322 views
GDAL-GRASS building fails
When I run ./configure --with-grass=/usr/local/grass-6.5.svn/ I get the following errors:
..........
checking for gdal-config... /usr/bin/gdal-config
using /usr/lib/gdalplugins as GDAL shared library ...
1
vote
1answer
705 views
How to select a raster file that is under a polygon in a vector file?
I am using:
v.db.select map=PHL_adm1 where=NAME_1='Bulacan'
My vector map is over the raster map. I want to select the part of the raster map under the polygon(NAME_1='Bulacan') of a vector. Is it ...
1
vote
1answer
1k views
How to combine a vector and a raster file?
I want to combine a raster and a vector file. After combining, can I query on the resulting map to obtain a specific area? How?
