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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65
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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? ...
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 ...
8
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3answers
2k 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 v....
3
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1answer
4k 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 ...
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 ...
12
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2answers
5k views

How to compute parameters for QGIS Affine transformation?

I have a vector floorplan (DXF) that I've added to a blank project in QGIS using the Dxf2Shp plugin. I've been reading tutorials and StackExchange threads, but I can't seem to find out how to "...
8
votes
3answers
9k 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, ...
16
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3answers
5k 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 (...
6
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5answers
7k 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 I'...
5
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2answers
3k views

How to correctly install QGIS 2.8.3 with GRASS plugin on Ubuntu 14.04?

I already tried to install QGIS 2.8.3 using the procedure described on: http://www.qgis.org/en/site/forusers/alldownloads.html#debian-ubunt, but grass-plugin do not compare on plugin list! I tried ...
32
votes
5answers
11k 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 ...
4
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2answers
2k 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:
4
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2answers
5k views

Converting point grid to raster using GRASS?

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 ...
12
votes
1answer
2k 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 ...
6
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
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3answers
805 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) ...
2
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1answer
412 views

GRASS 7.1 (dev.) i.landsat.toar error

I am working with Landsat 8 image acquired in 2014. I am trying to convert the raw image (DN) to Top Of Atmosphere Reflectance/Radiance (i.landsat.toar) in Grass 7.1 (still under development). The ...
15
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3answers
3k 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, ...
5
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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 ...
8
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2answers
3k 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 ...
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 ...
8
votes
2answers
628 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 ...
3
votes
2answers
623 views

How to make GRASS 7 addon available in QGIS 2.12?

I stumbled across the GRASS-Tool i.segment but could not find it in my QGIS processing toolbox. I found out that it is an addon for GRASS 7 that I already installed in GRASS 7 standalone. How can I ...
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2answers
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install GRASS Addon in with QGIS

Win 7 QGIS 2.0 GRASS 6.4.3 Hi everybody, I want to install some GRASS-Addons to use them in QGIS. Therefore I run GRASS-Plugin in QGIS an open the GRASS-Shell type: g.extension GRASS opens then i ...
0
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1answer
3k views

How to use GRASS module to delineate watershed area?

Update#1:I changed to work under qgis 1.8, I only input the DEM file and run the r.watershed module, and I got this: I have a DEM file of one specified region, and I take the following steps to ...
-4
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1answer
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How to extract drainage line network from GRASS GIS and QGIS [closed]

Giving DEM as input is there any way to get drainage network? I am newbie to GRASS and QGIS ,provide any working examples in GRASS GIS and QGIS with procedure.
3
votes
2answers
3k views

QGIS GISBASE specify location

I am just a beginner at this QGIS and GRASS and I am using this QGIS 2.0.1 Dufour which throws a error at the startup that "QGIS couldn't find your GRASS installation. Would you like to ...
3
votes
1answer
215 views

GRASS via Processing Toolbox doesn't work in QGIS 2.8.3 on Mac?

I am quite new to QGIS and working with the external applications such as GRASS. When trying to launch a GRASS tool from the processing toolbox I get the following error: Missing dependency. This ...
3
votes
2answers
918 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
282 views

QGIS 2.10 with ubuntugis dependecies Grass issues Ubuntu 14.04

I saw in How to correctly install QGIS 2.8.3 with GRASS plugin on Ubuntu 14.04? how to get Qgis 2.10 running from the non ubuntugis repository with grass features but I'm still having problems with ...
2
votes
0answers
412 views

Problem loading output layer QGIS

Every time I run operations with temporary file output from the graphical modeler, I get the following error message: Oooops! The following output layers could not be open CLIP: C:\Users\Amine\...
1
vote
1answer
165 views

Adding items to DEM in QGIS

Working with QGIS and Grass I would like to produce a ZTV. I have the bare land DEM happily ready to go but would like to add buildings and woodland to the calculation. Can anyone please point me in ...
18
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5answers
2k 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. ...
12
votes
5answers
1k 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
4answers
3k views

How to find dead-ends in road network using ArcGIS for Desktop or GRASS?

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 ...
8
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5answers
7k 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 ...
8
votes
3answers
172 views

Why are the holes in my polygons not generalized?

I have one polygon layer with many holes. I would like to generalize it. I used v.generalize of grass. With it, I used chaiken algorithm. But, only the borders of polygons were generalized, the holes ...
4
votes
2answers
825 views

How to determine aerosol model value for i.atcorr in GRASS?

The i.atcorr module in GRASS requires aerosol model data to perform atmospheric correction using the 6S algorithm. It seems like I need a value from one of these parameters to continue: Estimate ...
3
votes
1answer
121 views

Get ID for each single v.to.points point in GRASS?

How do I get for each v.to.points point an ID in the database (DB). So far I splited the line (each 10m) but it returns only one DB entry for each original line. v.db.select line cat|Id|Name 1|1|...
1
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3answers
1k views

Problem with python script to control GRASS GIS from outside - How to import grass.script under Win 8.1?

I am working with GRASS 6.4.3 and python 2.7.6 under WIN 8.1. I am a novice with computer science and coding, and I have seen many posts including those:Is it possible to use GRASS GIS in Python ...
5
votes
2answers
1k 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
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 ...
3
votes
1answer
3k views

How to identify line intersection in QGIS when I have more than 2 lines?

I am trying to identify where overlaps exist between multiple shapefiles. I would use the intersect tool, but it only allows me to intersect two layers. I have over one hundred individual line ...
2
votes
1answer
2k views

GRASS Geoprocessing in Python Script

I´m trying to get some GRASS geoprocessig tools running in a python script outside GRASS. I´m able to import grass.script, but I´m not able to get the tools running yet. Does anybody know what I´m ...
0
votes
3answers
1k views

splitting a lines layer using points

I'm looking to accomplish a similar task to this thread: How to split a line at point positions? Using QGIS and the Processing and GRASS toolboxes available, I'm looking to split a vector layer ...
15
votes
4answers
2k 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
2k 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 ...
9
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1answer
724 views

Kriging on GRASS+R - cannot allocate vector of size 146.5 Mb

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). ...
6
votes
2answers
355 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
2answers
699 views

Creating contours for specific elevations

Input data: 1. an SRTM raster. 2. Point file of peaks. -Attributes contain ID, x, y, z and the elevation at which the peak is completely isolated from a neighboring peak. The output I want is a line/...