Questions tagged [grass]

GRASS GIS (Geographic Resources Analysis Support System) is a free, open source geographical information system (GIS) specialized in handling raster, topological vector, image processing, and graphic data. GRASS GIS is a high performance analytical GIS and remote sensing with focus on modularity. Users can process both day-to-day data as well as massive time series.

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6
votes
4answers
7k views

Dissolving 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 ...
65
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5answers
44k views

Building effective heat-maps?

Using ArcGIS, QGIS, 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? What ...
18
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5answers
7k views

Splitting raster into smaller chunks using GDAL?

I have a raster (USGS DEM actually) and I need to split it up into smaller chunks like the image below shows. That was accomplished in ArcGIS 10.0 using the Split Raster tool. I would like a FOSS ...
12
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3answers
19k views

Generating DEM from contour Shapefile using QGIS?

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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2answers
8k 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 ...
15
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2answers
12k views

Computing 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 "...
28
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7answers
29k 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 ...
10
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3answers
4k 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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2answers
6k views

Unable to run any GRASS 7 algorithms in QGIS 2.18.10 on Windows 7(64)

Running Windows 7 Professional (64bit) SP1. I have QGIS 2.18.10 installed from the standalone installer. The GRASS commands (161 algorithms) are present in the toolbox and seem to run ok. However the ...
8
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5answers
11k 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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1answer
689 views

Activating 'missing' standard GRASS utilities in QGIS Processing toolbox

I have been using QGIS and Grass for ages and while I've noticed this issue before, I've not been bothered by it until now. It is (hopefully) a bit of a noob question but when I open GRASS in the ...
7
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1answer
7k 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 ...
3
votes
1answer
2k 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 ...
44
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5answers
18k views

Smoothing DEM using GRASS?

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 because the area is near flat and the DEM is 90m in ...
11
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7answers
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QGIS 2.14.1 LAStools install error: “wrong value for parameter 'Msys folder'…”

I went to step 4 from How to install LAStools toolbox in QGIS guide and extracted LAStools to my C drive and just made the folder there. I can't do step 8 because it seems to already be in "advanced ...
5
votes
1answer
713 views

Error using grass v.clean: “ 'utf-8' codec can't decode byte… ”

I try running the v.clean tool using QGIS 3.4. As input I use a vector line layer (I checked the validity and everything is fine), but running the algorithm I get the following error: Traceback (most ...
3
votes
2answers
791 views

How to restore a scarp surface grid to calculate material loss

I would like to calculate the volume of material lost from a scarp like the one shown in the following image: Is there a way to do these calculations with open-source software such as GMT, QGIS and ...
18
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3answers
7k 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 (...
7
votes
1answer
7k 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 ...
6
votes
2answers
6k views

Installing QGIS with GRASS plugin on Ubuntu?

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 ...
9
votes
3answers
12k views

Creating parallel lines at particular distance from lines which are part of a shapefile

I am using QGIS 2.18 . I have shapefile which contains multiple lines. After processing certain data processing , I need to draw parallel lines at different distances from existing lines. For example ...
6
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2answers
3k 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:
12
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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
3answers
2k 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) ...
4
votes
4answers
3k views

How to calculate peaks in a DEM

How could I extract all peaks from a DEM (large mountainous area)? Peak means something like: a pixel which is sourrounded by other pixels with smaler elevation numbers in a area arround the "peak-...
9
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 ...
8
votes
2answers
2k views

Seeking open source alternative to ArcGIS 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 ...
6
votes
2answers
4k 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?
4
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2answers
2k 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 ...
10
votes
2answers
5k views

Seeking QGIS equivalent to Focal Statistics of ArcGIS Spatial Analyst?

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 (...
4
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2answers
7k 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 ...
1
vote
4answers
3k views

splitting a lines layer using points

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

Get results from using GRASS algorithms with the QGIS processing tool

I am trying to write a plugin in QGIS that uses at some point a GRASS algorithm : "v.split.length", accessible by using the processing class, and here is how I am using it : processing.runalg("grass:...
4
votes
1answer
2k views

Using Spyder IDE to develop python for Grass GIS, get 'ImportError: No module named grass.script'

I am trying to use Spyder IDE to develop a python script using python library from grass-6.4.3. I run the script below, and get ImportError: No module named grass.script I am using python 2.7, ...
3
votes
2answers
3k views

Specifying GISBASE location for QGIS install?

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 specify ...
17
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3answers
4k 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, ...
8
votes
2answers
2k 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 etc....
7
votes
2answers
3k views

Snap points to line and calculate chainage using Open source GIS

I have a line layer (representing a pipeline) and a points layer (representing valves) and I would like to calculate the chainage of the valves along the pipeline. I assume that I would first need ...
5
votes
2answers
2k views

QGIS 3.4 error: utf-8' codec can't decode byte 0xe8 in position 50: invalid continuation byte

I have the following error message every time I try to run a GRASS algorithm in QGIS 3.4. I unistalled the software and installed it again but I did not solve anything. Traceback (most recent call ...
4
votes
1answer
1k views

Get drainage basin of a polygon (with QGIS, GRASS or other FOSS)

Using a polygon shapefile and a raster DEM, I'd like to find a way to get the drainage basin of a polygon area — that is, the area of all cells which drain into or through the cells contained in the ...
1
vote
1answer
6k 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 get ...
0
votes
3answers
2k views

Using Python script to control GRASS GIS from outside?

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 ...
8
votes
3answers
704 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 ...
8
votes
2answers
4k 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
2answers
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 ...
5
votes
2answers
3k views

How to properly open an ASTER data?

Yesterday i downloaded an Aster L1B image from USGS's website. If i load it in QGIS, it doesn't get displayed properly(location wise). Even after i've enabled "On the fly" option, it's not reading the ...
16
votes
4answers
5k views

Manually correcting 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
votes
2answers
3k views

Cannot run Grass algorithms in QGIS 2.18 on Ubuntu 16.04

I have QGIS and GRASS installed through the UbuntuGIS repositories. If I try to execute any GRASS 6 or 7 algorithm I get the following error message: "This algorithm cannot be run :-( It seems that ...
4
votes
1answer
5k views

How to make GRASS and SAGA tools capable to use in QGIS?

I installed QGIS, GRASS and GDAL by OSGeo4w package, and as I finish the installation, I want to use GRASS tool, I face this problem: But I already installed GRASS and SAGA, how to make those tools ...
3
votes
1answer
1k views

Selecting point to obtain water basin leading to it

For the past few days, I have been working on building a watershed model including drainage basins and find that I am not looking for a global watershed and basin distribution, I am looking to ...