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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. ...

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4 views

how can interior basins be modified in the r.watershed GRASS function?

This is a follow up question to How does "Minimum Size of Exterior Watershed Basin" work in r.watershed command in qgis 2.18.12? I understood that the threshold parameter is used to ...
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35 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 ...
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39 views

Error using v.clean

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 ...
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0answers
44 views

Dissolving large sets of polygons [on hold]

We have many datasets, each containing about 150'000 polygons. We would like to dissolve each dataset down to about 2500 polygons, based on a given attribute. We've successfully done this using the ...
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23 views

Calculate the area of the drainage basin upstream of a point [duplicate]

I have the point location of vegetation surveys conducted on a river network. I would like to calculate the area of the contributing drainage basin upstream of each point using a DEM. This image ...
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2answers
24 views

How do I work with GRASS regions?

Every time I think I've started to get a very basic handle on QGIS, I get thrown for a loop. I tried to run r.flow today, and got the following error: ERROR: Elevation raster map resolution differs ...
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2answers
23 views

Cumulative cost upstream a raster stream network with GRASS

I have a river network in raster and locations of many dams on the river. In the image above, the BLUE point represent one random cell. Dam 1 is downstream to the cell. I am looking to calculate ...
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36 views

Fix original Indian constituency shapefiles lacking projection information

I found original Election Commission of India shapefiles containing constituency boundaries prior to delimitation using the Wayback Machine. These shapefiles are available here: https://web.archive....
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1answer
41 views

Getting WHERE statement to work in v.generalize?

I have a shape (its topology is terrible but I don't think it's the problem). I'm trying to simplify it to reduced it's size using v.generalise. I succeeded at reducing the whole shape but I ...
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39 views

Determining distance to nearest location along stream network by each cell using GRASS?

I have a river network in raster and locations of many dams on the river. In the image above, the BLUE point represent one random cell. Dam 1 is downstream to the cell. I am looking to calculate ...
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0answers
25 views

Batch distance calculation with v.net.distance

I have two point shapefiles one containing destinations the other containing postcodes. I want to calculate the distance between the postcodes and destinations with the help of GRASS v.net.distance ...
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28 views

“env: python3: No such file or directory” error using GRASS v.clean command in QGIS3.4.0 (on Mac OS Mojave)

I have a large number of vegetation shapefiles (~200) which have not been topographically cleaned up after digitising (lots of polygon slivers, gaps between polygons, and overlapping polygons). After ...
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1answer
9 views

Empty results from r.fuzzy.set in GRASS 7.4.2

I am trying to fuzzify a distance to roads tiff file using r.fuzzy.set in GRASS (installed with QGIS). I input the parameters (input layer, output, inflection points, fuzzy range, fuzzy boundaries etc ...
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23 views

Replace RGB value of a selected pixels with user input value in QGIS, grass or GDAL [closed]

I want to get selected automatically same RGB value pixels and replace with user input value in QGIS, grassGIS or GDAL. The imagery is grayscale or RGB unsigned 8 bit. For example- If I select ...
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1answer
41 views

Error - Grass 7 doesn´t run because isn´t not sucessfully installed

I am having problems to run GRASS7 from the processing tool. Always run the following error that is not corrected instaled. I ve reinstall QGIS several times, even tried different versions,as also ...
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19 views

Grass 7.2 error when processing and crash creating mapset

Try to run GRASS GIS in QGIS 3.4.o and getting this error. but also have another error when tro create new mapset, the _QGIS always crash. What should the origin of this problem?
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7 views

v.surf.idw attribute table column with graphical modeler

I want to use the algorithm v.surf.idw into the graphical modeler, how con i change automatically the attribute table column with values to interpolate? I have to interpolate data from different ...
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9 views

Exporting 3D Layer after Extruding Vectors?

I managed to extrude my vectors to the height specified as an attribute. SO now I see on GRASS GIS my city in 3D. I want to export this to an architectural software (Rhino or AutoCAD) but when ...
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61 views

Grass algorithm r.neighbors doesn't work in Qgis 3.4. How can I solve this?

When I try to run the algorithm it gives me this error: Traceback (most recent call last): File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\algs\grass7\Grass7Algorithm.py", line 411, in ...
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0answers
36 views

QGIS 3.4 macOS GRASS processing tools broken from fresh installation

Here is the error I get when running processing tools in QGIS 3.4 for macOS 2018-10-31T08:54:25 INFO GRASS GIS 7 execution console output WARNING: Default locale settings are missing. ...
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2answers
37 views

Breaking lines in PostGIS?

I have a roads table and I want to break the lines in the intersections like the v.clean tool from GRASS (I'm talking about how the break tool in the parameters works). How can I do the same process ...
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1answer
24 views

How do v.distance 'upload' parameters actually work?

I'm trying to use v.distance (using QGIS 3.4) to calculate the distance in meters between a layer of water shutoff points and the boundary of the nearest building footprint polygon. Even better would ...
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0answers
81 views

r.recode error with QGIS 3.4

Yesterday, I successfully ran the r.recode Grass-command from QGIS 3.2 Bonn on a Windows 10 machine to recalculate a DEM-geotiff. Today, I installed QGIS 3.4 Madeira and de-installed all older QGIS-...
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12 views

grass gis i.group tool

When perfoming supervised classification in GRASS, I get weird results where I single land cover class covers the entire images as below. I suspect it has to do with the images or bands put into the ...
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3answers
30 views

r.in.gdal tries to create file in incorrect repository

I am trying to import a DEM in GTIFF format with: r.in.gdal --overwrite input=$user_filename output=srtm_mosaik_utm -o but I get the message: Input contains an invalid SRS. WKT definition: LOCAL_CS[...
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1answer
30 views

supervised classification in grass gis

I am currently using GRASS GIS 7.4.1. I need some help here: when loading a geotiff made in QGIS to GRASS GIS, the bands that make the image are split (e.g.clip1@permanent, clip2@permanent, & so ...
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2answers
53 views

Splitting catchments in GRASS

I have the polygon of my catchment of interest, I call it catchment A (Reyran in the schema). (format *.shp). I have also the x-y coordinate of a dam that is situated in the catchment. I have also a *...
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1answer
25 views

Workaround for Intersection with points is not yet supported' GRASS Error

I am dealing with a line layer which I am unable to import properly into GRASS. After some work solving dangles and invalid geometry issues I managed to import it, nevertheless when I try to use v....
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1answer
35 views

Relating input data to output data in GRASS in QGIS 3

In QGIS 3 there are a number of useful vector tools available via GRASS functions. However, the output of many of these only contain 'cat' attribute in their output. For example, if I run the routing ...
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2answers
107 views

GRASS GIS Plugin not loading in QGIS 3

When starting up QGIS 3.2.2 (also tested with 3.2.3), I get the following message in the "Plugins" Log Message Window: 2018-10-18T08:03:48 WARNING Failed to load C:/OSGEO4~1/apps/qgis/plugins/...
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2answers
54 views

QGIS 3 r.texture no output

I cannot solve the mystery of no outputs in any case and in any experiment I have done with all kinds of parameters in the latest QGIS 3.2.3 Bonn and GRASS 7. r.texture does not provide any output. ...
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2answers
28 views

Specific methodology to call a GRASS function like v.transform with Python

I cannot understand if and how I can call with its parameters a GRASS function like v.transform through a Python script from e.g. PyCharm etc. Is there something comprehensible to understand? An ...
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2answers
46 views

GRASS algorithm in QGIS: v.to.lines

I'm using the v.to.lines algorithm (GRASS algorithm) to convert a layer from polygons to lines in QGIS. The algorithm works without problems but the output layer only has an attribute called "cat", I ...
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0answers
17 views

DLL error and 1073741511 error running GRASS from external Python script

I am struggling to run any GRASS 7.4.1 Session from outside using Python 2.7.15 with Spyder IDLE. While setting up the GRASS bin and GRASS environment are as follows are all good and showing no ...
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2answers
21 views

Purpose of comma in r.mapcalc in GRASS GIS 7.4

I would like to know the purpose of a comma in r.mapcalc of GRASS GIS. Consider this example - r.mapcalc "noise = if(landuse96_28m==1 || landuse96_28m==2, roads_buffers, null())" In the above ...
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34 views

Fixing invalid geometry of bathymetry level 0 of the world in EPSG:3120 projection?

I tried in different ways to validate the bathymetry of the world in EPSG:3120 from natural earth data in QGIS 2.18.13. Open the layer in QGIS and used Check Validity in EPSG:4326 and it was valid ...
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4answers
78 views

Have DEM, need polygon outlining region above a certain elevation

I have a DEM in HGT format. I need to isolate all areas above a certain elevation and view them as polygons. Something like this (let's say the pink polygon is everything above 1000m): Seems like ...
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1answer
40 views

GRASS v.qcount in QGIS is returning insanely high counts

I'm trying to use GRASS's v.qcount command through the QGIS processing toolbox to conduct a simple quadrat point pattern analysis. I've run the tool on some projected point data, but I keep getting ...
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1answer
37 views

Error when importing data source from web using GDAL/OGR in GRASS 7.4.1

I am running the latest bundle of OSGeo4W with GRASS 7.4.1 I am following the tutorial in the following URL: Analysing the ECA&D climatic data, where I am trying to import data from web using ...
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2answers
53 views

DEM from Vector to Raster in GRASS GIS

I am using GRASS GIS 7.4 and I have a DEM as points in a vector format and want to turn it into a raster. I tried using v.to.rast and v.to.rast3, but the elevation is not one of the attributes so am ...
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0answers
26 views

Error with QGIS and Grass Tools

I wanted to use the r.viewshed tool in QGIS. Everytime I want to start the tool there is a error (german): Dieser Algorithmus kann nicht ausgeführt werden run :-( GRASS GIS 7 ist anscheinend nicht ...
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1answer
50 views

Can't call GRASS commands with Python on QGIS 2.18

I'm trying to run a grass command (v.split.length) using the processing library in pygis. The script is as follows: import processing layer = r'path\to\shp.shp' extent = QgsVectorLayer( layer, '', '...
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1answer
26 views

Install GRASS GIS extension r.pi including r.pi.prox and implement the Addon in QGIS

I would like to install the GRASS GIS addon r.pi within QGIS, I only have access to basic GRASS commands I installed QGIS using the osgeo4w-setup-x86_64.exe advanced installation using the http://...
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0answers
48 views

Convert polygons to lines ignoring redundant vertices in QGIS

Provided the following Polygons layer with 6 polygons (see image below), I would like to calculate each line's segment's angle (amongst other things), so I should convert those six polygons into lines,...
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1answer
53 views

Extract a line segment out of a polyline on the basis of numeric values (distances) defined as attributes [QGIS]?

I have a set of points (red in the picture) in a shapefile containing an ID as well as two numeric values representing distances in Meters for each point. After creating polylines for each point via ...
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20 views

v.surf.idw raster file conversion into a vector with same colours style

Is it possible to convert from raster to vector the raster file resulting from grass interpolation algorithm "v.surf.idw" coloured with the quantile method and maintain such colours in the vector file ...
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0answers
71 views

How to automate topology check/fix in QGIS?

Short version: I have a layer with 19483 features with plenty of topological errors and I would like to fix/review them as many as possible in an automated way but don't know how to do it. ...
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1answer
34 views

GRASS: Can v.buffer use geodesic distance like r.buffer does?

Question: In GRASS GIS, can v.buffer use geodesic distance like r.buffer does? If v.buffer can't use geodesic distance, is there a way to do vector geodesic buffering (ideally in GRASS, but I can ...
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0answers
16 views

Grass(v.net.visibility): Performs visibility graph construction with only one point

Problem I would like to get the visibility of one point in regard to a polygon layer. E.g. which island can I see from the beach. What I found It's possible to get a visibility graph via Grass v....
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2answers
35 views

Issue with exporting GRASS visibility graph to shapefile

I am rerunning code in GRASS that has worked in the past (about six months ago) and am now having problems. In the GUI, I have created a new mapset and imported the 'SimplifedCoastline' file to the ...