Tagged Questions

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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5
votes
2answers
630 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
482 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
1answer
67 views

Is there a way to access ps.map in python?

i am wondering whether its possible using python interface to load layers and edit them in Print/Cartographic Composer without displaying, and finally export to PDF? something that can be done via ...
4
votes
4answers
410 views

How to generalize and vectorize a LandUseClassification raster file?

I want to vectorize that rasterfile with its 6 landuse classes. The classification is very noisy and have to be generalized before. The result should be a polygone vector file. I use SAGA, (GRASS) ...
1
vote
2answers
87 views

How to join polygons and lines vector maps from openstreetmap?

I am struggling with the data format OSM gives me: I want to use OSM data for routing, but all round-abouts and parking lots are not in the lines layer. They are situated in the poly(lines) layer. ...
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 ...
3
votes
1answer
188 views

Where to change GRASS GIS wxGUI language?

I use GRASS 6.4.2 on Russian version of Windows 7 x64. As I start wxGUI it is shown in Russian. But I don't like its translation and want to work with English interface. I have no clues how to solve ...
3
votes
3answers
208 views

Topographic correction (for land use classification) with SAGA or GRASS

Is there a module in GRASS or SAGA (or a alternative open program) to do a topographic correction of a landsat image to enhance the land use classification? Thanks! Martin
3
votes
1answer
339 views

Quantum GIS Affine

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 ...
3
votes
1answer
171 views

r.watershed analysis error from raster map being in different zone and unable to be opened

I tried running my DEM (geotiff) file through the r.watershed program by the GRASS GIS plugin of QGIS. I believe the error message results from a raster map in the different zone than the current ...
0
votes
1answer
413 views

Compiling Grass from Source in Ubuntu

Hi a while ago I drafted a semi-universal guide on how to compile GRASS GIS on Ubuntu. Because I had enough emails asking more details I thought to post it here for everyone and if possible to ...
1
vote
2answers
240 views

count features in polygon shapefile A that fall within each feature of polygon shapefile B

I have two polygon shapefiles, each of which contain multiple (possibly overlapping) polygons. Is there some way, using GRASS, to calculate the number of polygons belonging to shapefile A that fall ...
1
vote
2answers
471 views

How to access vector coordinates in GRASS GIS from python?

Is there a way to iterate over lines and their vertices using python? I'm new to GRASS GIS, and it looks like there are ways to read raster (for numpy), but I don't see a direct way to access ...
3
votes
1answer
356 views

Correct ASTER with SRTM or Topographic Map

I have a problem with my DEM again. I decided to use ASTER GDEM2 (for different reasons). ASTER GDEM2 have its problems, I know, and I dont want to discuss that again. I have to use it, because SRTM ...
3
votes
1answer
281 views

How to divide a polyline by intersecting isochrones

I have two shapefiles, the first representing a path (a polyline with a single category), the second representing isochrons from the same origin (point 0) which intersect the above mentioned path. I ...
1
vote
1answer
146 views

How to resolve GRASS error “Execution failed: 'gproj -p' ”?

I installed the WinGRASS-6.4.0-1-Setup.exe 55M from http://grass.osgeo.org/grass64/binary/mswindows/native/. I'm using a x64. After installation, I tried opening the demoLocation but it failed and ...
2
votes
1answer
212 views

How to overlay my interpolation within the boundaries of Quebec?

I am trying to create interpolated maps within geographical borders. I have the coordinates and values to the points I am trying to interpolate. I also have a map of the geographical land mass in ...
2
votes
1answer
540 views

How to create a Digital Elevation Model

How to create a DEM starting from layers shapefile "contour lines" and "shares"? which module of GRASS I need to use? thanks for yours responses....
0
votes
1answer
16 views

How do I add “padding” to features when applying d.out.file to map display on GRASS?

Thing is this. I've done up a script to automate some spatial interpolation and eventually output the interpolated raster and contour lines as an image of the map display. I'm doing this using ...
2
votes
2answers
127 views

River drain: r.watershed to vector is not working

I want to vertorize the result of r.watershed (accumulation). After using r.to.vect I got the message that I have to use r.thin before. So I did, but the message comes again and again. What I am ...
1
vote
1answer
264 views

Merge two maps with OR operation in GRASS

I have two vector maps. The two maps cover the same area but are split up into polygons differently (i.e. if you were to imagine one map placed above the other, the lines defining the polygons would ...
0
votes
1answer
104 views

error using GRASS v.proj

When I try to use v.proj to reproject my map from OSGB to GoogleMaps coord system I get this error.... Reprojecting primitives: pj_transform() failed: failed to load datum shift file ERROR: Error in ...
2
votes
1answer
208 views

Using nviz module in GRASS through qgis error

I'm an new user to qgis/GRASS and I've run into a problem with the nviz module. In trying to visualise a raster heat map created from vector contours in 3D using the nviz module in GRASS tools in ...
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
165 views

Can GRASS read Spatialite geometry fields?

I've looked at the question: How to import SpatiaLite data into GRASS? already. The links there talk about two separate tasks: Passing SQL to a Spatialite DB from GRASS and connecting to Spatialite ...
3
votes
1answer
382 views

Cell calculations; QGIS,GRASS,GDAL,SAGA

I recently asked a question about trying to calculate the slope over distance (manually) using QGIS, but then I came up with another way of solving the problem, but I would have to get some help for ...
2
votes
2answers
651 views

How to vectorize a Raster-Classification? (qgis, grass)

I classified my raster-DHM into elevation levels using colormap. Its not a "real" classification, just a colormap. So I cant vectorize the classes to get polygones for every class. Whats the best ...
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 ...
2
votes
2answers
596 views

How to delete a map from the GRASS interface?

I want to delete a map that I generated from GRASS. I tried removing a map from the "Map Layers for each display" tab in the GRASS GIS Layer Manager, but it only removed the map from the list and not ...
1
vote
2answers
443 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 ...
1
vote
1answer
134 views

hypsometric colors alà IMHOF, SYDOW or PEUCKNER

I need a hypsometric color-map to add it to my multishade-modell. (High Mountain between 800 and 4000m) There are a lot of differend typs explained in IMHOFS "Cartographic Relief Presentation". I want ...
4
votes
1answer
217 views

Multishading: bring them together to one Raster-Image

I made a multi-hillshade with 4 different light-directions and colors and stacked one above the other, each with its own transparency. Now I want to "save" the result in one raster-image. Whats the ...
4
votes
4answers
451 views

How to automatically plot intermediate contours with QGIS, GRASS GIS or SAGA GIS?

I'm mapping a steep mountain range. My main contour interval is 50 m and my intermediate contour interval is 10 m. In steep areas, the interval of 10 m is too small, so I need to leave ...
1
vote
1answer
173 views

mdenoise/r.denoise: How to

I want to use mdenoise / r.denoise but i cant get it working. I have Xubuntu 12.04 and Grass 6.4.1 GRASS tells me after installing the plugin: g.extension extension=r.denoise ...
2
votes
2answers
468 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
1answer
108 views

Why is GRASS not thinning a terraflow raster properly?

I want to convert a raster map encoding directional flows (the output of r.terraflow) to a vector map. I'm using r.thin to process the output. It terminates successfully with 0 pixels removed during ...
0
votes
1answer
235 views

GRASS and QGIS- “ not recognized…format” but it worked before

Prologue: I used my Ubuntu file viewing GUI to move data files around and "clean house" a bit. I started a new GRASS session and tried to add NED elevation rasters which I have successfully added ...
1
vote
1answer
166 views

r.sim.water G_malloc error

I've been trying to run r.sim.water on a 3 meter LiDAR-generated DEM I have, but keep getting G_malloc errors: r.sim.water --verbose elevin=meterDEM.final@Sediment_Simulation ...
2
votes
1answer
186 views

Silence user warnings for GRASS-PYTHON program

I've created a program that runs externally from GRASS v6.4.1, using python 2.6. It imports an ESRI shapefile, and exports a seperate KML for every polygon in this vector file. Polygons with ...
1
vote
1answer
75 views

mapping number of days a site is flooded from daily inundated areas maps

I have a set of daily inundated area polygons and would like combine them into one map that can give me a map showing the number of days a site remained inundated. I am unable to figure out any ...
1
vote
2answers
270 views

What I'm doing wrong with the command r.out.ascii in GRASS GIS?

I have raster in .bil format which I want to save in GRASS GIS with r.out.ascii. I get this result in .txt file: north: 1N south: 0 east: 1E west: 0 rows: 1 cols: 1 55537 I suppose it is something ...
0
votes
1answer
39 views

Does 'r.patch' act only on “loaded” rasters?

Can I run the GRASS command 'r.patch' on raster files which are not "loaded" into the current GRASS session? That is, rasters which are simply in my folder but not in a GRASS location & mapset? ...
3
votes
2answers
131 views

How to make the layer 2 use the same vector categories from layer 1?

I'm having some doubts concerning the layer mechanism. Creating a new layer (ie a new connection between a vector and a DB table), I've imported a vector (rivers) through v.in.ogr, then I've cloned ...
0
votes
1answer
96 views

GRASS importing same-name rasters fails

I have NED elevation data in 3 rasters. (That's how it downloaded from USGS NED page.) The files are named "61471006", "61471006_2", and "61471006_3". I succeeded in using the GRASS GUI and menu ...
0
votes
1answer
140 views

How to specify column names with v.in.ascii

I have managed to import a CSV file into a points vector file using GRASS v.in.ascii v.in.ascii --o input=test1.csv output=test2 format=point fs=, skip=1 x=2 y=3 z=0 cat=0 This is test1.csv ... ...
0
votes
0answers
109 views

Making a Bridge Classification tool in GRASS GIS

I'm working on a tool for classifying bridges with GRASS. I have been using examples online but I've come to a standstill as how to actually make this tool in GRASS. I have my raster of my area and ...
5
votes
2answers
1k views

How to return raster values based on polygon (shapefile) boundaries in QGIS?

How to return raster values based on polygon (shapefile) boundaries in QGIS? Is this an elementary question, because I am finding it hard....... Ideally I would like a neat workflow as I am likely to ...
5
votes
1answer
733 views

Open software tool or QGIS plug-in to make land cover classification

Is there any tool or plugin for QGIS/GRASS to make an automatic land cover classification from satellite imagery - based on CLC nomenclature for example? Of course, it will not be 100% sure but it ...
5
votes
2answers
448 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
2answers
186 views

How to select a subset of separate bands in GRASS GIS?

As you know landsat data has separate files for different bands. Creating a subset is a wise option to work on region of our interest. Therefore, I used this method to subset my image - d.zoom || ...

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