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4

First you need to project your geographic coordinates to a cartesian 2D coordinate system, since affine transformations don't apply to geographic coordinate systems. You can apply an affine transformation from control points or from transformation parameters. The QGIS plugin asks you transformation parameters, but it is much more common for a user to have ...


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For some basic tutorials and exercises for GRASS, you can check this link which I think is a great place for beginners. There are also a couple of other sources which describe the r.walk and r.cost functions and their associated parameters in greater detail (although I'm assuming you have already read these).


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The problem might be with your rule file. When you use GRASS through QGIS, it will do something similar: Gather input parameters from you with a dialog box. Initialize a command line GRASS instance. Import the input file in a temporary GRASS location. Execute a script with your parameters. Export the result. Draw the result on canvas (if specified). In ...


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Sympy is inappropriate here (or very difficult to use). For geometrical calculations in 2D, the best solution is Shapely. But don't forget that GRASS GIS 6.4.x has the module grass.script (look at GRASS Geoprocessing in Python Script) and GRASS GIS 7.x, the new module pygrass. You can also use the general Python modules GDAL/OGR (osgeo) or Fiona to open ...


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Re-run the setup, change to advanced install and look if the package grass is selected. It should be selected automatically as dependency. If it is, look under Processing -> Options -> Dataproviders -> GRASS commands. The first item should be checked. Finally, make sure to switch to advanced interface at the bottom of the processing toolbox. You ...


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There is a related button in the startup screen (lower right): http://grasswiki.osgeo.org/wiki/File:Wxgui-startup-gnulinux.png which allows you to delete a location. Or simply delete the location directory like any other directory on your computer.


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What you refer to as half basins are often called hillslopes. I'm not aware of any tool in GRASS GIS that can extract these features from a stream network and a DEM, although it is possible that I have overlooked the correct tool. However, if you are open to using alternative open-source GIS then I can recommend the hillslopes tool in Whitebox GAT, for which ...


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Examining the content of the file .../.qgis2/processing/processing.log after running the processing toolbox command gives you the result: ALGORITHM|Fri Jan 09 2015 18:18:40|processing.runalg("grass:r.mapcalculator","/Users/mytiff.tiff",None,None,None,None,None,"round(A)","202086.577,205625.414407,88411.048,90534.3504441",0,"/Users/mytiffr.tiff") And if ...


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There is a helper script as well in the code: http://trac.osgeo.org/grass/browser/grass/trunk/imagery/i.atcorr/create_iwave.py It generates the filter function IWave.cpp template from the csv file.


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There is a QGIS tool which is designed to help remove sliver polygons: Vector > Geoprocessing Tools > Eliminate Sliver Polygons An alternative method which may or may not work (depending on your polygons and attributes) is to use the Dissolve function (Vector > Geoprocessing Tools > Dissolve) and select a unique attribute column for the dissolve field. I ...


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I'm also on OSX Yosemite using QGIS and GRASS, the GRASS shell in QGIS doesn't start, but it's hard to use anyways (It's hard to copy-paste, the font is hard to read and there is no cursor or command history). I start GRASS in the OSX Terminal, doing all analysis there, while I use GRASS in QGIS to export shapefiles into the GRASS database, and to load them ...


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You can use the QGIS plugin LRS for that. It accepts points not lying on the line, so you avoid the first step (snapping points to lines). This is the workflow: Based on both a line (routes) and a point (for calibration) layer, go to the Calibration tab. Select the line (pipeline) layer with its route field (a field that identifies routes, it's very ...


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Yes same problem here. What I did to speed up this process was to load SHP files in PostgreSQL and do clipping there. Not a perfect solution but faster for me since I quite powerful server behind it. And yes, this operations are slow. I hope this improves in the future.


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The following solution is feasible only if you have a limited, manageable number of large polygons. First save each polygon as a separate, single-feature shapefile. Then for each one, do the following. My method is to use the MMQGIS plugin to export the feature set as .csv nodes, then open the .csv in a spreadsheet, and do a custom filter for shape_id cells ...



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