QGIS is a user-friendly, cross-platform GIS application licensed under the GNU General Public License.

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8
votes
5answers
338 views

How to ensure uniform colour for DEMs?

This is a silly question, but one I've been trying to figure out for a while. I have two Aster DEM tiles, one next to the other. How do I ensure uniform colour for both?
8
votes
1answer
1k views

How to add a toolbar via python?

Through tutorials I learned how to add a toolbutton to the plugins-toolbar via python. Now I wonder how to add a complete toolbar with toolbarbuttons via python. Can anybody give some example-code? ...
8
votes
2answers
1k views

How can I create random points along a polyline in QGIS?

I am trying to create random points along a polyline shapefile in QGIS. Basically, like the 'random points' tool in 'research tools' but for polylines instead of polygons. I have tried converting ...
7
votes
3answers
758 views

How to count the number of lines connected to a point?

I have a water network which and I need to install elbows and Tees (T). When 2 lines connect to a point, I want to install an elbow, when 3 lines connect, I want to install a Tee. How do I get ...
7
votes
1answer
4k views

Best Way to Handle Many Raster Files in QGIS?

I have a project with a large number of raster files, but it is becoming very slow. I wonder which is the best way to handle all this. I'm simply georeferencing these files creating .wld file (geoTiff ...
7
votes
2answers
1k views

Is it possible to run an R script on a layer in QGIS?

I'd like to run an R script on a layer loaded in QGIS (to rotate a set of points created there using the Vector:Research Tools:Regular Points tool). I thought ManageR might work but cannot get it ...
6
votes
2answers
600 views

Split lines at intersection points

I've got some linestrings covering a road network, and need to split them at the crossroads. Does anybody have any idea on how to do it? I'm using QGIS 2.4, with a Postgis 2.1.3.
6
votes
1answer
1k views

How to transfer styles from QGIS to ArcGIS?

We have a QGIS project that has symbols for a lot of different lines. Data comes from a geodatabase that is accessible to both QGIS and ArcGIS. We now want to use the symbology of the QGIS project to ...
6
votes
2answers
3k views

Dissolve polygons in QGIS (GEOS) with tolerance

I have a polygon vector layer representing the area inundated in a flood. The layer has been produced in a such a way that some of the areas are composed of multiple smaller touching polygons (see ...
6
votes
3answers
545 views

Best practice in writing automated tests for QGIS plugins

I'm looking for some best practice advice on writing automatic tests for QGIS plugins written in Python. I have written tests for Python scripts in the past using PyUnit (the unittest module), but ...
6
votes
2answers
1k views

How to implement multivariate hex bins?

I have two point datasets that I am analyzing and I wanted to implement a multivariate hexbin approach for displaying this data. I have managed to cobble together an approach using QGIS SVG symbols ...
6
votes
3answers
451 views

Real-world QGIS users [closed]

I am just beginning as a QGIS user, and I have used ArcGIS mostly in the past. I am in the position of having to defend QGIS as a viable solution for many, if not most, GIS needs for Country and City ...
6
votes
2answers
4k views

how to create a new postgis database for usage with QGIS under windows

After installing postgresql with postgis under windows xp I have 3 databases: postgis postgres template_postgis now I try to create a new spatially enabled database in pgAdminIII: I select ...
6
votes
2answers
1k views

Support for PostgreSQL / PostGIS Inherited Tables in MapInfo/QGIS

Does anyone know if MapInfo and QGIS will support inheritance in a PostgreSQL/PostGIS database? I would like to make use of inheritance but need to make sure the software I use will work with them. ...
5
votes
2answers
239 views

How to define layer's CRS and avoid the CRS dialog in PyQGIS?

There is an existing Shapefile, which I want to add. At the moment my code looks like: self.iface.addVectorLayer(self.shpFilePath, "Track", "ogr") It works fine, but i want to define the crs ...
5
votes
1answer
131 views

How to connect centroids of lines sharing the same intersection in QGIS?

I'm looking for a big help to accomplish the following task: I have this street network of the center of Turin (IT), composed by lines representing streets, and black points representing ...
5
votes
4answers
1k views

Matching GPS tracks

I'm looking for a proper way to process multiple GPS tracks (so time ordered list of lat/lon points) and match/classify that segments, that are covered by multiple tracks: So it's not about ...
5
votes
1answer
529 views

How can I create a pollutant dispersion raster in QGIS?

As my previous questions have indicated, I am working on an air quality problem where I have a dataset of industrial emissions that consists of a location (long, lat), and an annual volume of ...
5
votes
1answer
3k views

GDAL VRT Format - do i understand the concept?

Okay, so im a little fed up with different raster-in-database solutions that I tried over the last 2 weeks which don't work currently (Postgis raster) or cant handle my volume of data (Rasterlite), so ...
5
votes
4answers
10k views

Delete points on a polygon using QGIS

I'm new at this, a novice at best. I'm using QGIS 1.7.3. I simply want to select a large number of points on a single polygon and delete them. Is this possible?
5
votes
4answers
2k views

How do I add (and map) a non-spatial table to QGIS from SQLite?

I have an sqlite file from my Wigle Android app (wiglewifi.sqlite). It's not a spatial file, just tables with lat/lon and other data. I can add spatialite layers just fine, but cannot seem to find a ...
4
votes
4answers
295 views

Checking if polygon fits inside another polygon using ArcGIS or QGIS?

How do I check if one polygon fits inside another polygon? Furthermore how do I automatically check if one polygon fits in other polygons of my shapefile? I have a shapefile with thousands of ...
4
votes
1answer
249 views

Adding new menu item to QGIS Desktop app

I need to add new menu item to the top level menu of QGIS Desktop (2.7.0); I.e. it shall be on same level as "Project", "Edit", "View", "Layer" etc. As far as I know there is pretty nice way how hide ...
4
votes
1answer
525 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 ...
4
votes
1answer
353 views

Raster to vector with gaps in Landsat ETM

I need to find size of water area from a raster (jpg) using QGIS 1.8.0-Lisboa. The raster is a Landsat image with gaps of data in it. I used Polygonize, but the output file shows wrong polygon size ...
3
votes
2answers
300 views

How to handle PostgreSql 1:m relationship data by using “Data-Driven Input Mask” QGIS plugin?

I have 1:m relationship tables in my PostgreSql. I like to show the main table attributes as well as the relational table attributes (like grid rows) in QGIS attribute-edit-form. What are the entries ...
3
votes
1answer
586 views

How to draw a simple bus network that works with pgRouting?

What I'm I doing wrong? I've created a new shape layer for lines, I've enabled snapping with 5 map units for that layer. When I draw a line between two of the stops I get a purple marker when I'm at ...
3
votes
1answer
4k views

How to manually edit point coordinates in QGIS?

Is there a tool for shapefiles or a QGIS plugin available, which will enable me to edit the coords of a point manually ? ("tool" -f1 "Tsunami Gauge"-move x1.abcdef -to x2.ghijkl) I do have ...
3
votes
2answers
2k views

1'' DHM: Hillshade is too rough - how to “generalize”?

I got this hillshade from my DHM (I used the hillshade-module from qgis). For my purpose there is too much relief detail (roughness). How can I get rid of this in QGIS or GRASS? Thanks! Martin
3
votes
3answers
2k views

Writing a plugin for Qgis using python to access PostGIS and write geometries

Sorry about the strange title didn't really know how to word it. I currently use MapInfo to do most of my GIS work however I have recently installed PostGIS 1.5 and am really liking it so far. A ...
2
votes
1answer
285 views

How to keep georeferencing from ArcGIS when importing raster into QGIS?

I tried searching for the answer to this, but I didn't see anything, so here it goes: I have previously georeferenced some .png raster images in ArcGIS 10.2.2, and could like to import them into ...
1
vote
2answers
460 views

How to use SEXTANTE in a script outside QGIS?

I´m trying to do some geoprocessing using the QGIS Sextante plugin outside of the QGIS application (and integrate it with different other libraries like arcpy, etc.). import sys, os from PyQt4.QtGui ...
15
votes
2answers
4k views

How to select features with NULL attributes in QGIS?

I need to identify which features have null attributes in the attribute table of a shapefile. When i try [field]= 'NULL' it selects the features with value=0 (see picture) Suggestions?
14
votes
1answer
413 views

How to query OSM for all beaches facing west? - QGIS preferred

I want to identify all beaches on this planet (or a given subset of it) that are facing westwards (+/- 20-30 degrees). My idea is to use OSM as the data source. Extracting all polygons that have the ...
13
votes
4answers
4k views

Shaded relief from DEM in GRASS and QGIS

I have been trying to get a good looking shaded relief model out of GRASS and Qgis for a day or so now and just can't seem to get it. The biggest problem I'm having is the valleys look like ...
11
votes
1answer
7k views

How can I uninstall Quantum GIS that was installed using OSGeo?

I installed QGIS using OSGEO4W, and would love to know how to uninstall it, because when I go to "Control Panel > Programs > Uninstall" the program does not appear in the list of installed programs. ...
11
votes
2answers
462 views

How do you protect your PostGIS credentials when using QGIS 1.7?

I'm fairly certain this should be a community wiki, but I don't know how to make it one. So if an admin sees this please change if appropriate. So.....How do you protect your PostGIS database data ...
9
votes
1answer
340 views

How to call the interpolation plugin from the python console?

I would like to call the QGIS interpolation plugin function (TIN method) (Raster->Interpolate) from python console. I can't find the corresponding function within QGIS API or within the ...
9
votes
3answers
789 views

How to Display Overlapping Lines?

I have multiple line layers that represent bus routes and many of the routes overlap (i.e. near terminals, transfer locations, etc.) Is there a function in Qgis which will display both features ...
9
votes
1answer
662 views

How to view a 155 MB raster stored in PostGIS?

I am using the following command to load a raster into a postgres database: raster2pgsql -I -C -e -Y -F -s 3086 -I -C -M myraster.tif myraster -F -t 30x30 | psql -U postgres -d database -h localhost ...
9
votes
5answers
2k views

How to run sextante algorithms outside of qgis python console?

I'm kind of stuck trying to figure out the way to run sextante from a standalone python from OSGeo4W distribution. The reason I want to do this is that I got tired entering parameters in the dialog ...
9
votes
1answer
1k views

How to add features to a PostGIS layer using Quantum GIS?

I am using Quantum GIS and the PostGIS dbms. I am able to call the PostGIS layer into QGIS but i am unable to add feature to it. I am using the method of adding features to a Shapefile but still it is ...
9
votes
3answers
6k views

How to control Image Output Settings in QGIS?

I am exporting a QGIS map to an image format. I would like to have control over the output settings of the image (dpi), as currently it is only exporting the images at 96 dpi. Does anyone know if this ...
8
votes
1answer
299 views

How to visualize measure values along linestrings in QGIS?

I have a series of LineStringM geometries. The measure value represents slope (or stream gradient) at each point in the geometry. I love QGIS's robust styling options, but I can't find a way to render ...
8
votes
2answers
1k views

Building FGDB support for GDAL 1.10 on Ubuntu

Because data.gc.ca is now distributing some of its data in FGDB format (example: Plant Hardiness Zones), I would like to be able to use it with gdal/QGIS. The compile/install is not going as planned, ...
8
votes
4answers
2k 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
votes
7answers
5k views

Extract boundary from detailed layer in ArcGIS Desktop or QGIS?

Is it possible to return the boundary (outside) permiter of a polygon layer? Let's say you have the map of the USA, for simplicity, broken down to the county level, is it possible to return the ...
7
votes
3answers
3k views

How to extract slope from topographic raster map?

I am working on a project for a machine learning class wherein I extract features from a topographic raster map and then classify the traversability of the terrain. One of the features I need to ...
7
votes
1answer
914 views

How to call GRASS modules in pyQGIS?

I wish to use a Grass module (v.to.db) in QGis, without the grass toolbox. I tried with the Python console, but to no avail : Using Sextante plugin but obviously it didn't know all the grass ...
7
votes
4answers
14k views

How to export highlighted features from attribute table to an excel file?

When i selected some portion of the map in QGIS, in the attribute table the selected features gets highlighted... How to export the highlighted features from attribute table to an excel file ...