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

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2
votes
2answers
50 views

Display two-dimensional color gradient for two different quantities

I have two overlapping raster layers. One contains quantity A from 0 to 100, and the other contains quantity B from 0 to 100. I'd like to create a map displaying both sets of data at once based on a ...
1
vote
1answer
271 views

How to export a geojson file with correct order of coordinates?

I was testing rendering of data via GitHub in geojson format, because I wanted to use it for INSPIRE data. INSPIRE data are in GML 3.2.1 format. I've downloaded one of datasets from ...
1
vote
2answers
98 views

How to exactly georeference in QGIS

When I georeference a raster image in QGIS, it's always a bit displaced as in the attached image (the cyan polygon is the template, the red border is the georeferenced image), although I try to set ...
0
votes
1answer
49 views

Creating a new shapefile based on an existing problematic shapefile

I have a large floodplain shapefile and would like to create a new shapefile based on coverage. I'm having major problems with the original (intersections and other errors) which I've been unable to ...
0
votes
0answers
5 views

How to programmatically interrupt QGIS initialization and startup

I'm wondering how to interrupt the initialization of QGIS 2.0 on Windows XP before start up. I've put a dialog in one of my plugins that shows up on start up. However, I'd like to make a quit button ...
0
votes
0answers
41 views

Lat Long to Useable values in QGIS

I am using both QGIS 1.8 and 2.0. So either is helpful. A client has given me locations of trial pits but i cannot load them into QGIS no matter how hard i try. For example, 50°24.711 North ...
1
vote
0answers
16 views

Saving/Loading QGIS style .qml and avoid specified symbology

Is it possible to save QGIS styles without the symbology style? This may seem like a strange question, but I am trying to automatically set the ValueMap widget under layer properties via a plugin for ...
0
votes
1answer
28 views

How to delete column/field in PyQGIS?

How to remove or delete column fields in a shape file using python?
1
vote
1answer
20 views

How to calculate regrowth area?

Thanks to Best Landsat-5 TM band combination for detecting fire scars I am able to calculate burnt area in an absolute way (Normalized Burn Ratio). Does a ratio or delta operation exist to calculate ...
0
votes
2answers
2k views

QGis: Merge intersecting polygons into one which are part of the same feature

I'm not a GIS professional so I hope I use the correct wording, at least I hope you understand my question. Let's say there are 5 polygons in the feature A. In the shape file there are more ...
2
votes
2answers
135 views

How do I stop null values from being assigned extreme color values?

I have a raster surface that I kriged in Surfer and imported to Grass GIS but when I view it in QGIS, the null values outside of the interpolated surface take an extreme value and wash out the ...
3
votes
1answer
267 views

How to build a confusion matrix for image classification using SAGA or QGIS?

I did a supervised classification of a Landsat image subset using my training data polygons. I used SAGA GIS for that and everything worked out fine. Now I am stuck since I have no clue how to ...
1
vote
1answer
48 views

How to do a “fuzzy” intersection?

I have two layers that look like this: I want the intersection (or whatever the correct term may be) to look like this where the output polygons are the same as the original base layer, just with ...
1
vote
1answer
21 views

Add XY Column in QGIS [duplicate]

Following on from a previous question of mine, where I was given coords in degree-mins, I have successfully converted them to decimal degrees, thanks for the help. I have created a CSV file from ...
1
vote
0answers
34 views

Some items have coordinates switched when loading PostGIS layers in QGIS

I am having problem with strange coordinates switching when loading PostGIS layers in QGIS. First, I thought, that problem may be cause by the use of GROUP_BY feature in layer query, but later the ...
0
votes
0answers
12 views

How to compute the ls factor equation for USLE model in qgis grass r.mapcalc

To compute the LS factor for the USLE model, the following equation easily works in ArcGIS. How can I perform the same in QGIS under GRASS r.mapcalc? LSfator = Power (("flowaccNW") * ...
1
vote
1answer
115 views

Trying to set NAD 1983 EPSG 102631 in QGIS

I was able to find the right coordinate system online NAD 1983 Alaska But now I don't know what to do. I can't find the coordinate system on QGIS. When I choose the one I think is correct it warps ...
0
votes
1answer
104 views

Merging Raster: ImportError: No module named _gdal_array

When I try to merge rasters I got following error message: _gdal_array = swig_import_helper() File "C:\PROGRA~1\QGISDU~1\apps\Python27\lib\site-packages\osgeo\gdal_array.py", line 18, in ...
3
votes
1answer
61 views

Pulling CSV file directly from website into QGIS?

I want to be able to automatically update my csv files in a QGIS project. My organization has an online database that can easily export csv files. These csv files are constantly updated with new ...
0
votes
0answers
46 views

Raster layer invalid

Im trying to load tiff image using QGis1.8. But Im getting "Layer Not Valid", even though the raster image path is correct. I want to know the reason behind this error. Thanks, suma
3
votes
1answer
126 views

Is it possible to label bar charts?

I have added bar charts to my map and this works fine. But I have no idea how to add values to the bar chart. For example one bar shows the value of 2000 and another shows the value of 2100. Is it ...
1
vote
1answer
183 views

Showing unknown SRS(native srs) on GeoServer when importing shape file into GeoServer

I am facing the problem on unknown srs when I am importing shape file into GeoServer. I am trying to imaport a shape file into GeoServer But when I am publishing the shapefile it giving the Unknown ...
4
votes
1answer
93 views

How to select behind feature which is overlapped with the same layer on QGIS 1.8.0

My issue: I received data which was created without "Avoid intersection of new polygon". There a few overlapped feature with the same layer. I could fine overlapped feature by the spatial query. But ...
0
votes
0answers
16 views

How to perform an attribute-weighted sum of multiple polyline features from a single vector layer?

I have a shapefile of ~8000 polyline vector features representing traffic journeys on road routes. Each has an attribute representing volume of traffic for that journey. The routes are all generated ...
4
votes
2answers
455 views

Are there open source solutions for travel demand modelling?

I'm looking for open source tools for travel demand modelling (eg The four-step UTMS). Preferably in a GIS environment. That works well with Qgis, Grass and Postgis. My question is not related to ...
4
votes
1answer
102 views

Calculating a Unique ID on a Subgroup of Polygons

I would like to assign a unique ID to polygons in a dataset. The catch to my issue is that I would like polygons that fall within a polygon to have the same unique ID. My example is related to ...
1
vote
1answer
39 views

How to write a (memory) layer from QGIS to PostGIS?

I am looking for an "elegant" solution to write, from a python script, a layer from qgis and into a new table of a PostGIS database. I thougth that this might be solved by QgsWriteVectorLayer, but I ...
1
vote
1answer
84 views

What is the best way to display point data (with standard deviation) using QGIS/SAGA/Manifold? [on hold]

I would like to display point data values (indicating biomass at a point) but also to show the standard deviation value for each point. What would be the best method to do this in QGIS (I'm a basic ...
1
vote
0answers
27 views

How to add a TIF raster layer programmatically?

This is my code whenever i try to load .tif image it shows layer is not valid,QgsRasterLayer always return invalid layer (I am using linux 12.04). QString myFileName = ...
1
vote
0answers
22 views

Is it possible to change the default raster style of newly created rasters in QGIS?

If I do calculations on rasters with the raster calculator or other tools, the resulting rasters displayed in my canvas are always in the same default style (singleband gray, black to white...) so ...
1
vote
1answer
18 views

How to select more than one feature using values?

What should I do if I want to select more than one feature using values ? For selecting a single feature, I enter an expression like this which works: "LINK" = 28 Assume LINK as a field in the ...
0
votes
1answer
9 views

QGIS Filters and Querries [duplicate]

In QGIS is there a way to filter a layer using the Query Builder to show all values which include a particular phrase. For example I have a list of organisations and I want to filter all those which ...
0
votes
2answers
86 views

How can I delete dangling paths after merging features

In my previous question I've asked how to can I merge different polygons while converting to GeoJSON and TopoJSON. After a day of researching I've realized that, rather trying to do it command line, ...
4
votes
1answer
246 views

How do I install Orfeo toolbox and Qgis 1.9?

I'm having a lot of trouble getting Orfeo toolbox and Qgis 2.0 working. I followed the qgis wiki instructios, added the ppa, installed qgis 1.9 (it's beautiful, great work!). But when i tried to ...
1
vote
0answers
14 views

r.stream.* commands do not work in qgis environment

I have been working for a while with some grass commands in QGIS environment (r.watershed, r.terraflow, r.thin, r.to.vect etc) with out any problem. I haven't been able to get any results at all from ...
0
votes
1answer
19 views

Apply new style to selected features in QGis

Let's assume that I have selected some features in QGis. Now all the features in that vector layer already has some style applied to it. Now, I want to apply some new style to the selected features. ...
0
votes
0answers
15 views

How to increase the resolution of a 3D image in QGIS GRASS NVIZ

I'm trying to display 3D data in NVIZ within QGIS, but the result appears very low resolution in comparison to the same data in ArcScene. Any ideas as to how to improve the quality would be greatly ...
0
votes
0answers
21 views

How to convert data type from float to integer in QGIS?

Currently I am working on importing data from MSSQL to Qgis 2.4. In imported database table attributes are shown in the format of integer ( in attribute table it showing like 48.23 and 16.20 in ...
4
votes
1answer
3k views

How to do a simple find and replace in QGIS field calculator?

I'm trying to replace selected string values in an attribute table, eg. "Text1" for "Text2" (QGIS 1.8.0), patriculary for those rows with NULL values. I have been trying to use the replace expression ...
2
votes
2answers
587 views

How to convert raster to point in QGIS

I wanted to convert Raster into Point Vector in QGIS. Is it possible? QGIS have option to convert it into polygon but i didn't found any tool to convert it into point. can anyone help me?
0
votes
0answers
88 views

QGIS 2.4: plugin changes map tool canvas click behavior from 2.0

I had created a plugin for QGIS 2.0 to add new features more easily. It involves changing extents and updating snapping options along with triggering the default actionAddFeature(). However, I've ...
1
vote
0answers
12 views

How to group a multiple rasters in MapServer?

I had a map files for each state (raster file) of India. Now I want group all mapfiles to show a single raster or single map file? How I can do in using qgis or any platform?.
1
vote
2answers
318 views

MSSQL Data Not Showing Up in QGIS

I started using QGIS a few weeks ago. I've been able to create some very nice maps with it. I've used the OpenLayers plugins to bring in different basemaps, I've brought in shapefiles and connected ...
1
vote
2answers
278 views

How to create callout/balloon labels in QGIS 2.0?

I'd like to use callout/balloon labels for a vector layer in my GIS using QGIS 2.0. The only way I can see to do this is to position an ordinary label where I want it and then draw an empty text ...
0
votes
2answers
816 views

How to fix ImportError: cannot import name MAXREPEAT on Ubuntu 12.04

I have problem with installing qgis 2.0 on ubuntu 12.04. If I don't install qgis-python plugin then qgis starts normally but I can't access python console in plugins. If I install that plugin then I ...
1
vote
1answer
349 views

QGIS Server does not display test WMS

I'm having a similar problem to this post: Using Qgis server with Ubuntu 12.04 I am using Mint 15 desktop and QGIS 2.0.1. I read the above post and decided to go back a step or two and followed this ...
5
votes
1answer
88 views

Is there a simple way to sort layers alphabetically in QGIS?

I am working on a big GIS project and not being able to sort the items in the Layers panel is giving me hard time. I can have up to 250 layers in the Layers panel. I have a special naming scheme for ...
2
votes
2answers
40 views

Use Values from Raster Statistics (e.g. sum of all cells) in Raster Calculator

I need to do calculations on raster layers which require the sum of all cells of the raster. I've used the zonal statistics tool for that but it gets a little annoying to do those extra steps (run the ...
8
votes
3answers
3k views

How to create polygons with straight lines and right angles in QGIS?

I am running QGIS 1.7.0 on Mac OS X 10.6.8. When creating a polygon, how do I do it so that the lines are straight (90, 0 degrees, etc.) and when I create corners they can be right angles? For ...
0
votes
0answers
13 views

Merge/mosaic categorical rasters in QGIS/GDAL

I am attempting to make yearly bins of some monthly MODIS data for all of the US. The cells of the raster are defined with Julian dates indicating the date at which a burn event took place. After ...