Tagged Questions

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

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1
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0answers
25 views

QGIS - Auto-Update Color-Ramp to Current Display Extent

When displaying raster files in Qgis with the color-ramp stretched to the min/max values of the current display extent, the min/max values don't update automatically when zooming or panning to a new ...
0
votes
1answer
39 views

Is it possible to create one raster elevation layer from two different point layers in QGIS?

I have two layers with X,Y,Z data. The data overlay only partly. Is it possible to create one raster layer with elevation data using the 2 sets of data but without merging them first?
2
votes
0answers
60 views

best method for gridding or interpolating elevation data

I wonder if someone can recommend the best method for gridding elevation data in QGIS, GRASS or similar. The elevation data I have is collected along 1m spaced lines at approximately 1 reading per ...
3
votes
0answers
38 views

Is there a limitation on the numbers of layers that can be displayed in QGIS?

I have been looking for an answer to this question for the last several weeks, so hope that someone here has encountered the same issue and has a viable solution to my problem. I am currently using ...
4
votes
2answers
80 views

How to programmatically delete all inner rings of a polygon layer?

I have many polygon layers, each layer containing many polygons with inner rings. I know that you can delete a ring manually with QGis (Edit -> Delete ring). I need the python equivalent to ...
0
votes
0answers
27 views

What is causing this QGIS processing model to fail at r.mapcalculator

I can't figure this out. I can run a number of tools from the processing toolbox separately with success but when I string them together in a model it keeps failing (image of log below). It looks ...
3
votes
0answers
43 views

Where to find comprehensive descriptions of tools in QGIS, SAGA, Orfeo, etc. toolboxes? [closed]

There exists a large number of tools for QGIS (e.g. SAGA, GRASS, ORFEO etc.) - however none of these have sound description of the aim of the tool, the algorithm itself, differences to other similar ...
1
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1answer
52 views

QGIS Metatools error

I haven't been able to successfully use the QGIS MetaTools plugin for describing metadata. Has anyone used it before? When I try to create metadata for a shapefile, the plugin creates the xml file but ...
3
votes
1answer
95 views

How to calculate the intersected area from a layer with overlapping buffers in qgis

I need to calculate the area of landusetypes in 50m around various dots (all in one shapfile). My problem is, the buffers around the dots are overlapping each over in some places. I tried to ...
2
votes
2answers
66 views

Is there any way to 'clean' up ASTER v2 DEM data?

I downloaded all the tiles I needed, then plotted them to find that they don't all seem to have the same quality. Basically, you can see all the edges of a lot of the tiles. Is there any way to clean ...
2
votes
1answer
76 views

Layer with custom UI not working properly

I have a problem with QGIS 2.4 when introducing layers with a custom UI. More precisely, widgets such as CheckBoxes are not recognised as such (appear as Text Edit in Attributes) and the corresponding ...
1
vote
1answer
64 views

Syntax to add attributes in a line in the Expression String Builder

I have several columns with certain values, here's an example: | Apple | Banana| Orange | Pear | Expected result | 1 | 1 | 1 | 1 | red | 1 | 2 | 2 | 1 ...
1
vote
1answer
43 views

Rotating geometry to specific angle using pyqgis?

I do not know how to rotate a geometry using pyqgis. Is there any sample/example code available to show me how?
3
votes
0answers
62 views

Problem with performance when loading PostGIS layer using pyQGIS

I'm having a question on loading a PostGIS layer into the project from my QGIS plugin. The code is like this: uri1 = qgis.core.QgsDataSourceURI() uri1.setConnection(str(host), str(port), ...
1
vote
2answers
68 views

Export long lat from polyline as csv file in QGIS

I want to draw a line in QGIS and then, export the long-lat of each point into a Comma Separated Value (csv) file. I tried doing this by creating a new shapefile layer and then using the Add Feature ...
2
votes
0answers
54 views

CRS problem: not recognizing the CRS of shapefiles to be the same for all

I'm attempting to aggregate (average) the attributes a point layer to polygon attributes (i.e. block groups and counties) via a spatial join. Both the points and polygons are in the same projection - ...
2
votes
2answers
42 views

How to get for a given pixel the values from different overlapped rasters?

I have a few rasters representing different soil properties, like soil pH and sand content. The rasters overlap perfectly, have the same dimensions and same coordinate reference system. I would like ...
1
vote
0answers
36 views

QGIS equivalent to ArcMap Aggregate Polygons

I am looking for a tool in QGIS 2.40 that performs the function ArcMap refers to as Aggregate Polygons. Does anyone know if this functionality (or anything similar) exists within QGIS currently? ...
2
votes
1answer
52 views

How set correct options for displaying a grid in QGIS composer?

I am using q. 2.5 4291337 in Windows 7 64 bits. I am working with raster and vector layers in EPSG 26714 (UTM NAD27 14N). In this version of QGIS, you are able to put a grid in a different CRS of the ...
2
votes
1answer
110 views

Possible to set an attribute field to update automatically based on another field?

If I have 2 attribute columns and I wish to change certain values, is it possible for the second attribute column to automatically update its values based on an expression? Example: Age | Status 10 ...
1
vote
1answer
46 views

Import shapefile into GRASS in QGIS

I am using the GRASS interface in QGIS 2.4. I have successfully imported my shapefiles into GRASS using v.in.ogr, but when I try to then use a GRASS tool, like v.net Network maintenance, the select ...
2
votes
0answers
84 views

Remove pseudo nodes in QGIS

I have a shapefile of city streets. I tried to run the Road Graph tool on them but the select box does not populate with the layer. I ran the Topology Checker on the layer and found that there are ...
2
votes
0answers
81 views

Failing to merge rasters in QGIS

I am new to QGIS but have some familiarity with other GIS software (namely ArcGIS). I want to merge a number of LiDAR digital elevation model (DEM) tiles (specifically, 30 individual tiles) to ...
2
votes
0answers
38 views

How I can create a raster and have the same overlay as another raster in QGIS 2.4?

I have made a graphical model in QGIS 2.4. I have to create a raster equation to rasterize a polygon shapefile. I want to rasterize my shapefile and I want to ensure that this new raster will ...
0
votes
1answer
58 views

OpenStreetView or points from CSV but not both showing?

I'm using QGIS on Mac (most recent version) and am trying to map coordinates from a csv file. When I import the file normally without having any base map, the coordinates how up distributed like I ...
2
votes
2answers
57 views

How do you make an unclassed choropleth in QGIS 2.x?

How do you make an unclassed choropleth in QGIS 2.x? I'm using 2.4 and can't find an option in a layer's Style tab like the continuous color option that seems to have existed in QGIS 1.x. I'm curious ...
1
vote
0answers
222 views

Ubuntu 14.04 Another ImportError: No module named qgis.core

Issue I feel like this is covered territory here, but the issue is has appeared on two separate occasions for me--first when upgrading from Ubuntu 12.04 to 14.04 in May. I got it fixed then, but I ...
3
votes
1answer
95 views

What is the status of any ongoing efforts that will allow QGIS to display .las files directly in the main 2D window?

After some research on QGIS's ability to display .las files, I came to the conclusion that it is not possible: currently any attempt at this requires converting .las to .shp as described here and ...
1
vote
1answer
33 views

Point input for polyline not acceptable?

Input QgsPoint(s) are returning an error in a Polyline creation routine. Any clues?! processing.runandload("qgis:polygoncentroids", Base, "memory:CenterNode") ...
4
votes
2answers
79 views

QGIS renders outlines where none should be

QGIS always renders the borders of a feature polygon. How can I disable this? Even if I set Border style to "No Pen" and the colour is exactly the same for different categories there is a small grey ...
0
votes
1answer
113 views

QGIS Processing error with SAGA, “output layer could not be open”

QGIS 2.4.0 SAGA GIS 2.0.8 DESCRIPTION ERROR when processing with SAGA. I used the "Shapes to Grid" function. The error given: "Oooops! The following output layers could not be open". This error ...
1
vote
1answer
43 views

Where is the log for advanced Python calculator errors?

There is a specific log file for Advanced Python calculator in QGIS 2.4.0? I got the tab message below point to a log file there I wasn't able to find by myself.
2
votes
1answer
186 views

How to create contour lines from point data?

I'm using QGIS 2.4.0 and I have a shapefile of points with elevation data and X and Y coordinates. I'm using windows 7 OS. The idea is to create a contour line SHP using my point data. My question ...
4
votes
2answers
88 views

Wrong $area from field calculator (QGIS)

The area of the polygons in a layer, calculated by the field calculator with "$area" is wrong (much too big) for some polygons. If I draw the concerned polygon again, the area is calculated correctly. ...
2
votes
1answer
127 views

How to create a catchment from a point using a DTM raster in QGIS?

I need to find a better way to delineate a catchment from a given point on a watercourse using a DTM - currently I am either using FEH, or if the catchment is too small using contours to draw ...
3
votes
1answer
46 views

Automatically create Text/HTML annotations in QGIS on a Point Layer

How would one proceed to generate an HTML annotation or a Text annotation for all points in a shapefile? They are all points. What I want to do is load up a shapefile containing coordinates and values ...
2
votes
1answer
44 views

Cannot toggle ''edit'' of shapefile in QuantumGIS 1.8

My problem is as follows: I imported a number of shapefiles from a .gpx-file from a gps-device. Each shapefile contains a number of waypoints. For the study I am doing, I need to give all of them ...
2
votes
1answer
49 views

Clusters of points: Determining the centroid (QGIS)

I've basically got the same issue as this post, but can't find a way to transplant the ArcGIS solution to QGIS. I have household-level geo data for 10 villages spread out across the country. I need ...
2
votes
1answer
119 views

Looking for QGIS 2.4 C++ Hello World example?

In the project I'm working on (C/C++/Qt application), we are trying to integrate QGIS (latest version desirable, 2.4 for the moment). But there is very little information in the web on how to use QGIS ...
2
votes
0answers
40 views

QGIS how to make unedited data?

I have a table in QGIS (using QGIS 2.4). I have created a form for adding attributes. When I add new objects on the layer, I also create it's attributes. Can I make attributes that I have added ...
1
vote
0answers
25 views

Distorted exported georeferenced tif from far north

I'm trying to export a tif file for R, to plot my data on top of. I have geo-referenced this tiff file: "background_changed" from "Background". But when i export it, the file is very compressed in ...
1
vote
0answers
45 views

How to load style from postgresql?

Is there any way to load a postgresql style for a vector layer using python? There is a function: loadNamedStyleFromDb (const QString &db, const QString &theURI, QString &qml).Does it ...
3
votes
2answers
104 views

Why are there no line breaks in my labels even though I added \n?

I'm having an issue with creating multi-line labels in QGIS. I believe I have the syntax right in the label expression because the output preview looks correct. However, on the map, everything ...
1
vote
0answers
33 views

How to do LOS Analysis in QGIS?

I am not able to do LOS analysis in QGIS. I have point Features and Raster SRTM Data. I have installed the LOS Plugin in QGIS but not getting any results. Kindly suggest?
2
votes
1answer
37 views

Using TIN - interpolation plugin - to calculate volume

I am having trouble calculating the volume of my TIN. I have attempted to create a TIN using the interpolation plugin in QGIS. Here are the steps that I followed. I added a Zvariable row in the ...
2
votes
1answer
37 views

How to change parameters of certain algorithms in QGIS process modeler during run time?

I am using Process modeler to automate a bunch of things like Create Graticule -> Extract points at the graticule centeroids -> Add coordinates to the points -> update certain fields of the point file ...
3
votes
4answers
342 views

How to fix quickly a lot of geometry validity errors in QGIS?

I am working on ownership data at a US county level. I have one shapefile per county that contains thousands of tax parcels. I need to dissolve the polygons representing parcels owned by the same ...
3
votes
3answers
88 views

USA County level, detailed OpenStreetMap basemap in tiff?

Is there any way to get detailed (close zoom) OSM tiffs at the county level in the USA? I would like to use them as basemaps for a class I am teaching in GIS, using QGIS. I know about (and love) the ...
1
vote
0answers
45 views

Word cloud labels in QGIS from database

I would like to do some word clouding as labels in QGIS from a series of tables in a database. Examples of word clouds can be found here: Word Cloud - Google Search I have two tables in a database: ...
-1
votes
1answer
33 views

How to clip a raster with a mask in QGIS? [duplicate]

I am trying to clip a raster using a virtual raster as mask layer in QGIS. It doesn't create a file. Could anyone explain how I should proceed to do that?