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Questions tagged [qgis]

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

7
votes
0answers
382 views

Accessing existing instance of QGIS from stand-alone python script

For my own data analysis pipeline, I am running a split screen setup with iPython notebooks on one side, generating variables from source data, pushing them to a CSV file which QGIS then reads/joins ...
6
votes
0answers
116 views

When using QGIS join by location, how does QGIS determine the first located feature option?

I have used QGIS process 'join attributes by location' in one of the models I have built and I have now been asked to explain in detail exactly how the model is determining the results. I am using it ...
6
votes
0answers
132 views

Processing post-execution script hook to clear scratch layers?

I've been cobbling together some Processing scripts for QGIS 2.18 (I'm not a fan of QGIS 3 scripts), and I keep running into one particular problem: my script creates a lot of scratch layers and they ...
6
votes
0answers
202 views

Point cluster symbology for different categories without overlapping symbols

I'm trying to visualize crimes based on if the crime happened during day or night time. I've tried using the point displacement tool but I'm not satisfied with the results because the readability for ...
6
votes
0answers
1k views

Creating polygon elevation contours?

I'd like to create polygon shapefiles to communicate elevation information on regional maps. I find these draped over a hill shade layer provide one of the best base maps. I can tell some ...
6
votes
0answers
83 views

Show Symbol (e.g. City-Marker) only when an associated label can be displayed

I'm building a map for a certain region with many cities to be displayed. Some of the smaller cities should only be displayed if they don't overlay bigger cities. While the labels of the smaller ...
6
votes
0answers
2k views

Rasterize shapefile using another raster's size and resolution

Rasterizing a vector (shp) I face the following problem: I want my output file (the rasterized vector) to have the same resolution and dimensions as an existing raster. If I understand the interface ...
5
votes
0answers
86 views

Different length measures in QGIS vs. ArcMap

I noticed that QGIS and ArcMap return slightly different length measures when calculating geometries (length) on one and the same shapefile (see image). In QGIS I used the $length command, in ArcMap ...
5
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0answers
72 views

Cumulative value/cost along shortest distance roads in QGIS

I have a road network linking multiple (ca 1830) agricultural production regions to several ports (ca 12). (lines in the pic below are roads, small black dots centroids for producing regions and ...
5
votes
0answers
62 views

Offline editing slides the attribute data over one column and ads an “fid” column

My QGIS 3.4 Madeira project is attached to a PostGIS database (Azure) and looks good. It contains two layers, one with points and one with polylines. Each item in the Pointz layer has about ten ...
5
votes
0answers
109 views

Old .qml style (vector-polygons) from QGIS 2.18 in QGIS 3.4

I have a .qml polygon style file created with QGIS 2.18. It works to import until Version 3.2 without problem. But in 3.4 the style is loaded, but not applied/visualized. The Polygons dissappear ...
5
votes
0answers
616 views

Error running r.thin in QGIS

I get the following error when running r.thin: Traceback (most recent call last): File "C:/PROGRA~4/QGIS3/apps/qgis/./python/plugins\processing\algs\grass7\Grass7Algorithm.py", line 395, in ...
5
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0answers
340 views

Calculating average pixel value for each band across multiple raster layers?

I have a set of raster files that are essentially data sets of precipitation across a region. I have multiple raster files that are the outputs of different climate models. Each pixel in the raster ...
5
votes
0answers
113 views

Render only features located around the the mouse cursor in QGIS?

When hovering over a vector layer in QGIS for feature selection, it would be useful, if only those in a buffer of a certain distance to the mouse cursor are displayed. Any ideas on if/how this might ...
5
votes
0answers
137 views

Value relation autocompletion and dropdown menu in QGIS?

I use a value relation widget which is connected to a list of streets. If I tick "use completer" I can use the autocompletion but the dropdown menu disappear. The dropdown menu appears again only if ...
5
votes
0answers
131 views

When moving a feature in QGIS, is there a way to nudge it rather than use the mouse?

I need to move a lot of features (polygons) in QGIS to fit a newly Georeferenced scanned map that is slightly asymmetrically distorted. This is fine as it is just to provide a print copy. I end up ...
5
votes
0answers
331 views

how to buffer a line with varying distances associated with directional quadrant with open source GIS?

I would like to buffer a set of lines with different distances to the NW, SW, SE, and NE. I have the distances stored in four attribute fields that correspond to the direction the buffer should be ...
5
votes
0answers
120 views

Creating Viewsheds in Graphic Modeler

I am trying to use Graphic Modeler to run viewsheds. As I can’t appear to use the Viewshed Analysis plugin tool in Graphic Modeler and I instead need to use the GRASS command r.viewshed. I am ...
5
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0answers
105 views

Issues with atlas generator and labelling across maps/images

I have a lot of layers in my project and I am trying to use the atlas generator in the print composer to create a tiled map. Some of the layers have labels which have different configurations with ...
5
votes
0answers
538 views

Using QField with Multi-User Access also Offline?

I got 10-20 QGIS-Users which edit all one Project online and offline. Sometimes they do it at the same time. Until now we only used QGisDesktop with a PostGis Database stored in QGIS Cloud(50MB ...
5
votes
0answers
101 views

Preserving Vector Attribute Types When Processing Vectors

Qgis seems to change vector attribute types for certain processes. Is there a way to force preservation of the attribute types? My situation: I have five vector layers I want to merge, all shapefiles,...
5
votes
0answers
267 views

QGIS/Spatialite cluster analysis with density

beginner here I am trying to analyse a large set of points (2 millions) over a set of polygons (3000), and particularly find clusters of points. Doing it in QGIS was taking too long/crashing the ...
5
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0answers
436 views

Computing the slope of a road using DEM

I work with QGIS 2.14 and I want to create a map of road network showing the slope of each road with at least this scale: <3%; 3-5%; 5-7%; 7-9%; >9%. I already have a vector layer of roads and the ...
5
votes
0answers
375 views

What are the considerations for choosing between WKT and WKB geometries?

There are many questions & answers here addressing how to convert between WKT and WKB geometries, and about the specifications or implementation details. But what are the considerations for ...
5
votes
0answers
93 views

Selecting minimum number of neighbouring polygons required to give a fixed total area

I have a polygon layer. I would like to select the minimum number of neighbouring polygons to give a total area greater than a fixed value. In reality the polygons are land parcels and I would like to ...
5
votes
0answers
324 views

QGIS Referencer: Tranformed Failed

I'm using a new install of QGIS 2.18.2 on an iMac running OSX 10.10.5. I create a new project. I use the OpenLayers plugin to show an OSM background of a part of Mayfair in London. I now use the ...
5
votes
0answers
721 views

Build QGIS 2.16.3 on windows 7 SP1 x64

I'm trying to learn how to build QGIS from source perfectly with windows 7 x64 to adapt QGIS for a urban planing. But I get plenty of errors. Until now this is what I'm doing: PART1: VISUAL STUDIO ...
5
votes
0answers
422 views

QGIS Align Rasters how to retain pixel values?

I am attempting to align and then merge a number of rasters of the same resolution and extent, but where the pixels are slightly misaligned (creating small gaps when merged). This works fine using the ...
5
votes
0answers
432 views

Insert sequential row and column values automatically into a fishnet dataset

I have a grid that has about 30 rows with approx 15 columns each. I want to label them as A1,A2,B1,B2 etc (Alphabet row, integer is column). Is there any way to do this programatically? There is no ...
5
votes
0answers
843 views

Is it possible to do parallel processing in GDAL and QGIS?

It seems like processing a large raster dataset in QGIS can cause a crash, for example in QGIS failing to complete clip or intersect and crash dump in qgis. Is it possible to use GDAL parallel ...
5
votes
0answers
82 views

Combine multiple adjoining parts of a single feature

In QGIS, one polygon feature resulted from merger of several adjacent polygons. This one new polygon feature has a single line through it that I would like to eliminate. When hovering over individual ...
5
votes
0answers
778 views

How to digitize in stream mode in QGIS, using a tablet?

How to digitize in stream mode in Qgis, using a wacom cintiq tablet? freehand it's no use. i need something like MNDR stream digitizing extension for arcview 3.x, which allows continuous tracing, ...
5
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0answers
433 views

Is there a tool that shows dimensions during editing?

Is there a plugin or tool providing following functionality: I select 2 points (or vertices) - it shows the length between this points When i edit the point (or move vertex) the length automatically ...
5
votes
0answers
231 views

How to calculate radius of curves in a polyline with QGIS?

I have a polyline made of curves and I would like to know if there is a way in QGIS to calculate the radius of the curves?
5
votes
0answers
864 views

Print Composer Template produces empty map?

I have a print composer template which I'm trying to populate with different subset queries from a CSV-derived vector layer using the Python API. However, all the output PDFs contain everything except ...
5
votes
0answers
1k views

QGIS cannot open output layers

I have problem with QGIS 2.0.1. Everytime I run tool from SAGA or GRASS, I get exactly the same error, for example: Oooops! The following output layers could not be open Channel Network: /tmp/...
5
votes
0answers
387 views

Can extracting raster values work in polygons' CRS without raster resampling?

I am trying to extract raster values using polygon layer with different CRS. Raster is in WGS84 (EPSG:4326) and the polygons in UTM (EPSG:23031). 1. If I want to work in the projection of the ...
5
votes
0answers
650 views

How to debug Quantum GIS PlugIn Visual Studio DLL?

I have developed a Quantum GIS plugin layer using Microsoft Visual studio and placed it in my plugins folder of my customized QGIS application. I now intend to debug the DLL using Microsoft Studio. ...
4
votes
0answers
47 views

Snap LineStrings considering direction in QGIS 3

I have 2 projected shape files: Roads (red) and public transit routes (blue): I want to snap the PT routes to the roads, but because of inaccurate marks sometimes the routes are snapped to the wrong ...
4
votes
0answers
42 views

Referencing an output in an expression in process modeler

In the process modeler, I'd like to reference an output of a previous step as one of the parameters of an algorithm. In this case, the previous step was clipping a large raster and I want to use the ...
4
votes
0answers
59 views

Using Layer Parameter variables in Field Calculator within QGIS Model?

If I define a Vector Layer as an input parameter to a QGIS model, then the parameter name is exposed as a variable in a Field Calculator within the model, however I am unable to use this variable as I ...
4
votes
0answers
56 views

Creating a segment for fixing water pipes and finding disconnected areas

I'm wondering if there is a tool for this problem. I'm using QGIS 2.14.2. Basically I want to select a pipe and find closest valves there is and to turn them off. After that I need to find all pipes ...
4
votes
0answers
289 views

Running OTB Random Forest Classification

I am having trouble processing a satellite image using the RF (Random Forest) classification, that is a machine learning algorithm in the Orfeo Toolbox of QGis 2.18.1. When I run the Tool, the ...
4
votes
0answers
225 views

Add private plugin repository to QGIS 3.4

I want to add a repository to my QGIS 3.4 which is on a private server. The repository contains all files needed (plugin.xml and metadata.txt for example) and has the structure as described here: Is ...
4
votes
0answers
337 views

QGIS 3.4.1 Extensions Repository not available

In my QGIS 3.4.1 installation (Windows 10) the extensions repository says "unavailable", like in this older post: Why I can't install plugins?. I already added the repository with "HTTP" instead of "...
4
votes
0answers
87 views

Setting grid in QGIS that automatically adjust its intervals?

I am setting a template for multiple maps in QGIS 3 Layout and i was wondering if there is a way of automatically adjusting the grid's interval as a function of the scale of the map? I did a bit of ...
4
votes
0answers
146 views

Question marks (“?”) in QGIS layer panel when using svg markers defined with “Data defined override”

When using svg marker symbols and set the path to svg file via Data defined override the svgs display well in the map canvas, but not in the layers panel (applies for QGIS 2.x and 3.x). svg marker ...
4
votes
0answers
201 views

How to use a WCS layer in QGIS for processing?

I have a GeoServer serving raster dem data out via WCS and can add the layer easily to QGIS (3.2) but when I try to use it as the input for an operation (e.g. HillShade) I get an error. Processing ...
4
votes
0answers
118 views

Offline editing solution for small GIS project with multiple editors?

I have a specific use-case that I cannot seem to find any solutions for online, so any and all advice would be most welcome. Some basic details: I am part of a small academic organization (a research ...
4
votes
0answers
64 views

Equal length dashed lines while using 'segments_to_lines' in QGIS

I want to create tapered lines with a dashed line stroke (to style intermittent streams). I followed this tutorial to create the taperered lines, basically using Geometry generator with the expression ...