Questions tagged [qgis]

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

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When does a QGIS .qix spatial index of a shapefile need to be re-created?

I understand the basics of spatial indexes but would like to understand when exactly a spatial index would need to be re-created or updated? The reason I ask is because when a folder was moved to a ...
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117 views

Speed execution of PyQGIS algorithms

I don't understand why if I do "manually" some algorithms I get results much faster than when I insert the same in a pyqgis code (with the same input). This happens, for example, with the extract ...
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101 views

Set background or text color depending on expression in an attribute table in QGIS composer

I am using QGIS 3.0.2. I am working on a print composer including an attribute table. I would like to set different colors to each rows, depending on an expression, refering to an attribute. I didn't ...
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671 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 ...
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195 views

Voronoi Polygon Algorithm seems to exclude a Point from processing

I am using the QGIS (2.8.1) Voronoi Polygons Algorithm on a point shapefile. See image below, the red triangles are the points I am using. The resulting polygons miss a part (around HP87). Any ...
5
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2answers
181 views

Automatically moving along columns within a layer as moved to the next item in a QGIS Atlas?

My problem is quite hard to explain, I have attached some images to help illustrate my issue. I want to produce a large number of maps which overlap in geographic area. Currently my data is arranged ...
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161 views

show relations between polygons by highlighting polygons

Is it possible to show relations (for example traffic flow) between polygons (for example counties) by highlighting related polygons by doing a query on a start polygon using QGIS? Here is an ...
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178 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 ...
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481 views

Creating text buffer in legend QGIS 2.18?

I work with this polygon layer and this is my map composer: I used the labels with Text Buffer (yellow and red), and I try to find how I can make the same text buffer in the layer name in the legend. ...
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138 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 ...
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118 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 ...
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102 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 ...
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387 views

What's the fastest way to convert large csvs to point shapefile

I'm working in QGIS, and my current method to change csvs to shapefiles is to import them to QGIS, right click and save as shapefile. For large CSVs (over 100 million rows) it can take quite some time ...
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373 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 ...
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286 views

QGIS doesn't handle PostGis connection resets?

I'm highly frustrated by the fact that if I leave the database alone for a more than a few minutes, I can no longer insert new lines. If I restart QGIS, everything goes back to normal. I believe this ...
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762 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 ...
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461 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 ...
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454 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 ...
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558 views

Setting up PyCharm CE 4 to work with PyQGIS library in Mac OS

I am trying to set up pycharm to work with pyQgis library but with not success till now. I am using PyCharm CE v4 and QGIS version 2.8 I have tried to implemnte the instructions of several posts like ...
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2answers
5k views

WindowsError: [Error 32] The process cannot access the file because it is being used by another process

I am reading images (through Python) and do something. These images are placed in a temporary file, through: tf = tempfile.mkdtemp(filename) I use gdal to read the images (short part of code): ... ...
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0answers
444 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 ...
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0answers
888 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 ...
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1answer
509 views

How to set postgis default sequential value in a QGIS “editable” view?

Introduction In a QGIS project I have a VIEW, that I want to became editable (I'm trying to replicate the versioning system used DB Manager with some tweeks). Therefore I created a few rules to ...
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480 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 ...
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0answers
668 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. ...
5
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1answer
1k views

QGIS GRASS Processing Not Working on MacOS?

Recently upgraded to QGIS3 (3.0.2) for MacOS (High Sierra) and encountered GRASS (7.2.2) issues. Tried adding a custom variable and now when running GRASS algorithms (e.g. r.reclass) I get the ...
5
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2answers
2k views

Publishing QGIS project on GeoServer?

Is there a way to prepare a project on QGIS with many layers and to publish it under WMS service on GeoServer?
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0answers
84 views

Does the projection of a PostGIS table affect the rendering speed in QGIS

I am interested to know whether changing the projection of a PostGIS table will affect the rending speed when viewing it in QGIS. I have two layers coming from QGIS which are exactly the same and ...
4
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1answer
53 views

Calculate distances between consecutive points in QGIS

I have a large dataset containing GPS points of various vehicles that are recorded every 10 seconds. I have added a new id column to these GPS points in order to be able to connect them via the ...
4
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1answer
60 views

Referenced table not found in standalone Python script

I'm trying to run a Python script from OSGeo4W Shell. Im doing this by typing "python-qgis C:\path\test.py" Everything seems to go fine until the script launches the processing module. After that ...
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49 views

Understandiung difference between TIN interpolation methods Linear and Clough-Toucher of QGIS

I started to study TIN in QGIS and created my first TIN from a point layer with elevation. There are two interpolation methods called Linear and Clough-Toucher that give very different results. Linear ...
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25 views

Gdalwarp fails to properly reproject to custom projection

I am trying to reproject my tif file to custom EPSG:3857 projection. Input file picture + gdalinfo: Driver: GTiff/GeoTIFF Files: shd_120arcsec.tif shd_120arcsec.tif.aux.xml Size is 10800, 5100 ...
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53 views

How to calculate the distance between polygons and polygons (or polygons and lines) in QGIS?

I'm new to working with GIS data and QGIS. I'm trying to find an efficient way to measure/calculate the width of streets in a city. I have two datasets: buildings (polygons) and streets (lines). I'm ...
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70 views

Snap geometry/polygon to grid with minimum distortion

I am working on a project to transform polygons given in a pre-defined precision to a lesser precision, which I think is equivalent to snap them to a fixed spacing grid. For example, in the example ...
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46 views

Automatically snap lines at angles when offsetting

I used the geometry generator to offset lines. offset_curve($geometry,"offset") Is there a way to get the lines automatically snapped at angles when they are connected? I can use the rendering ...
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0answers
153 views

Is it possible to rename a table column with an expression in the field calcultor of QGIS?

I want to be able to rename a few column names with an expression in the field calculator in order to be able reproduce this action with the QGIS graphical modeler. I tried to do this with the ...
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0answers
63 views

GIS proj pipeline

I would like to create a custom projection in QGIS 3.10. It is a local stereo and the reprojection between WGS84 and the local stereo uses proj pipeline. For example in cs2cs it is (which works well): ...
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0answers
64 views

Using Geometry by Expression tool to make set of lines in QGIS

I am using QGIS 3.x. I am trying to make a set of lines that are 50m to 2000m, at 50 meter intervals (eg: line 1 is 50m, line 2 is 100m, line 3 is 150m, etc). I did it manually using the Advanced ...
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0answers
66 views

Showing labels as they will be printed/exported in my print layout?

I set up a print layout for a map I want to print in QGIS. Some of my layers have labels on them. When I zoom in and out in the screen, without changing anything else on the print layout, some labels ...
4
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0answers
108 views

Rasterize/Filter with Burn and Weight variables in QGIS

Using QGIS 3.10.1, I am attempting to rasterize some demographic polygons, and then apply a filter (Gaussian) to create a smooth/graduated surface. This works fine for some of my values (e.g. total ...
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0answers
101 views

Styling the legend in QGIS with line layer

Working on QGIS 3.4.13. I have a vector line layer, there are rivers. I put a rule based symbology with two categories and different scale max / min for each category. I want to put style for the ...
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0answers
77 views

QGIS 3: Set custom project variables with input dialog

I am using QGIS 3.10.0 and Windows 10. I have a project where I want the user to define custom project variables. I want to make this user friendly, I don't want the user to need to open the project ...
4
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0answers
73 views

QGIS geometry error:Hole lies outside shell

I am using QGIS 3.8 and I am using a layer from OSM of Tokyo city. The layer is consisted from many polygons and I have tried to merge it but I got error. This is how the original layer was look like:...
4
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1answer
98 views

Points from various sources to one line

I have "unsorted" points from various sources - steming from a hiking track / path. How can I create one line from the closest points (...following the track). I´ve already imported all points to ...
4
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2answers
320 views

Converting raster pixels to polygons with GDAL python

I want to convert raster pixels to vector polygons as below image that is output of "Processing Toolbox--> Vector Creation--> Raster pixels to polygons" in QGIS 3.8: I tried to do this vectorize with ...
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0answers
44 views

Setting default raster statistics extent in QGIS?

I recently found the setting in QGIS to rescale raster symbology using the current extent, which is really handy (Layer styling > Min/Max Value Settings). My question is - can the default extent be ...
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0answers
44 views

Displaying images as part of multiattribute labels using QGIS

I would like to display images referenced in an attribute column as part of a multiattribute label, so that I can eventually print them with the map. I do not want to display geotagged images, since ...
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0answers
226 views

Error using 'Clip raster by mask' in QGIS v3.8.2

I am attempting to clip a raster to a shapefile boundary (country boundary, 1 polygon) using the 'clip raster by mask' tool in QGIS v3.8.2. Both layers are in WGS84, so projection mismatch shouldn't ...
4
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1answer
162 views

MODIS Fire Product tile conversion to GeoTIFF problem

I downloaded a tile (selected tile in the picture) from https://ladsweb.modaps.eosdis.nasa.gov/search/order/3/MOD14--6/2019-08-09/DB/Tile:H25V6 I used gdalinfo on the file. It's output is Driver: ...
4
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0answers
141 views

“Driver not loaded Driver not loaded” when trying to connect to MSSQL database in QGIS 3.8 on MacOS

When trying to create a new MSSQL Connection, I get an error saying: Error opening connection: Driver not loaded Driver not loaded. I have tried both QGIS 3.8.0 and the newest pre-compiled QGIS 3.8.1 ...