Questions tagged [qgis-3]

for questions specific to the 3.x series of QGIS.

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setDataSource() not working with query PyQGIS 3

uri = QgsDataSourceUri() uri.setConnection(aHost=self.db_conn.host, aPort=str(self.db_conn.port), aDatabase=self.db_conn.database, aUsername=self.db_conn.user, aPassword=self.db_conn.password) ...
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  • 151
1 vote
0 answers
25 views

Get coordinates from a second layer

I'm using QGIS 3.16. I have to get coordinates from a line-layer (layer_1) and write them to a point-layer (layer_2). I cannot create the coordinates in layer_1 because i am not allowed to create any ...
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  • 11
1 vote
0 answers
16 views

Authentication problem PostGIS - QGIS

I am using PostGIS as the main data storage for QGIS with stored login credentials. This works great, with one exception: For some layers, QGIS starts asking me for login credentials to the QGIS ...
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14 views

Alternative to PointsToPath in QGIS 3 to link point geometries based on integers (ranking, dates etc.)

I am looking for a QGIS 3 alternative to the QGIS 2 plug-in PointsToPath, which allowed the linking of points based on an order provided in a simple integer column. I would like to create simple maps ...
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0 votes
0 answers
13 views

Using Processing Algorithm script QGIS3 outside GUI [duplicate]

I get an error when I try to use a Python script using processing algorithms. If I use the following script, the program will encounter an error. So there is no processing. import processing ...
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1 vote
0 answers
15 views

Labelling / symbolizing layers using QGIS [closed]

I'm realizing the same analysis on specific layers on QGIS. I need to display a specific information (like showing code "xxx", then "yyy", then "zzz" etc.) and export ...
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  • 119
-2 votes
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20 views

Failing to clip a line to a polygon (river to Catchment area) [closed]

Could not create layer D:/Educational/Anslow/Rur_river.shp: Creation of data source failed (OGR error: D:/Educational/Anslow/Rur_river.shp is not a directory.) Execution failed after 0.28 seconds
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1 vote
0 answers
39 views

Taking vertices and using point to path creates a mess, how can I snap the lines to roads?

I’ve tried points to path (and various other processing tools) however I end up with this: When really it should look more like this line string (without the gaps separating chunks of road here and ...
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0 votes
0 answers
29 views

Create reference number based on direction of line

I'm looking to label a series of lines based on a direction of the trail rather than any cardinal direction (east to west, north to south, etc.) in QGIS 3.4 for Windows 11. For example, let's say I ...
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3 votes
1 answer
71 views

Changing symbol by expression in QGIS [duplicate]

The same way we can define the color of symbols using expressions, do you know if we can change the symbol itself in QGIS 3.24? In my situation, I use a layer 'OPTIONS' to change values on the map, ...
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  • 119
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36 views

Using QGIS processing algorithms in C++

There are no instructions for using QGIS processing algorithms in the C ++ programming language but it exists in the Python language. Is it possible to use QGIS processing algorithms in C ++?
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18 views

Get single feature's style properties in PyQgis

Im creating a script to export kmz files from shapefiles using a PyQgis script. I already coded the exporting part and its working, but now I want to, for each feature, get their color, line thickness ...
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  • 343
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0 answers
19 views

Separately adjusting opacity for each polygon in feature using PyQGIS [closed]

I have a feature with about 5000 polygons. I'd like to adjust the opacity of each feature based on a column in the attributes table. I've experimented with buffer_loc but I think my problem is just ...
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1 vote
1 answer
73 views

Adding "Draw on canvas" option for the input box of Qgis Graphical Modeler

I have a very simple model created in Qgis Graphical Modeler. It takes polygon vector data as input and generates random points inside. What I want is to add an option to introduce input data using &...
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  • 107
2 votes
2 answers
74 views

QGIS : EPSG4326 : arc of circle with X radius centred in Z (aviation)

I am trying to make a polygon from the aviation LPPO FIR (Santa Maria Oceanic Flight Information Region), that some portion is described as "arc of circle with 100NM radius centred at PST NDB (...
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  • 23
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0 answers
30 views

QGIS desktop windows lacking annotation tool

I am fairly new to QGIS. I created a QGIS project with a country map and some annotations on it. When I open it in QGIS I cannot see the annotation tool option on the toolbar. I need to edit the ...
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3 votes
1 answer
39 views

PYQGIS MapLayerComboBox filter on both layer type and field within layer

I have created a plugin, initially for myself (so I didn't have to worry about error handling), but now I need to hand it over to my colleagues and I need to make it fool-proof. I have already ...
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  • 127
0 votes
0 answers
12 views

How to Import Win32api in QGIS 3.14?

I have QGIS Version 3.10 (python version 3.6) in My code i used the win32api module its working fine. but same module while importing in QGIS 3.14 its giving Error ImportError: DLL load failed: The ...
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1 vote
0 answers
33 views

New field and joined fields not displaying in attribute table field dropdown in QGIS [closed]

I joined some fields to a layer and also added a new field. These fields display as expected in the layer's attribute table. Now I want to create an expression for one of the new fields but it doesn't ...
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  • 19
2 votes
1 answer
94 views

Plotting two sets of XY coordinates from same vector import file

I have written a QGIS plugin that creates a .CSV file and imports it into QGIS. In it there are two pairs of XY data in columns. I have the script to import the .CSV as a layer and specify one of ...
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  • 127
2 votes
0 answers
30 views

In QGIS 3.x for Windows, is it possible to add more files to the Project > Open Recent menu?

Running QGIS 3.16 in Window 10. Right now, my "Project > Open Recent" menu shows a list of the last 19 .qgs/.qgz files I've opened. I'd like to increment the number of recently opened ...
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0 votes
0 answers
22 views

Plug-in to reshape sharp edges to circular string is not working near to start/end point of polygon

I am developing a plug-in in QGIS. By using two points I am creating a circular string to reshape sharp polygon edges to round. The plugin is reshaping 3 edges perfectly but failing reshaping near ...
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2 votes
1 answer
49 views

Adding PostGIS mixed-geometry layers in standalone QGIS scripts the same way as QGIS GUI?

I am trying to use PyQGIS to load PostGIS layers into QGIS 3 using the code below: from qgis.core import QgsProject, QgsVectorLayer, QgsDataSourceUri, QgsApplication #init Qgis QgsApplication....
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0 answers
28 views

Error Qt QTemporaryDir when starting QGIS 3.25

After opening QGIS 3.25 appears a message on the top: 1-Qt: QTemporaryDir: Unable to remove "C:\Users\User\AppData\Local\Temp\QGIS3-aPRVXc" most likely due to the presence of read-only files....
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  • 119
2 votes
1 answer
47 views

Converting QGIS feature selection into dataframe to allow plotting

I have a layer containing thousands of points of X,Y,Z data (sample below). fid field_1 field_2 field_3 1 525146 675224 -342.1 2 525148 675224 -342.2 3 525150 675224 -342.1 4 525152 ...
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  • 127
0 votes
0 answers
16 views

How do I know if the marker symbol layer will be displayed during rendering?

One of the layers of my marker symbol is displayed only when the data-defined override condition is met. Here is the code in which I get the layers of my marker. I need to find out whether or not this ...
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1 vote
0 answers
12 views

An error occurred while LULC raster converting into Vector in QGIS 3.16

The error depicts above come again and again while converting land cover classification raster into vector shapefile in QGIS. In semi automatic classification plugin, there is an option to check ...
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  • 11
0 votes
1 answer
35 views

Using the closest Point feature to a line features start and end point [closed]

I have points across my plan and I have connected them with a line feature. Now, I want to use the names of the points closest to the start and end of the line to be added to the line features ...
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3 votes
2 answers
89 views

Extract Single (or small number) Contour from DTM data in QGIS

I understand that Contour data can be extracted at particular intervals fairly easily, but have been recently mapping a number of Flood Water Design levels which are denoted to the nearest 0.001m. It ...
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  • 187
1 vote
0 answers
45 views

Speed comparisons when querying large datasets: ArcGIS Pro, ArcMap, QGIS [closed]

I recently needed to query tax parcels for a list of parcels within a single town, using IN(…) on a list of tax IDs for the parcels I needed. I ran the query on both the public tax parcels, which ...
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  • 167
0 votes
1 answer
26 views

Split with Lines not splitting polygon in QGIS [closed]

Split with Lines does not appear to be working for me in QGIS 3.24. My line and polygon are in the same CRS, you can see that they completely intersect but when I get the results, the polygon is ...
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0 votes
0 answers
24 views

QGIS 3.24 - how to export points as arc or polygon

I have a GPS coordinate file that defines points (locations.) I have a second application that is limited in that it can only show arc or polygon shapefiles. This application can't process a point ...
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  • 1
0 votes
0 answers
30 views

30m SRTM DEM is displacing incorrectly with coordinate range error in QGIS

I am trying to import DEM data to QGIS. Firstly, I have downloaded it from https://dwtkns.com/srtm30m/. For instance, I have N35E117 here in QGIS with corner coordinates: Corner Coordinates: Upper ...
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3 votes
2 answers
44 views

Navigating attributes tables with arrows keys in QGIS

In QGIS 3.24.1 I am trying to navigate through attributes quickly using the arrows keys on the keyboard, as I was doing on previous versions. Unfortunately, QGIS is trying to make the number in the ...
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  • 31
0 votes
1 answer
37 views

Pixel size convert from degrees to meters of Martian DEM

I have a Martian DEM whose pixel size is specified in degrees instead of meters. I was trying to convert in Global Mapper but it didn't work. Now I am trying convert in QGIS with projections but it ...
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  • 1
3 votes
1 answer
102 views

PyQT progress bar freezing

I create a progress bar using the code below on the Qgis console. However, the bar freezes in the beginning, doesn't increase at all, and suddenly appears as 100% in the end. What could be the reason ...
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  • 107
3 votes
1 answer
55 views

Avoiding QGIS plugin window to open at start

I have written a few QGIS plugins based on dockwidget (Spectre Viewer and Stripchart viewer). When opened, the plugin window is expected to stay open and react to interactions with opened layers. This ...
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  • 2,777
1 vote
1 answer
34 views

Adding wkt.csv file to QGIS 3 project using script

I have written a plugin using the Plugin_Builder tool. It takes a CSV, rearranges it and adds a column of WKT coordinates in the style LINESTRING(x1 y1,x2 y2). It then writes it as a new .csv. This ...
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  • 127
1 vote
1 answer
48 views

Keeping track of features when adding them to new layer using PyQGIS

In my plugin I iterate through 8 different line layers and add only certain lines to a list. This list I add to a new vector layer because these lines are the only ones I care about. However, I need ...
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  • 151
0 votes
1 answer
14 views

QWC2 does not display my map layers on host machine

I have been trying to set up my project following this documentation: https://github.com/qgis/qwc2-demo-app/blob/master/doc/QWC2_Documentation.md but I can't get my layers to appear on the map, only ...
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3 votes
1 answer
78 views

Loading QLR file in QGIS using PyQGIS

I'm trying to load a qlr-file in QGIS 3.16 and zoom to a certain area using python: QgsLayerDefinition.loadLayerDefinition('E:/QGIS/test.qlr',QgsProject.instance(), QgsProject.instance().layerTreeRoot(...
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  • 31
0 votes
2 answers
40 views

Substituting label using QGIS

I want to modify my labels "CA Vex Eté Mé (Cou)" with the substitution option (my qgis version is 3.22) I don't understand why for this label it doesn't work. Is it related to parentheses ...
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  • 601
0 votes
0 answers
38 views

QGIS - Very slow map rendering and WMS timeout

I am working on a powerful desktop, it was custom made so I do not know the exact specs however ram is 64gb and it was made for 3d modeling. I am finding QGIS 3.22.2 to be very slow when rendering ...
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  • 1
0 votes
0 answers
21 views

Georeferencing with gdal_translate and gdalwarp fails

I have been struggling with the georeference plugin in QGIS 3.24 Tisler in Ubuntu (and also in Windows, although it doesn't crash on the latter); first I thought it was my dataset but then tried to ...
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  • 3,269
1 vote
1 answer
43 views

AutoFields Plugin for QGIS 3? Or best way to set up Default Values via PyQGIS?

I am working on transitioning my workflow from QGIS 2 to QGIS 3. I was using the AutoFields plugin in QGIS 2 to setup automatic adjustments to the attributes for lines and points (namely their length, ...
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  • 315
3 votes
1 answer
50 views

Creating lines indicating the shortest distance points to line in QGIS [duplicate]

How can I create lines indicating the shortest distance from a points dataset to a to line, avoiding the line to points tool first? In the past (at another company) we used MapInfo "Distance ...
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0 votes
0 answers
16 views

QGIS: Converting Rasters (Bathyemtric ASCII & TIFF) to polygon

Currently using QGIS 3.16. I essentially want to create a shape file polygon for the extents of bathymetric grids I am currently working with. The grids are high resolution (2m,5m,10m) and come in a ...
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0 votes
1 answer
30 views

PyQGIS 3 Select features by mouse click not working

I'm using the solution provided in this question. but when I click on the canvas nothing happens. here is my code from qgis.gui import QgsMapToolIdentifyFeature, QgsMapToolIdentify from qgis.core ...
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  • 151
0 votes
0 answers
18 views

Extract query parameter from QGIS print request URL

I would like to extract a query parameter in a print request in a Qgis-Layout. But I did not find a way to do so (or any similar example). Let's say I have following URL: http://localhost/qgis/...
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0 votes
0 answers
19 views

QGIS native:rasterize alg won't create alpha band

I'm running the rasterize tool against a .png tilemap layer. The manual "export raster" option exports a 4 band .tif as expected, including an alpha channel. However, when I implement this ...
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