Questions tagged [qgis-3]

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

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2
votes
0answers
22 views

Tools for fixing geometry of shapefiles

does someone have experience in fixing geometry errors in QGIS 3.10 LTR? I'd like to fix geometries first and then use processing algorithm "Snap geometries to layer". So far, the algorithm ...
2
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1answer
31 views

PyQGIS - Processing.runAndLoadResults(“qgis:mergevectorlayers”) throwing vague error, occasionally works

I am trying to convert all the text files in a directory (CSV files that contain xy points with additional fields of associated data) into a single merged shapefile. Then create a line shapefile from ...
1
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1answer
36 views

QGIS average/mean Z-value of polygon

I am trying to derive an average/mean Z-value of the GPS measured polygons. The standard z($geometry) I use for point layers doesn't work obviously. I could use z(start_point($geometry)), but that is ...
1
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0answers
75 views

Can you regularize building footprints in QGIS like you do in ArcGIS?

I'm using LiDAR data where I've extracted the "building" category and created a raster dataset. I've then 'polygonized' the raster to create a vector polygon shapefile of building fooptrints....
3
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1answer
60 views

Splitting string into “alphabetic” or “numeric” in QGIS 3.10.1

What are the right functions and formulas with the field calculator to delete "alphabet" or "number" inside a field? Let me be clear. I want to be able to delete "alphabetic ...
0
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0answers
27 views

Select connected lines from a starting point

I have a layer representing Watermain's made up of 2D lines. All the lines should be connected at the end points, but there are often very small gaps between them. Dead ends are connected at only one ...
2
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1answer
43 views

How to keep 0 decimals using QGIS Field Calculator's “to_string”

Why does Field Calculator's to_string function rounds decimal numbers if they have zeros? For example: to_string(70.0) gives 70 (textual). But I would need it to be 70.0. And as I have to convert an ...
1
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1answer
80 views

Discrepancies in reading geopackages between ArcMap and ArcGIS Pro

I have a GeoPackage database with a few layers inside of it. One layer, which has about 1000 records, some complex geometry, but no relationships, would not open correctly in ArcMap (specifically ...
1
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1answer
45 views

Using SVG symbols in QGIS 3 that are not saved locally

I am trying to design a QGIS (3.10.7) project which would enable users to work from home and not bind them to a specific computer at their workplace. I am using the PostgreSQL/PostGIS database to save ...
0
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0answers
33 views

Changing SVG marker color using Expression String Builder

What is the proper way to use the Expression String Builder to set a specific color for an SVG symbol? I found some geology svg symbols through this StackExchange answer that I had been looking for ...
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0answers
22 views

QgsRasterBandStats returns nan for mean and sum of squares in QGIS3.4

I have a problem with certain raster files in QGIS 3.4. When requesting statistics via QgsRasterBandStats the average, the sum returns nan. The other statistics minimum, maximum, sum of squares and ...
1
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0answers
39 views

How do I stop QGIS from crashing when trying to create a DEM from a contour line file?

I am trying to use the same methodology I have used in the past to create a DEM from a line shapefile containing contours. However, it keeps crashing when I follow this methodology. (Using QGIS 3.10.9 ...
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0answers
38 views

Alter Rectangle Polygon by Keyboard to Have Specified Dimensions (eg 1km x 1km)

Here is my current workflow. Press "New Shapefile Layer" with "Geometry type": "Polygon" Press "Toggle Editing" Press "Add Rectangle from Center and a ...
0
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0answers
50 views

Enable the current location panel in QField

How can the current location pannel be enabled within QField? (see picture below)
3
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2answers
63 views

When using case when in QGIS 3, even without else, all other previously filled cells are replaced by NULL

I would like to update a column with different strings based on other strings in another column. For instance : if A, B, C in column 1, write Cat1 in column 2. So I use "case when". But even ...
3
votes
1answer
34 views

Creating value in QGIS based on multiple “OR”-conditions

Different cities are part of the same subregional group. I would like to assign this same name to all these cities. I want to live the other cells empty. So far I have tried these but it doesn't work: ...
1
vote
1answer
29 views

QGIS 3.10: attribute form showing foreign key instead of referencing field

In a QGIS 3.10 project, I've set up a relationship between two postgis table. In postgis, table A has two unique fields: "id" and "name". "Id" is the primary key but &...
2
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0answers
54 views

Database compatibility between QGIS and ArcMap [closed]

I'm picking up ArcMap having started off in QGIS. I've been struggling for a while now to make databases that both QGIS 3.10 and ArcMap 10.7 can read and write. It seems ArcMap imposes much stricter ...
3
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1answer
63 views

QGIS 3.10 - Changing display name of layer

Is there a way to change display name of layer without changing layer name ? The field 'displayed as' is disabled and based on the field 'layer name'.
0
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0answers
22 views

Force refresh value defined by “data defined override” when export layout with PyQGIS 3.14

I am using the data defined override function to define the X and Y map grid intervals in the map layout. I want to export my map layout using pyqgis. But the map grid interval is not automatically ...
0
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0answers
26 views

Missing WMS legend graphic when exporting pdf using PyQGIS

I'm developing a PyQGIS processing script to automatically load some WMS layers and export them as part of a pdf map. I import the layout template from a file, which has the QgsLayoutItemLegend ...
4
votes
1answer
74 views

Transforming line into polygon with Geometry Generator

I would like to turn my line into polygon in the symbology. I found some hint here: https://anitagraser.com/2017/04/08/a-guide-to-geometry-generator-symbol-layers/ but I am not sure of the expression, ...
4
votes
2answers
189 views

How to get the slope from an elevation raster in QGIS?

I need to extract the slope from an elevation raster in order to do a species distribution model. It should be quite straightforward, but I can't seem to get it to work. I am running QGIS 3.10 on a ...
2
votes
1answer
51 views

Creating new column based on parts of strings in another column in QGIS

I have a column with zoning names (with "subzones" like UV036, UMTs2 etc.) and would like to create a new column with the general zone instead (UV instead of UV036, UMT instead of UMTs2... ...
2
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0answers
36 views

QGIS project wise grant to Users created in PostgreSQL [closed]

I have created multiple projects IN QGIS and saved them in PostgreSQL. It has created a table in Public schema as 'QGIS_Projects' and creates rows to save different projects from QGIS . I have given '...
2
votes
1answer
23 views

Selecting features based on great number of different values in the Attribute Table

I have many land parcels related to many different cities. I would like to select land parcels related to some of these cities only (about 20 of them). Is using LIKE/ILIKE + OR like below the only way ...
-1
votes
2answers
78 views

Add logo on layer to QGIS 3.10 using PyQGIS [closed]

How do I add any logo or img of any size on any layer using PyQGIS? Actually I want to add a watermark on a layer using PyQGIS.
2
votes
1answer
72 views

Selecting two or more values (like two city names) in one column

In the attribute table I have a column with many cities and want to select rows that only contain these city names, like "Paris" and "London". I tried: "cityname" ILIKE '...
1
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0answers
58 views

QGIS 3.14.1 not starting on my Laptop

After this QGIS doesn't start System config When double click on QGIS Desktop 3.14.1 is shows the screen as attached but after that the program does not start or run. I have also tried "run as ...
1
vote
1answer
302 views

QGIS 3.14 vs “no Qt platform plugin could be initialized”

Ever since updating to the most recently released QGIS stable version, 3.14.15, I am getting the error pop-up window: "This application failed to start because no Qt platform plugin could be ...
0
votes
1answer
29 views

Doing spatial join in QGIS between land parcels and zoning map, how can land use with biggest overlap give its attribute to parcel?

The parcel might have some small overlaps (or intersections?) from other land uses if the alignment of vertices is not perfect, I want to make sure the land use covering the largest part of the parcel ...
0
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0answers
20 views

QGIS 3.10 (composer) - Legend position changes when exporting the map

I know the question is quite old, since it was first asked here : QGIS map composer changing legend position when exporting atlas as images and here : QGIS composer changing legend position when ...
1
vote
1answer
29 views

How to add virtual (e.g. $area) fields to multiple layers

I wondered if I could add virtual fields to the feature tables of a number of polygon layers in a QGIS 3 project (or a geopackage). As an example, I would like to add the virtual field area (km²) as ...
0
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0answers
24 views

QGIS 3 Modeler: Generate New Vector File

I want my graphical model to create a new empty line layer (preferably as a temporary scratch layer) and then add a bunch of new columns to this layer (this part is easy using the field calculator). I ...
0
votes
0answers
29 views

Displaying raster data by clicking on a field in an vector attribute table using QGIS 3

I am doing the following using QGIS 3: Georeferencing of raster files. Digitalization of polygons (which are in this raster). It is often necessary to check how well the raster was digitized. To do ...
10
votes
0answers
286 views

High PostgreSQL/PostGIS memory and disk usage when saving QGIS project

Why would simply pressing the "save" button in QGIS cause my local PostgreSQL instance to cause memory and disk usage to spike to "Not Responding" levels? Seems to me like the ...
2
votes
1answer
26 views

Select features that do not intersect with another polygon in QGIS

See the image below. What I want to do is select all features that do NOT intersect with the features of the selected layer. How do I go about doing this?
3
votes
2answers
78 views

Add tabbed fields within QField

How can data be organized in tabs within Qfield? The "Advanced Bee Farming Demo" that comes with QField displays data organized in tabs (see picture below: General, Picture, Issues, Review, ...
1
vote
0answers
29 views

Creating data driven field on attribute table in QGIS [closed]

I want to create a Field on an attribute table, whose data will depend on another field within the same attribute table.
0
votes
1answer
43 views

OS VectorMap Local not styling RailCLine and RoadCLine

I am running QGIS 3.14.1 (64 bit version) on a Windows 10 PC. I have downloaded two 5km tiles of the VectorMap Local (3 July version) in Geopackage format. My Parish Council holds the relevant OS ...
3
votes
2answers
92 views

Circular clipper in QGIS

In QGIS 3.14 I wish to clip a layer to the features within a circular area. Can this be done?
0
votes
0answers
24 views

QGIS 3.x API: apply rotation based on the “angle” field of the imported SHP-File

I am writing a python code in Anaconda (Spyder). The goal is to create automatically a QML-File for my SHP-Files (categorized with the values of one of the fields). I have read the documentation on ...
2
votes
1answer
45 views

Set default input Vector Features in model

I have a Graphical Model with ~10 input Vector Features. Every time i execute it I have to set all 10 features manually. Isnt there a way to set default input values so I dont have to point at the ...
1
vote
0answers
34 views

QGIS and R bridge for spatial analysis

Currently I want to use the R geospatial tools within QGIS for carry out several models related to creation of random points inside polygons based on attribute values with the purpose of establishing ...
3
votes
2answers
143 views

Getting latitude / longitude in the QGIS Raster Calculator

I have raster files in the good and old EPSG:4326 (WGS-84) and I would like to create two other raster files with the exact same extent and resolution of it, but with the first raster having the the ...
1
vote
2answers
47 views

Zonal Statistics in QGIS 3

I moved from QGIS 2 to QGIS 3 I cannot seem to be able to use the zonal statistics package. Basically what I want to do is take the world pop GeoTIFF for a country and then calculate the population ...
1
vote
1answer
34 views

Acessing fields of created features in your PyQGIS

I'm new using PyQGIS 3 and I'm wondering how to access the field information from a layer generated by script. inside my processAlgorithm function I have the following: alg_params = { '...
1
vote
0answers
16 views

Increasing size of legend symbols in QGIS3.12.2 print layout

I have pixels with a fixed size on the map, as they have a certain resolution. Now in the legend of the print layout the symbols have the same size as the pixels on the map. I want to increase the ...
1
vote
1answer
26 views

Standalone script creates unwanted directories

I use the following code to import the relevant modules and prepare for a standalone script for QGIS 3.14: # Import modules import sys from qgis.core import QgsApplication from qgis.analysis import ...
1
vote
1answer
51 views

Lines Between Coordinate Points

Currently, I'm mapping data from the Hudson's Bay Company Archives in the nineteenth century, and I am tracing the routes travelled by fur traders. I have gone through the documents, recorded the ...

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