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Questions tagged [qgis-3]

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

0
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0answers
14 views

Disconnect between raster symbology in Layers Panel and Layer Properties (QGIS 3)

I'm working on a Python plugin for QGIS that applies a customised colorRampItemList to a single band raster. The result displays correctly on the map and in the Layers Panel but incorrectly in the ...
0
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0answers
9 views

Unable to save point features to QGIS on MySQL database

I created a table with point geometry in MySQL. Subsequently added a vector layer from MySQL table. The table could be accessed from QGIS. However on pressing the add button the system threw warning ...
1
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0answers
18 views

Boolean input in Python 3 Script?

in QGIS 2.18 I had this script ##formula_1=boolean ##formula_2=boolean ##formula_3=boolean ##result=output string if formula_1 == True: result= 1 elif formula_2 == True: result= 2 elif ...
1
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0answers
20 views

Modeler with optional inputs or none?

I have a need for a model that all the input may be optional and allow the "Selected features only" option. So, I developed a model that fakes it all as seen in the example below I realize that some ...
2
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0answers
54 views

Method in QGIS to do a select by radius but ignore “islands”

I am looking for a process in QGIS to run a selection from a given point based of a radius that ignores "islands". For example you may have a body of water which acts as a natural barrier past which I ...
1
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0answers
22 views

processing.runAndLoadResults() does not load the result QGIS 3.4.5

I am trying to execute an algorithm and load it in the layer tree when it is done. After looking online I saw that I could use processing.runAndLoadResults() to load my result when the algorithm is ...
0
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0answers
28 views

Using import photos plugin in QGIS?

I have some geotagged photos saved on a network drive which I want to import into QGIS 3.2. I have installed the import photos plugin. I have gone through the import photos process and selected the ...
1
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0answers
22 views

Detecting checking/unchecking of rules in a rule-based rendering using PyQgis [on hold]

Is it possible to programmatically detect checking/unchecking changes of a rule in a rule-based rendering ? I found no indication of existing signals .. I got lost reading QgsVectorLayerRenderer ...
1
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1answer
42 views

Efficiently query two properties QGIS spatialite

I have a simple query that involves two steps: non-spatial criteria (should be super-fast) spatial criteria (which is really slow) I would like to run the spatial query only on the filtered layer (...
1
vote
1answer
26 views

Getting QGIS Model Processing Raster Calculator Error?

I am using "raster calculator" tool of the saga in my model. The tool correctly executes raster operation like "a * 2" in value formula option but the same expression is not executed pre-calculated ...
1
vote
1answer
38 views

Can we call a single attribute entry (=one row) “a feature” of the Layer? [on hold]

For the single layer(for example Airport layer) there are many entries in the attribute table. Can we call single attribute row entry a feature of the Airport Layer? Can somebody give clear view ...
4
votes
1answer
72 views

Deleting features in PyQGIS?

I am comparing geometries of input layer and output layer features. I want to delete features in output layers which has equal geometry to input feature. I am using following code to do that. for ...
3
votes
1answer
27 views

Specifying snap raster in QGIS?

I am deploying QGIS 3.6 on Windows 10. Using the Raster > Projections > Warp (Reproject) tool, I need to reproject a single-band, float32, GeoTIFF DEM from EPSG:3413 to EPSG:3857. The output ...
1
vote
1answer
41 views

Points Layer to Distance Matrix QGIS 3.6 - Noosa

I'm trying to calculate a sample distance matrix from four points in the BNG CRS: Using Vector-> Analysis Tools -> Distance Matrix, I get: Input point layer is a MultiPoint layer - first convert to ...
2
votes
0answers
42 views

Adding new field and calculating in PyQGIS

I'm trying to write a script using QGIS 3.4. What I want to achieve is an Excel-style calculation where I can create a new field "field2" and calculate the difference between a current and previous ...
0
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0answers
15 views

3D Visualization Error

I am having an issue utilizing 3D Visualization. When I access New 3D Map View, the map that shows up is a 2D representation. Seeing this, I navigate to the 3D configuration tab (represented by a ...
2
votes
0answers
37 views

Mouse pointer always “in work”

I used QGIS 3.2 Bonn and suddenly, and I don´t know why, the mouse pointer never stops rotating as the project is in work. It is still possible to click and select things like it is possible with the ...
-2
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0answers
47 views

Migration flow maps with QGIS 3.6 [closed]

I want to make flow maps with QGIS 3.6 but without using the FlowMapper (because it doesn't work)
2
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0answers
27 views

Create filter expression by selected elements?

Is it possible to automatically create a filter expression for the Query Builder by selected elements?
1
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0answers
23 views

Remove and reload raster layer from previously created QgsRasterLayer object

I have created a QgsRasterLayer object using: lyr=QgsRasterLayer(url,'lyr_name') and the layer is displayed by: QgsProject.instance().addMapLayer(lyr) Now when this layer is removed through: ...
1
vote
1answer
43 views

Showing only one feature per Report page in QGIS 3

The gift of Reports in QGIS is a massive step in the right direction. I have set up a department template for my team to use and it looks great! Right now, I am attempting to setup a report that will ...
4
votes
0answers
38 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 ...
1
vote
1answer
47 views

How to integrate QGIS 3.4 with the DE theme

I just got the upgrade to QGIS 3.4 from the ubuntugis-unstable PPA. One thing that immediately stands in this version is that it ignore the DE theme, instead yielding an unhealthy white-based theme. ...
-4
votes
0answers
31 views

Difference between definitions “feature” vs. “layer” [duplicate]

What is the difference between the two definitions "feature" vs "layer" by means of GIS? Especially in QGIS (PyQGIS) is there any difference to say "feature" or "layer"? For example, I have the ...
2
votes
0answers
37 views

How to get raster layer metadata in python for QGIS 3.6? [closed]

I am loading imagery as raster layer through a URL. I need to store its metadata as JSON string in db for future reference. I tried getting the metadata via layer.metadata() and then tried to get ...
1
vote
1answer
13 views

Rule for labeling ways not being part of OSM relation in QGIS

A brief overview of what I want to achieve: Create a map showing all cross-country ski trails in a specific region with some customizations/styling on them. The data come from OpenStreetMap ...
1
vote
2answers
39 views

QGIS 3.4 / QgsVectorLayer()

I tried to use QgsProject.instance().addMapLayer(layer) on QGIS 3.4 but I didn't succeed. Example: layer = QgsVectorLayer(r'C:\CURSO_PYQGIS\CAPAS\urbano.shp','urbano','ogr ') QgsProject.instance()....
3
votes
0answers
40 views

Finding path between points on limited road network

I am struggling to find a path between health facilities in Madagascar. I think that because the road network (from OpenStreetMap) is limited, the functions in QGIS, such as v.net.distance and ...
3
votes
1answer
32 views

Issue converting CSV files to point shapefiles using pyqgis - QGIS 3

I have hit a snag using pyqgis in QGIS 3. I want to convert a set of CSVs (20 total) into point shapefiles but I am struggling with just the single CSV case. My code is based on this blogpost (https://...
3
votes
2answers
60 views

QGIS SAGA functions failing “… following layers not correctly generated. …” [on hold]

I've been having an issue with the SAGA functions for a while now, I believe since upgrading to one of the early 3.x versions. No matter which function I use they all fail with the same error (...
0
votes
1answer
28 views

How do I make a map's background transparent in a layout?

I am trying to add an overview map to my layout. The main map is projected while the overview map is a 'globe' (image below). I want to make the white part of the overview map transparent. I have ...
1
vote
3answers
63 views

Adding tile layer via PyQGIS

Any idea how to add a tile layer (XYZ-Layer) using PyQGIS 101 to a map? Something like osmLayer = QgsXYZLayer(uri.uri(), "OpenStreetMap", "XYZ") "XYZ" is a raw guess. Running QGIS 3.6.0
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0answers
18 views

QGIS Heat Map output not correct

Fairly new to QGIS here. I'm having trouble creating a heat map in QGIS3 from a set of points. I've followed what others have done online (e.g.: https://www.youtube.com/watch?v=o9Gqrr5cYrY) but in my ...
1
vote
0answers
18 views

pyqgis 3:how to identify partial intersections between a buffer (polygon) layer and pipe (line) layer?

I have a drains layer (polygon) around which I have created buffers of varying distances. I want to find the intersection between the different buffer layers and pipes (line) layer and accordingly ...
-2
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0answers
24 views

Listing all layers of legends using PyQGIS? [duplicate]

I want to list all of the available layers of layer panel in console using PyQGIS.Can you please suggest class and methods to do so.
1
vote
1answer
54 views

QGIS 3 Processing Script refer to input layer

I'm new to Python and trying to figure out how to write my first Processing Script using QGIS 3.6 on Windows 10. I'm using the default template provided in QGIS 3 (Toolbox > New script from template)....
1
vote
1answer
45 views

Resolving blanks when calculating attributes for almost 2 million polygons in QGIS?

I am starting with this Hazard Parcel Exposure dataset from the Metropolitan Transportation Commission which I downloaded as a shapefile. http://opendata.mtc.ca.gov/datasets/parcel-hazard-exposure ...
1
vote
1answer
63 views

Generating map tiles with QGIS 3.6?

Similar to this rather dated question, is there a way to generate map tiles on QGIS 3.6? The plugins linked from that question only support QGIS 2.x. I wonder if things have changed in QGIS 3.x ...
3
votes
0answers
46 views

Automatisation of isochrone map creation in QGIS 3

I need to measure the area of isochrones for a big number of points, for different time thresholds and for different means of transport. I've been using the plugin isochrones in OSM tools with QGIS 3....
0
votes
1answer
26 views

PyQGIS3 retrieving points from a shortestpath graph

I'm upgrading some code which worked with QGIS 2.18 to now work with QGIS 3.4.5 and had the following snippet working to retrieve a set of points from a graph created by the QgsGraphBuilder function: ...
2
votes
0answers
32 views

Extract derived data fields from Shapefiles

I've uploaded shapefiles with professionally supplied survey data into QGIS and it all plots fine, then when I export the attributes table into Excel I see that the XYZ values are all zeros. I know ...
2
votes
0answers
21 views

What is stored in Options|Advanced|PostgreSQL|connections|dbname|keys group in QGIS 3?

Since QGIS 3 in the Options|Advanced|PostgreSQL path referred to in the title there is a new group 'keys' as can be seen in this screenshot: In old QGIS 2.X: What kind of information is stored in ...
2
votes
0answers
15 views

QGIS 3.4.5 Attribute table expression in print composer not working

I just upgraded from QGIS 2.18 to the latest stable release (3.4.5). I am trying to filter an attribute table added to a layout by using @atlas_pagename and I can see there is a match in the ...
1
vote
0answers
15 views

single sided buffer in pyqgis 3 gives “_core.QgsProcessingException: Error calculating single sided buffer” error

I am trying to create a single sided buffer around drains (polygon shapefile). The Distance parameter must be taken from a field in drains shp. Here is my code: buf_out = self.dlg.lineEdit_3.text() ...
2
votes
1answer
61 views

Calculating the number of lines for each pair of origin/destination point - QGIS3

I have shapefile that looks like this: I need to make a matrix (or just to add a couple of fields in the attribute table, something like the origin-destination matrix), which will have the number of ...
0
votes
1answer
22 views

Label point layer with attribute of surrounding line features (QGIS 3.x)

I would like to label the points of my point layer with the name attributes of the surrounding line features. The result should be a list, with the names of all lines next to the point (f.e. 10 map ...
3
votes
1answer
47 views

Dynamically color labels in color of features (QGIS 3.x) [duplicate]

How do I dynamically color labels in the color of the labeled feature? As you can see in the screenshot, the lines are in different colors, but the labels are just in black. As I know, I have to set ...
2
votes
2answers
60 views

Error Loading QGIS 3

Couldn't load plugin 'processing' Every time I load QGIS 3.4 I get the below error ImportError: dlopen(/Library/Frameworks/SQLite3.framework/Versions/E/Python/3.6/sqlite3/_sqlite3.cpython-36m-...
0
votes
0answers
22 views

Developing and desirably debugging pygis-3 processing scripts?

The writing of processing scripts in QGIS3 changed substantially. On the basis of many tutorials/blog posts and answers on this site I got a running processing script in QGIS3. But it was, for a lousy ...
1
vote
1answer
57 views

QGIS 3.6: Vector “Polygons to Lines” missing

I use the tool Vector-->Geometry Tools-->Polygons to Lines all the time. It is in the menu up until 3.4. In 3.6, that menu item is no longer available. Where did it go? Is there another way to do ...