Questions tagged [virtual-layer]
A QGIS vector layer that is a database view built using SQL over other QGIS layers.
215
questions
3
votes
2
answers
164
views
Changing values where two geometries are equal otherwise keep value with QGIS Virtual layer
I have two line layers in QGIS, of which one layer (layer 2 - yellow in the image) is a geometrical subset of the other (layer 1- blue in the image). The two layers also differ in their values of a ...
- 1,753
4
votes
1
answer
59
views
QGIS Virtual Layer Query containing JOINS always ends up having zero results
I've got a problem JOINing together several PostGIS tables (with or without geometry) in a Virtual Layer in QGIS 3.36.3
As soon as I use a (inner) join the the layer query statement, the result set is ...
- 53
0
votes
0
answers
37
views
Create distance buffer for virtual layer with categorized symbology QGIS 3.34
I want to create a virtual layer with a fixed buffer distance e.g. 1000 m from a buliding layer as input. The building layer contains information about its use in colum X of its attribute table. The ...
- 107
3
votes
1
answer
132
views
Filtering subset of records to be used in subsequent SQL statements
I recently posted this question, where the answer involved SQL and a Virtual Layer. In that situation, the SQL acted on the entire input layer, with the output exactly as desired.
Now I would filter ...
- 8,192
0
votes
0
answers
41
views
QGIS 3.34.5 LTR Virtual layers Crashes
Migrating from 3.28 to 3.34.5 I have a virtual layer that is causing crashes.
I am using a virtual layer to union 3 layers together to simplify the number of layers.
I have simplified the layer and it'...
- 1,726
0
votes
0
answers
26
views
Create virtual layer out of three tables
I have a problem with creating a virtual layer.
The issue is from a bad Database where the line geometry id is linked to non-geometry tables where the other information is included. In case this is a ...
0
votes
0
answers
31
views
Adding a virtual layer leads to slow perfomance and crashes in QGIS 3.36.1
I am creating a QGis project to help us track regular visits to specific properties in a small area. In order to do that I have the property cadastre layer which contains around 10000 individual ...
- 91
2
votes
1
answer
54
views
How to create a Virtual layer with point geometry and count repetitions from 3 different tables [closed]
From 3 tables with the following fields:
PARENT_TABLE
CODE1
CODE2
XCOORD
XCOORD
12395
8604813EG7180S0001GX
418477,91
4620364,53
13505
8604813EG7180S0001GX
418477,91
4620364,53
12968
...
- 1,142
3
votes
1
answer
147
views
How to create a Virtual layer with point geometry and count repetitions
From a table with the following fields:
CODE1
CODE2
XCOORD
YCOORD
162
6605548EG7180N0001SF
418596,65
4620206,74
196
6604802EG7180S0001SX
418477,91
4620364,53
196
6604802EG7180S0001SX
418477,91
...
- 1,142
3
votes
1
answer
107
views
Generate dynamic sum of attribute values from one layer based on overlap with polygons on another layer
I'm using QGIS 3.28 on Windows. I'm trying to make a workflow for determining whether a proposed lot satisfies minimum lot sizing based on soil type composition.
I have:
a single-polygon overall ...
- 93
2
votes
1
answer
24
views
How do I use SQL and virtual layer to draw a line from one polygon to another in the same layer?
Background:
Sometimes in modelling hydrology (e.g. in SWMM) we have runon from one subcatchment area to another. These subcatchments are records in a shapefile. I want to show this situation as a line ...
1
vote
0
answers
69
views
ST_Project in QGIS Virtual layers or SQL Query
Is there an equivalent to ST_Project that I can use for an SQL query for a virtual layer in QGIS
https://www.gaia-gis.it/gaia-sins/spatialite-sql-4.2.0.html
ST_Project( start_point Geometry, distance ...
- 1,726
3
votes
0
answers
77
views
Translate Geometry generator expression into Virtual layer Query
I have some expressions for drawing tree canopy zones ultimately I want to merge the zones for trees, hedges and woodland together but for now I would be happy if I can get the following expression to ...
- 1,726
1
vote
1
answer
50
views
How to add a virtual layer using ST_ClusterDBSCAN function
I have a 'POINTS' layer with 74 points geometry with the fields "NAME" and "ID". I want to add a virtual layer with the following query to calculate the clusters using the DBSCAN ...
- 1,142
3
votes
1
answer
56
views
Calculate area of polygons from one layer within polygon of second layer while matching criteria using virtual layers or field calculator QGIS
I have a polygon layer with classifications ('class'), and a second polygon layer of area of interest ('AOI'). I am trying to calculate the area of each of three classes within each (overlapping) AOI ...
- 1,133