Questions tagged [qgis]
QGIS is a cross-platform GIS application licensed under the GNU General Public License.
7,713
questions with no upvoted or accepted answers
17
votes
0answers
1k views
Digitizing in stream mode in QGIS using a tablet
How can I digitize in stream mode in QGIS, using a wacom cintiq tablet?
Freehand it's no use. I need something like MNDR stream digitizing extension for ArcView 3.x, which allows continuous tracing, ...
10
votes
0answers
210 views
Processing post-execution script hook to clear scratch layers?
I've been cobbling together some Processing scripts for QGIS 2.18 (I'm not a fan of QGIS 3 scripts), and I keep running into one particular problem: my script creates a lot of scratch layers and they ...
10
votes
0answers
2k views
Exporting a 16-bit image from QGIS
Could someone explain how to export from QGIS a 16bit image?
I have imported data and coloured it as I want, but need to export it as a 16-bit image, as 8-bit is giving a terracing effect. I believe I ...
9
votes
1answer
109 views
Displaying Google Earth Historical Imagery in QGIS
I am currently carrying out research aimed at showing the evolution of plant cover in urban areas. I opted for the calculation of the vegetation index from Sentinel2 type images that I would like to ...
8
votes
0answers
332 views
Determining which QGIS layer has a spatial index?
I would like to loop over all layers within a QGIS project and determine which layer don't have a spatial index and cause QGIS to slow down.
I tried the method hasSpatialIndex() but this always ...
8
votes
1answer
3k views
Using MMQGIS hub lines tool in QGIS?
I am trying to connect source and destination points with the hub lines tool in MMQGIS. I have gone through the other posts on this subject but couldn't figure out what I am doing wrong.
I have ...
7
votes
0answers
105 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 ...
7
votes
1answer
308 views
Symbol in layers panel not visible
I have a layer with symbology that includes geometry generators. It would appear that because of these the symbol is not visible in the layers panel.
Is there a way to show the up most symbol (green ...
7
votes
0answers
72 views
Snap LineStrings considering direction in QGIS 3
I have 2 projected shape files: Roads (red) and public transit routes (blue):
I want to snap the PT routes to the roads, but because of inaccurate marks sometimes the routes are snapped to the wrong ...
7
votes
0answers
661 views
Add private plugin repository to QGIS 3.4
I want to add a repository to my QGIS 3.4 which is on a private server. The repository contains all files needed (plugin.xml and metadata.txt for example) and has the structure as described here:
Is ...
7
votes
0answers
486 views
Labelling a rubber band (QgsRubberBand)
It is possible to label QgsRubberBand or QgsVertexMarker with a text annotation (QgsTextAnnotationItem).
See this MWE:
...
r_polyline = QgsRubberBand(iface.mapCanvas(), False)
r_polyline....
7
votes
1answer
213 views
Use DEM elevation attributes in vector polygon?
I am modeling glacier retreat scatching polygons on DEM surface trying to come out with 3D scatch.
Is it possible to adjust "height" of polygon to follow elevation of DEM surface (eg. glacier height ...
7
votes
0answers
1k views
Is it possible to do parallel processing in GDAL and QGIS?
It seems like processing a large raster dataset in QGIS can cause a crash, for example in QGIS failing to complete clip or intersect and crash dump in qgis. Is it possible to use GDAL parallel ...
7
votes
0answers
590 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 ...
7
votes
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 ...
6
votes
0answers
37 views
Regex_replace in the Field Calculator: unexpected duplication of replacement elements
After testing things out for a different question, I found something unexpected about the way regex_replace works in the Field Calculator, compared to PostgreSQL. The suggested insert ends up ...
6
votes
0answers
152 views
When NOT to create spatial index
As I realized once again connected with this answer to Joining attributes by location using QGIS, creating a spatial index can result in huge performance improvements.
However, I was wondering why ...
6
votes
0answers
62 views
Does QGIS use data source-specific operations?
This may be a very basic question, but I couldn't find an appropriate answer.
Does QGIS use data source specific operations where available and appropriate? For example, when using the Join attributes ...
6
votes
0answers
135 views
Naming clipped layer according to the attributes of the mask layer in QGIS
I have calculated the dnbr for a fire season across a whole region, and I've clipped it using a mask.
The mask is a layer of ground survey plot locations because I want to find out the dnbr for each ...
6
votes
0answers
109 views
Multiple styles for GeoPackage
I am constructing a geopackage from vector layers that have values for number of years, each year is an attribute (1965, 1995, 2025, 2055, 2085). I have styled the layers and added the styles to the ...
6
votes
0answers
292 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-Tocher that give very different results. Linear ...
6
votes
0answers
78 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
...
6
votes
0answers
136 views
How to do a Lee’s Tetrahedral Conformal Projection of Antarctic/South pole on QGIS?
I want to do map of Antarctic using the Lee's Tetrahedral conformal map projection as the image below using QGIS version 3.4. Is it possible to make a custom CRS to do it? If yes, what's the ...
6
votes
1answer
95 views
Difference between merge and create virtual raster
I have the DEM of a defined region that has been split into sub-DEM with a resolution of 1 km x 1 km. When I merge the sub-DEM to create a single DEM (Raster -> Miscellaneous -> Merge), the overall ...
6
votes
0answers
458 views
Nearest neighbour joins for two geodataframes using KDtree from scipy/sklearn
I have a number of large geodataframes and want to automate the implementation of a Nearest Neighbour function using a KDtree for more efficient processing. The process I want to achieve here is to ...
6
votes
1answer
306 views
3-D Terrain effects for vectors in QGIS?
I'm a bit new to QGIS, and making a few maps of roads through mountains. I'm looking to have a 3-D effect within my 2-D map.
I got a DEM, made a hillshade, and blended a basemap over it. Nice ...
6
votes
0answers
91 views
Referencing an output in an expression in process modeler
In the process modeler, I'd like to reference an output of a previous step as one of the parameters of an algorithm. In this case, the previous step was clipping a large raster and I want to use the ...
6
votes
1answer
580 views
File naming iteration QGIS modeler
I am attempting my first use of the modeler from the Graphical Modeler from the Processing menu in QGIS. I made a simple model for cliping species data by sanctuary.It has two Vector Inputs, uses some ...
6
votes
0answers
209 views
Equal length dashed lines while using 'segments_to_lines' in QGIS
I want to create tapered lines with a dashed line stroke (to style intermittent streams).
I followed this tutorial to create the taperered lines, basically using Geometry generator with the expression ...
6
votes
0answers
496 views
Grouped “labels” for QGIS 3.0 Point Cluster styling?
I'm trying to make a cluster visualization of a vector point layer about trees with a few requirements:
The clusters need to change depending on zoom level (solved)
The clusters need to indicate how ...
6
votes
0answers
422 views
QGIS/Spatialite cluster analysis with density
beginner here
I am trying to analyse a large set of points (2 millions) over a set of polygons (3000), and particularly find clusters of points. Doing it in QGIS was taking too long/crashing the ...
6
votes
0answers
1k views
QGIS cannot open output layers
I have problem with QGIS 2.0.1. Everytime I run tool from SAGA or GRASS, I get exactly the same error, for example:
Oooops! The following output layers could not be open
Channel Network: /tmp/...
6
votes
1answer
303 views
Spatialite KNN view in QGIS
My task is to calculate the average ground survey level for each tree in my dataset, using the 3 closest survey points (optionally within a 3m radius of the tree). I want to write this in a Spatial ...
5
votes
1answer
90 views
Calculating the nearest neighbour using given road network in QGIS
I have the following information/layer:
Address points (point layer)
Points which represent the entries to urban green spaces (point layer) - I built these cutting the roads with the borders of a ...
5
votes
0answers
52 views
Using flags in new-style QGIS Processing Algorithms
In QGIS 3.6+, there are two different ways to construct a Processing Algorithm.
Defining a class inherited from QgsProcessingAlgorithm. In this case, I can define flags for an algorithm as follows:
...
5
votes
0answers
57 views
QGIS Geometry Generator not working for some features at some scales
I have a set of layers, one of them is labeled using geometry generator. Thing is, at some scales (1:800 and up) and some features (like 1/30) the geometry generator evalues to null geometry, so the ...
5
votes
1answer
111 views
Issues with exporting GeoPDF's in QGIS
I'm having issues exporting a georeferenced map from QGIS using version 3.10.4-A coruna. I've tried different (newer) versions of QGIS and also different computers and get the same error. Hoping some ...
5
votes
0answers
57 views
QGIS vector field marker not respecting map rotation
I’m working on a map the shows point displacement between two dates. These are survey benchmarks that are surveyed periodically to observe slope movement. Symbolizing this is QGIS is straight forward ...
5
votes
0answers
74 views
QGIS contextual menu overriding
I would like to override the default contextual menu in QGIS 3 in the ToC.
I've created a class that inherit from QgsLayerTreeViewMenuProvider.
from qgis.gui import QgsLayerTreeViewMenuProvider
from ...
5
votes
0answers
153 views
Getting layer id of processing step in QGIS graphical modeler for usage within aggregate() function
How can I get the layer name or layer id of the result of an processing algorithm within QGIS graphical modeler, so I can use aggregate() function in a later processing step? Is this somehow possible ...
5
votes
0answers
82 views
Clustering without aggregation with QGIS Point Displacement
I've seen the following map on twitter and am looking to create the same effect for point displacement.
I'm familiar with grid and circle point displacement as well as with clusters point to ...
5
votes
0answers
61 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 ...
5
votes
0answers
140 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 ...
5
votes
0answers
378 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 ...
5
votes
0answers
1k views
Why do the Heat Map (QGIS) and Kernel density estimation (SAGA) tools provide different results?
The Heat Map tool (QGIS) and the Kernel Density Estimation tool (SAGA) provide different results for the same data as shown below.
Why is this happening?
Is one of them more conceptually correct?
...
5
votes
0answers
149 views
Rotating image by specific angle in QGIS plugin
I am using the Freehand Raster Georeferencing code in a widget to help size and locate site plans on aerial GE backdrops. I need to find a way for a user to input a specific angle of rotation and the ...
5
votes
1answer
161 views
Nested rules in QGIS 2.18
I work with QGIS 2.18. I have a polygon shapefile with two atrributes: id (unique for each polygon) and type.
I visualize the shapefile using the "type" attribute, but I would like to add a nested ...
5
votes
0answers
174 views
Creating a segment for fixing water pipes and finding disconnected areas
I'm wondering if there is a tool for this problem. I'm using QGIS 2.14.2. Basically I want to select a pipe and find closest valves there is and to turn them off. After that I need to find all pipes ...
5
votes
0answers
1k views
Running OTB Random Forest Classification
I am having trouble processing a satellite image using the RF (Random Forest) classification, that is a machine learning algorithm in the Orfeo Toolbox of QGis 2.18.1.
When I run the Tool, the ...
5
votes
0answers
344 views
Old .qml style (vector-polygons) from QGIS 2.18 in QGIS 3.4
I have a .qml polygon style file created with QGIS 2.18. It works to import until Version 3.2 without problem. But in 3.4 the style is loaded, but not applied/visualized. The Polygons dissappear ...
