Questions tagged [qgis]
QGIS is a cross-platform GIS application licensed under the GNU General Public License.
6,994
questions with no upvoted or accepted answers
15
votes
0answers
1k views
Digitizing in stream mode in QGIS, using a tablet?
How to 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, ...
8
votes
0answers
254 views
Producing time-space cube in QGIS?
Although I have seen many examples about doing this at ArcGIS Desktop, I am still trying to find a how to using QGIS. What I want to do is something like the image below.
8
votes
1answer
414 views
Point cluster symbology for different categories without overlapping symbols
I'm trying to visualize crimes based on if the crime happened during day or night time. I've tried using the point displacement tool but I'm not satisfied with the results because the readability for ...
8
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 16bit image, as 8bit is giving a terracing effect.I believe I ...
7
votes
0answers
166 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 ...
7
votes
0answers
1k views
Joining segments of a line in QGIS?
I have lots of different lines composed of hundreds of segments in a Shapefile.
I would like to join them spatially where every start (or end) point of a segment correspond exactly (or within a range ...
7
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 ...
6
votes
1answer
89 views
Creating raster from point values
I have a raster whose pixel values are 0 or 1 (b/w areas in the image below) and data type is Float32.
I made a point layer from each individual pixel's center. Then I made some calculation for all ...
6
votes
0answers
92 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
0answers
68 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
0answers
1k views
Function in R to get difference between two sets of polygons comparable in speed to QGIS
I have two very large polygon shapefiles for which I need to calculate the difference between the two shapefiles. One is a shapefile of forest polygons, the other is a shapefile of road polygons. I ...
6
votes
0answers
559 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 ...
6
votes
1answer
306 views
Setting grid in QGIS that automatically adjust its intervals?
I am setting a template for multiple maps in QGIS 3 Layout and i was wondering if there is a way of automatically adjusting the grid's interval as a function of the scale of the map?
I did a bit of ...
6
votes
0answers
389 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....
6
votes
0answers
379 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
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 ...
6
votes
0answers
571 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 ...
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
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
1answer
257 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
0answers
117 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 ...
5
votes
0answers
146 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 ...
5
votes
0answers
131 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 ...
5
votes
1answer
144 views
Rasterize/Filter with Burn and Weight variables in QGIS
Using QGIS 3.10.1, I am attempting to rasterize some demographic polygons, and then apply a filter (Gaussian) to create a smooth/graduated surface. This works fine for some of my values (e.g. total ...
5
votes
0answers
184 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
3answers
244 views
Concatenate string field in spatial join in QGIS
I'm doing a spatial join between a point layer and a polygon layer. The point layer has a field called "type" which has string values. When I join this to the polygon layer, I would like to get a ...
5
votes
0answers
53 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 ...
5
votes
0answers
260 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 ...
5
votes
0answers
711 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
130 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
126 views
Finding easiest path to walk on topographic map?
I want to make the shortest path between two points, but the thing is that there's a hill in the middle. I used Naismith's rule to calculate how the slope interfers in the walking time and I did the ...
5
votes
0answers
64 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 ...
5
votes
1answer
136 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
158 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
920 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
298 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 ...
5
votes
0answers
396 views
How to print automatically Map themes in Label's Map Composer?
This expression [%@project_path%] prints the path of the qgis project.
How the Map Theme used in the layout can also be printed automatically ?
According to QGIS documentation, a Map Theme is a ...
5
votes
0answers
671 views
QGIS 3.4.1 Extensions Repository not available
In my QGIS 3.4.1 installation (Windows 10) the extensions repository says "unavailable", like in this older post: Why I can't install plugins?.
I already added the repository with "HTTP" instead of "...
5
votes
0answers
408 views
How to export “solid” 3D objects from QGIS to DXF?
I work in architecture and we often have to create urban contexts for our projects which involves obtaining a building footprint file and then extruding them by hand.
I have attempted to use QGIS (v3....
5
votes
0answers
183 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 ...
5
votes
0answers
394 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 ...
5
votes
0answers
91 views
Using the height of river to approximate its extreme flood boundaries - terrain analysis in QGIS?
Using QGIS I'm trying to analyse an area/DEM with this criteria: - heights 10 meter above the river-centerline in both sides of river.
I can do it with the calculation of contours (2m) from DEM and ...
5
votes
0answers
292 views
Is there a specific tool to globally manage visibility/theme in QGIS?
In short : I'm looking for a Visibility Manager (QGIS 2.18) ou Theme Manager (3.0).
I couldn't find it in the QGIS plugin list or in different methods on gis.stack. Maybe I missed it and maybe it ...
5
votes
0answers
616 views
When does a QGIS .qix spatial index of a shapefile need to be re-created?
I understand the basics of spatial indexes but would like to understand when exactly a spatial index would need to be re-created or updated?
The reason I ask is because when a folder was moved to a ...
5
votes
0answers
139 views
Speed execution of PyQGIS algorithms
I don't understand why if I do "manually" some algorithms I get results much faster than when I insert the same in a pyqgis code (with the same input).
This happens, for example, with the extract ...
5
votes
0answers
113 views
Different fonts in QGIS2threejs
I'm working with QGIS2threejs for quite a while and it is a great tool!
Changing font for the 3D presentation is easy, just change it in the css file.
But here is my question:
Is it possible to change ...
5
votes
0answers
693 views
Error running r.thin in QGIS
I get the following error when running r.thin:
Traceback (most recent call last): File
"C:/PROGRA~4/QGIS3/apps/qgis/./python/plugins\processing\algs\grass7\Grass7Algorithm.py",
line 395, in ...
5
votes
0answers
105 views
Speed up identify in QGIS
I have just transferred my Postgis database onto an RDS server, and there is a bit of a performance hit when using the Identify tool in QGIS (3) compared to localhost. I presume this is mostly network ...
5
votes
0answers
205 views
Voronoi Polygon Algorithm seems to exclude a Point from processing
I am using the QGIS (2.8.1) Voronoi Polygons Algorithm on a point shapefile.
See image below, the red triangles are the points I am using.
The resulting polygons miss a part (around HP87).
Any ...
5
votes
0answers
180 views
show relations between polygons by highlighting polygons
Is it possible to show relations (for example traffic flow) between polygons (for example counties) by highlighting related polygons by doing a query on a start polygon using QGIS?
Here is an ...
