Questions tagged [qgis]

QGIS is a cross-platform GIS application licensed under the GNU General Public License.

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15
votes
1answer
586 views

Accessing existing instance of QGIS in stand-alone Python script

For my own data analysis pipeline, I am running a split screen setup with IPython notebooks on one side, generating variables from source data, pushing them to a CSV file which QGIS then reads/joins ...
13
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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, ...
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0answers
331 views

Open QGIS project files in exclusive mode / alert if project file already in use

I have QGIS-Project-Files saved to a network drive and was wondering if it is possible to warn users that a project file is already opened by an other user to prevent concurrent editing of the same ...
8
votes
1answer
388 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
1answer
314 views

Loading multiple shapefiles in GeoDjango?

I have 3 three shapefiles and would like to upload all of them and project the result in GeoDjango admin. a) state.shp (for the shape of a state) b) boundary.shp (to identify a specific portion in ...
7
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0answers
161 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
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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
0answers
163 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.
6
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0answers
78 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
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0answers
71 views

QGIS 3 Display negative values bar diagrams

Suppose I have a dataset with an id (for each geographic entities) and 2 numeric fields NUM1 and NUM2. These numeric fields have positive and negative values. When I use bar diagrams, only theses ...
6
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0answers
65 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
506 views

Fixed QGIS layer symbol size in layer legend

When a layer symbol is defined with map units or "meters at scale" unit, it is sometimes shown in the legend at a very small scale, preventing to see the details. Or if we zoom in the map, the legend ...
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
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0answers
511 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
262 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
363 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
125 views

Single Sided Buffer Error QGIS

I have delineated a shoreline and created an offset "buffer" of 75' and 250'. When projected onto the screen it appears as though a computation error has occurred and the buffers extend onto the left ...
6
votes
0answers
275 views

Using transform function in QGIS layer geometry generator?

I'm trying to use the following expression in the geometry generator in a QGIS layer to show a 1-mi boundary around points: buffer(transform($geometry, 'EPSG:4326', 'EPSG:2877'), 5280) However, the ...
6
votes
0answers
369 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
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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
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0answers
569 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
248 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
115 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
121 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
108 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
130 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
48 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
204 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
587 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
38 views

QGIS shared project (monitor changes)

I have a software-development background with a powerful use of svn and git. I work now for a public authority with two offices far from one another. Two other colleagues and I are sharing several ...
5
votes
0answers
123 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
0answers
109 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
63 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
123 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
156 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
853 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
281 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
365 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
623 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
350 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
169 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
367 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
88 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
259 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
521 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
134 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
106 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 ...

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