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Questions tagged [qgis]

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

7
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116 views

QGIS versions yielding different results on $area calculations?

When grading an exam, I discovered that QGIS 3.2 and 3.4 produce different values on computing $area over polygons. I experimented using $area and area($geometry) to check the differences between ...
7
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0answers
216 views

Is it possible to open MapGIS files ( .WL, .WP & .WT ) in QGIS or other GIS?

We received some files from clients located in China created in a program called MapGIS. I was wondering if anybody knows how to make QGIS or any other GIS program, excluding MapGIS, open these files? ...
7
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0answers
1k views

How to force geometry type in mixed geometry WFS layer in QGIS?

I have an external WFS source serving mixed geometry types - in other words, I have no control of the source. When adding the layer QGIS sets the geometry type to line and thus I am unable to style ...
7
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0answers
360 views

Accessing existing instance of QGIS from 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 ...
6
votes
0answers
125 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 ...
6
votes
0answers
79 views

Show Symbol (e.g. City-Marker) only when an associated label can be displayed

I'm building a map for a certain region with many cities to be displayed. Some of the smaller cities should only be displayed if they don't overlay bigger cities. While the labels of the smaller ...
6
votes
0answers
2k views

Rasterize shapefile using another raster's size and resultion

Rasterizing a vector (shp) I face the following problem: I want my output file (the rasterized vector) to have the same resolution and dimensions as an existing raster. If I understand the interface ...
5
votes
0answers
51 views

Cumulative value/cost along shortest distance roads in QGIS

I have a road network linking multiple (ca 1830) agricultural production regions to several ports (ca 12). (lines in the pic below are roads, small black dots centroids for producing regions and ...
5
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0answers
52 views

Offline editing slides the attribute data over one column and ads an “fid” column

My QGIS 3.4 Madeira project is attached to a PostGIS database (Azure) and looks good. It contains two layers, one with points and one with polylines. Each item in the Pointz layer has about ten ...
5
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0answers
69 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
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0answers
126 views

Unattended QGIS updates with OSGeo4W

I would like to do an unattended update of my QGIS install every night using windows task scheduler. Is it possible to automatically update all installed packages with the OSGeo4W-Installer without ...
5
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0answers
590 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
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0answers
292 views

Calculating average pixel value for each band across multiple raster layers?

I have a set of raster files that are essentially data sets of precipitation across a region. I have multiple raster files that are the outputs of different climate models. Each pixel in the raster ...
5
votes
0answers
171 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 ...
5
votes
0answers
102 views

Render only features located around the the mouse cursor in QGIS?

When hovering over a vector layer in QGIS for feature selection, it would be useful, if only those in a buffer of a certain distance to the mouse cursor are displayed. Any ideas on if/how this might ...
5
votes
0answers
114 views

Calculating Mean and Sum in QGIS Zonal Statistics?

When a polygon intersects more than one pixel, and each pixel within the polygon occupies a different area, does the mean take into account the area of each pixel and its correspondent value (i.e. ...
5
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0answers
123 views

Value relation autocompletion and dropdown menu in QGIS?

I use a value relation widget which is connected to a list of streets. If I tick "use completer" I can use the autocompletion but the dropdown menu disappear. The dropdown menu appears again only if ...
5
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0answers
501 views

QGIS select by location failing

I'm performing a simple select by location. I want to select polygons from TQ_Building that fall within rapidair_AOI, a larger polygon. My workspace looks like this: I'm using QGIS 2.18.13. I've ...
5
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0answers
185 views

Packing squares polygons in a raster grid

In the green area of the raster I have to fit as many square polygons as possible, of three different sizes: 3x3 cell size 2x2 cell size 1x1 cell size With the fact that the approach should be ...
5
votes
0answers
97 views

Issues with atlas generator and labelling across maps/images

I have a lot of layers in my project and I am trying to use the atlas generator in the print composer to create a tiled map. Some of the layers have labels which have different configurations with ...
5
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0answers
91 views

Preserving Vector Attribute Types When Processing Vectors

Qgis seems to change vector attribute types for certain processes. Is there a way to force preservation of the attribute types? My situation: I have five vector layers I want to merge, all shapefiles,...
5
votes
0answers
357 views

Display pictures stored as bytea in postgresql column in qgis

does someone knows a possibility to visualize in a bytea column saved photos of a postgresql database in qgis? I would like to store pictures directly into the database, not just the link/ url.
5
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0answers
306 views

QGIS Referencer: Tranformed Failed

I'm using a new install of QGIS 2.18.2 on an iMac running OSX 10.10.5. I create a new project. I use the OpenLayers plugin to show an OSM background of a part of Mayfair in London. I now use the ...
5
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0answers
704 views

Build QGIS 2.16.3 on windows 7 SP1 x64

I'm trying to learn how to build QGIS from source perfectly with windows 7 x64 to adapt QGIS for a urban planing. But I get plenty of errors. Until now this is what I'm doing: PART1: VISUAL STUDIO ...
5
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0answers
399 views

QGIS Align Rasters how to retain pixel values?

I am attempting to align and then merge a number of rasters of the same resolution and extent, but where the pixels are slightly misaligned (creating small gaps when merged). This works fine using the ...
5
votes
0answers
2k views

How to use 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 ...
5
votes
0answers
825 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 ...
5
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0answers
741 views

How to digitize 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, ...
5
votes
0answers
853 views

Print Composer Template produces empty map?

I have a print composer template which I'm trying to populate with different subset queries from a CSV-derived vector layer using the Python API. However, all the output PDFs contain everything except ...
5
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/...
5
votes
0answers
648 views

How to debug Quantum GIS PlugIn Visual Studio DLL?

I have developed a Quantum GIS plugin layer using Microsoft Visual studio and placed it in my plugins folder of my customized QGIS application. I now intend to debug the DLL using Microsoft Studio. ...
4
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0answers
23 views

How to use Layer Parameter variables in Field Calculator within a 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 ...
4
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0answers
41 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 ...
4
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0answers
213 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 ...
4
votes
0answers
173 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 ...
4
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0answers
265 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 "...
4
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0answers
56 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 ...
4
votes
0answers
113 views

Question marks (“?”) in QGIS layer panel when using svg markers defined with “Data defined override”

When using svg marker symbols and set the path to svg file via Data defined override the svgs display well in the map canvas, but not in the layers panel (applies for QGIS 2.x and 3.x). svg marker ...
4
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0answers
169 views

How to use a WCS layer in QGIS for processing?

I have a GeoServer serving raster dem data out via WCS and can add the layer easily to QGIS (3.2) but when I try to use it as the input for an operation (e.g. HillShade) I get an error. Processing ...
4
votes
0answers
95 views

Offline editing solution for small GIS project with multiple editors?

I have a specific use-case that I cannot seem to find any solutions for online, so any and all advice would be most welcome. Some basic details: I am part of a small academic organization (a research ...
4
votes
0answers
76 views

Variable width buffer based on axis directions in QGIS

I need to buffer a polygon with a different distance in the x and y directions. I should add that my polygon has the following properties: closed (obviously) simple (no edge crossing, no more ...
4
votes
0answers
77 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 ...
4
votes
0answers
77 views

Adjusting georeferencing of GeoTIFF?

I have three thermal IR images of a boat acquired by a drone as it flew overhead. The images were taken at one second intervals, are GeoTIFF files and overlap one another. I don't know exactly how the ...
4
votes
0answers
54 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 ...
4
votes
0answers
133 views

Investigating PostGIS table not showing in QGIS

I created a table in Postgres: create table eric_zs as select z.id, z.name, st_multi(st_union(a.geom)) as geom, count(*) from geo_as a inner join geo_zs z on a."ZS_id" = z.id group by z.id, z....
4
votes
0answers
72 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 ...
4
votes
0answers
140 views

When does a 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 ...
4
votes
0answers
86 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 ...
4
votes
0answers
75 views

Halftone effect gridded points inside polygon

I am trying to create smooth looking polygons by gridded points in QGIS (2.18.16), with a fading effect towards the boundary of the polygons (halftone effect). By using the 'fillGrid' function from ...
4
votes
0answers
135 views

QQIS Automatically Converts UTC Date-Time to Local?

I imported a WFS layer from a geoserver into QGIS and also into a web service that is based on Cesium. The geoserver fetches the data from Elastic search and serves it out as WFS. The date-time ...