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Questions tagged [qgis]

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

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153 views

Single value of raster displays as transparent?

I have a GeoTiff raster that I'm trying to style, but a single value (1 of 8) refuses to take on any color. It always displays as transparent. Any idea of why this is / how to resolve it? Working in ...
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154 views

Add r.null functionality to GRASS toolbox algorithms in QGIS

I'd like to be able to use GRASS's r.null operation in the QGIS processing toolbox (not via the GRASS plugin). However, it doesn't seem to be available. How would I go about adding code to allow for ...
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31 views

Problem in cell dimension assignment from “save as” in QGIS

I am trying to save one raster in QGIS by changing the cell dimensions. I select 30 x 30 as cell resolution, but then the output raster has a resolution of 29.9985 x 29.9985. How can I assign exactly ...
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65 views

Why do merged rasters in QGIS look 'patchy'?

Poor title for this question, but I can't think of a better way to explain it. I have merged two rasters. I want the joins to be seamless, but there is an obvious line where they meet... I've tried ...
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200 views

QGIS 2.14.3 very slow when saving edits on Ubuntu 16.04

QGIS 2.14.3 "Essen" is really very slow when saving edits on a single layer (point features) on Ubuntu 16.04 64 bits. There is only about 100 points in this layer. In editing mode, when saving, it ...
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227 views

Extract specific altitude curve from raster

Is there any way one can extract a specific curve from a raster DEM qith QGIS? I know I can extract all curves, specifying the desired altitude interval between curves. But I was interested in ...
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284 views

Why does ST_Area in SQL give a different value to $area in QGIS?

The area value I'm getting using the SQL term 'ST_Area' is markedly different from that gained from QGIS functions like $area, the area measure tool and area as a derived feature (all of which agree ...
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216 views

Connect two points with fixed longitudinal slope over DEM - QGIS

Is it possible to connect two points with fixed longitudinal slope over DEM terrain or connect points with maximum longitudinal slope? Make road line between two point, for example 7% or make it with ...
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47 views

Shapefile CRS conundrum

In QGIS I have two vector layer shapefiles which should overlay approximately one on the other. They have both been downloaded from the same government website (data.vic.gov.au) with the same ...
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502 views

QGIS : How to add points from GPS stream data

I try to place points on QGIS using the GPS plugin but it does not like me. GPS stream is good, I have the read on the data on port com 66, QGIS seems to be good with it since it locates correctly ...
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223 views

How to export training area information?

I did a supervised classification of a whole Landsat 8 image with 700 Rois (training areas) with the Semi Automatic Classification Plugin. I want to export the class names, the coordinates and the ...
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97 views

Ignore database columns when inserting feature

I have a spatial table in MSSQL which has a "Geog" column that stores WKT and an "area" column that automatically populates based on the "Geog" geometry. This table is succesfully added in qgis and ...
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467 views

QGIS Server: how to get WMS GetLegendGraphic in HTML?

On MapServer you can get HTML content based legend graphic with WMS GetLegendGraphic. On QGIS we can have only PNGs. It would be nice to have the same behaviour on QGIS Server, with an HTML Template ...
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957 views

Custom Icon Markers in QGIS

I have a library of .bmp logos that I would like to use to symbolize points in QGIS. Does QGIS only support .svg logos?
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85 views

PostGIS and QGIS connection using queries?

I have a shapefile and a table which I import both of them to PostGIS. With pgAdminII I am able to manipulate the table, join to shapefile and calculate new fields. When I try to do that with python ...
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162 views

Different pixel values for a raster between QGIS and PostGIS

I have inserted a Landsat raster into PostGIS using the command : raster2pgsql -I -C -s 28356 -M -t 100x100 /data/LS7_20150425_B40.tif public.red | psql -d postgres -U postgres Using QGIS, I have ...
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48 views

QGIS Uploading images or files for features

I am using a QGIS 2.12 project and I would like to know if it is possible to upload files and photos for each element in a layer. The files should be stored for example in C:\myproject\files I can't ...
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279 views

Memory issue? qgis python processing does not complete

I have a simple process to make some edits to all the contour files in a directory. It runs fine on the test of 100 odd files but in a directory with about 500 it stops after about 120 files. Is ...
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183 views

GDAL error in QGIS application displaying VRT files

I am working with a standalone app build with QGIS 2.8.1 on a CentOs7 machine. I got a new DTED data set which raises errors "somewhere" in the app. The app doesn't read the .dt? files directly, but ...
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79 views

Arrows plugin returning Python error

I'm trying to run the Arrows plugin on QGIS 2.10 (Win 8.1), but I'm getting an error message: Traceback (most recent call last): File "C:/.../.qgis2/python/plugins\arrows\arrows.py", line 79, ...
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208 views

different results :Slope analysis in qgis vs ArcMap

I want to make slope analysis on geoTiff. I am using ArcMap and qgis. But i get different results, but both are in degrees. I ArcMap i recive range from 0 to 42 degrees, but i qgis it from 0 to 17 ...
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77 views

Georeferencing two images at same time in QGIS?

Has anyone ever tried to georeference two images at the same time on QGIS? In my application I don't atually care much about the positioning itself, but in the scale and orientation. I have ...
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452 views

Would a QGIS qt5 build use qt5's OpenGL rendering capabilities?

Related to this question, I am considering building QGIS with qt5 (caveats acknowledged) in order to improve rendering speed with qt5's OpenGL support. Before I attempt this I need to know whether ...
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457 views

reading raster without making QGIS apply the scale factor to the raster

Since QGIS multiplies the image with the scale factor when reading, it messes up the image if the scale factor is not properly defined to the data as QGIS expected. For example, I am reading MODIS ...
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33 views

Projected CRS interfering with Spatial Analyses?

I am working with two polygon shapefiles, one of which is a buffer around the other, and a point shapefile in a project set to EPSG:54016. All layers are correctly reprojected and in the same CRS, OTF ...
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66 views

Visually clipping a search area (MCE) (QGIS)

I have some search areas to refine using a variety of vector inputs. I can clip these to get my end product but it is a messy process. Is it possible to use blending modes to visually "knock out" ...
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116 views

Up-to date agricultural land use

I'm looking for data on commodities (corn and potato). Tools such as USDA's cropscape (http://nassgeodata.gmu.edu/CropScape/) are great but lack global cover. I found this dataset http://www....
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525 views

Merge raster layers error

Is there an issue with the SAGA-tool "Mosaicking rasters"? I tried it with different rasters. In Sage itself it works fine. Algorithmus Mosaick raster layers startet... io_gdal 0 -TRANSFORM -...
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115 views

QGIS version migration of Styled Layer Files

I have a stand alone application which reads SLD files, to draw something on a map canvas (development started under QGIS version 2.0.1). Unfortunally I have to deal with these old SLD files version ...
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152 views

Spatial segregation from a raster of racial distribution in the USA

I am trying to measure the degree of racial segregation at some geographic level (let's say the county level, for simplicity) in the USA. I have a shapefile with these geographic units. To do so, I'...
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124 views

Snapping feature nodes doesn't work after feature creation (filter involved)

I've experienced a strange behaviour during editing mode: I have set a filter to 2 features (polygons), part of on of my PostGIS layers: "name"='A' OR "name"='B' After that I have created a new ...
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74 views

QGIS File Geodatabase Vertices missing

I am adding Data from a File Geodatabase to QGIS. Everything is working fine, but the drawing of a specific Line subtyp (first image). It looks like, QGIS can not draw the circle properly. An export ...
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255 views

Use QGIS and Qt dialog forms

I have a QGIS project where there are plots with a attributes like name of the owner, address of the owner, cultivate, and so on. This plots are read from a PostGIS database. The future users of this ...
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40 views

Display graduated QGIS buggy?

I counted points in polygons in PostGIS like this UPDATE hexagons SET count = (SELECT count(*) FROM points WHERE ST_Within(points.geom, hexagons.geom)); That came back with that UPDATE 1554 That ...
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890 views

Downsampling then upsampling raster using QGIS?

I'm trying to downsample a raster then upsample it again. I am using the gdalwarp function in QGIS. When downsampling the raster looks OK in the front end, I set the cell size to 10x the original ...
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377 views

How to split polygon with multiple points in QGIS?

I am working on spliting a polygon which includes multiple points. I tried it manually but due to the large dataset it is very time consuming. Are there any automated tools or plugins to do that? ...
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126 views

Merging SHP lines with attribute data combined?

I have one shapefile which contains hiking routes and another shapefile which has ski routes. Sometimes they follow the exact same path. In QGIS if the lines mentioned above are in the same SHP I ...
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93 views

r.* commands not found

I'm very new to GIS and have recently installed QGIS on my mac desktop computer, running Yosemite 10.10. I'm working with DEM data for stream network extraction, but the majority of grass raster ...
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198 views

pyqgis - refreshing only QgsMapCanvasItems not the entire QgsMapCanvas

I have a fairly complex map, consisting of many layers, and despite they're optimized, they still take a certain time to refresh. I also have a QgsMapCanvasItem representing my position, which i would ...
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53 views

Generating a plot by varying the buffer around each point

I want to create a plot like this: Basically, I have a bunch of points (properties), some of which have (and some of which don't) have Property X (e.g., a fence). I want to find out how the average ...
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315 views

apply gdal to calculate raster that is already in qgis raster calculator

I am using the following code in qgis to calculate some raster.It is not giving the correct result as it is in arcpy.I want to apply same in gdal.Can anyone help me how to use the gdal api.Please give ...
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153 views

Overlay polygons on raster in different projections

I'm overlaying polygons on a raster to get the average value inside the polygon (using SAGA->Shapes-Grid->Add grid values to shapes in the QGIS Processing Toolbox), using a geographic and a ...
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539 views

Splitting lines at a specified distance and add attribute

I have used QChainage to create points along a line every meter. What I am ultimately looking for, is to split the line layer along this point into segments with the chainage distance as an attribute. ...
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506 views

QGIS expression: select from <layer> possible?

I have a project file with many nested layers and would like to query certain layers without having to click on them first. The expression tool however requires me to select the layer I want to query. ...
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156 views

Error in my buffer plugin

In my buffer plugin, i tried the following code # Get buffer distance and selected city dist = float( myLineEdit.text() ) city = myComboBo.currentText() # Get the feature corresponding to the ...
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153 views

How to project the geographic grid in a shapefile in QGIS

Is it possible to automatically project the geographic grid (View -> Decorations -> Grid) into a shapefile layer in QGIS?
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51 views

How to georectify a fictive earth to a projection-less version

I have a picture of a fictive earth-like world. Now I would like to draw the outlines and then georectify this to a projection-less version. I really need the map unrectified. Because I want to ...
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110 views

Query does not work on joined file

Using QGIS 2.6.1 Brighton on an IMac (10.8.5). QGIS 1.8 Lisboa with exactly the same two vector shapefiles and the same CSV file works. I joined the file containing the polygons showing the features ...
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233 views

QGIS Mac OSX version cannot batch write output files after rasterization

I have been trying to batch rasterize a series of .shp files using QGIS for Mac OS X, and keep coming up against a strange problem. I am using the QGIS 2.6.1 user interface, rather than calling ...
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240 views

Finding census block with highest pop. value within census tract using QGIS?

In QGIS, I'm trying to plot a centroid of only the census block with the highest population within each census tract. So there should only be one point per tract- that of the block with the greatest ...