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

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2
votes
1answer
111 views

Using TIN - interpolation plugin - to calculate volume

I am having trouble calculating the volume of my TIN. I have attempted to create a TIN using the interpolation plugin in QGIS. Here are the steps that I followed. I added a Zvariable row in the ...
2
votes
1answer
107 views

How to change parameters of certain algorithms in QGIS process modeler during run time?

I am using Process modeler to automate a bunch of things like Create Graticule -> Extract points at the graticule centeroids -> Add coordinates to the points -> update certain fields of the point file ...
4
votes
6answers
3k views

How to fix quickly a lot of geometry validity errors in QGIS?

I am working on ownership data at a US county level. I have one shapefile per county that contains thousands of tax parcels. I need to dissolve the polygons representing parcels owned by the same ...
4
votes
3answers
135 views

USA County level, detailed OpenStreetMap basemap in tiff?

Is there any way to get detailed (close zoom) OSM tiffs at the county level in the USA? I would like to use them as basemaps for a class I am teaching in GIS, using QGIS. I know about (and love) the ...
1
vote
0answers
79 views

Word cloud labels in QGIS from database

I would like to do some word clouding as labels in QGIS from a series of tables in a database. Examples of word clouds can be found here: Word Cloud - Google Search I have two tables in a database: ...
-1
votes
1answer
74 views

How to clip a raster with a mask in QGIS? [duplicate]

I am trying to clip a raster using a virtual raster as mask layer in QGIS. It doesn't create a file. Could anyone explain how I should proceed to do that?
3
votes
2answers
119 views

Show categories in QGIS

I have a .csv file pointing at coordinates. It is a large file that is edited often. In it, I have three groups of data (say A, B, and C). Within each group there are a number of Names, and each ...
1
vote
1answer
89 views

How can I fix a broken gdal-tools plugin in QGIS?

I have QGIS installed on my 2011 macbook pro and I recently upgraded my OS to 10.9. After the upgrade, I noticed that QGIS gives me this error (see attachment 1) saying that the plugin is not ...
1
vote
0answers
28 views

Problem Loading Plug-Ins in QGIS 2.2 on Mac

I'm trying to load the 'processing' module in QGIS (2.2.0-Valmiera on Mac OSX 10.8). However, this module and others (e.g. GarminaCustomMap) re failing to load with a message: ImportError: No ...
1
vote
1answer
1k views

qgis polygonize error 4 “file does not exist in the file system”

When I try to convert a raster DEM (in asc or geotif format) to polygons I get the error below. ERROR 4: `Y:/GIS/oversvmmelser/tmp/out.tif' does not exist in the file system, and is not recognised ...
5
votes
1answer
247 views

Simplified flood “model” / estimation from elevation data

The goal is to present an estimation of potential flooded area. But still keeping it simple. I know this will not be accurate. The question is: will it be good enough for at gestimate / rough ...
1
vote
0answers
210 views

How to enable Map Tip display text in qgis and qgiscloud?

I'm using the free version of qgiscloud and qgis 2.4. I noticed that if I'll use the HTML option in "Map Tip display text", the map in qgiscloud will only show the title of the layer when I ...
3
votes
0answers
146 views

Create vector grid from canvas using script

I've modified "Hex grid from layer bounds" script to my need. Just added cellsizex and cellsizey. Changed the hexagonal - 3 to "1" to make it as a square grid. Is it possible to include an option to ...
3
votes
0answers
203 views

ISOdata classifier in QGIS?

Is there a function that produces an ISODATA unsupervised classification in QGIS? The only unsupervised classification function I can find is a KMeans.
2
votes
0answers
28 views

QGIS is locking the clipboard from other application? (SitesPlus)

We are starting to use QGIS along with Sales Forecasting software Sites Plus by Gravitec. An ugly problem just popped up: Whenever QGIS is open, any attempts to calculate a data table in SitesPlus ...
6
votes
1answer
371 views

Interactively determining upslope and downslope areas on DEM?

I know SAGA GIS can be used to interactively generate maps of upslope and downslope areas for a cell within a DEM, but the output is pretty ugly. An upslope area is defined as all cells (for a ...
0
votes
0answers
182 views

How to save a WMS layer at multiple resolutions as .tif using pyqgis

How can I export a wms-map-extent as a .tif from QGIS? Is it possible to call the "Save as.." function of a WMS-raster-layer from pyqgis? (E.g. by simulating right-clicking the layer, choosing "Save ...
2
votes
1answer
229 views

QGIS show gdal_polygonized file in EPSG:54004 instead of EPSG:3857

I am polygonizing a TIFF with the gdal_polygonize.py and the resulting Shape is shown in QGIS in the wrong projection - EPSG:54004 instead of EPSG:3857. I have a TIFF in EPSG:3857 and polygonize it ...
3
votes
1answer
114 views

Calculating distances from points to the centre of cells

I am using QGIS 1.8.0 (using older version because I need the Qmarxan plugin which is not available for 2.4.0). I have a study area that has a vector laying of "planning units", or cells over the top ...
2
votes
1answer
113 views

How to use inbuilt tools in QGIS Modeler?

Is it possible to incorporate inbuilt tools like, for eg: vector grid of Research tools in QGIS model builder ?
2
votes
1answer
306 views

What's wrong with my expression to control label colors?

I am struggling to alter the label colours according to field values (as strings) in the attributes table. In my mind what I want is: If the string in column X = 'Proposed' Then label the point ...
2
votes
0answers
196 views

How to develop a real-time navigation App using QGIS API?

I want to develop a navigation application based on QGIS using C++, for live tracking. I think it is quite normal for GIS to do such things, especially QGIS as it is a very mature GIS platform. But ...
4
votes
1answer
209 views

Is there an issue with Zonal Statistics calculating wrong mean values?

I tried to solve the following issue by myself but without success. On the one hand I have a raster file which is the result of the processing "shapes to grid" tool. On the other hand I have a ...
2
votes
0answers
59 views

Why does my clipped raster seem to be slightly moved?

I'm having some problems with clipping rasters. I started clipping my raster using extents, but I saw that the clipped raster is different from the original raster. I created a virtual raster to use ...
0
votes
3answers
152 views

What Open Source Packages are available to provide routing

I am looking for ways to validate mileage charged by our contractors. They are paid from a central location to a customer, and then from the customer to a drop off location. I use QGIS for a bunch ...
2
votes
1answer
229 views

Cannot load postgis layer from sql string in pyqgis

I'm trying to load a layer using the following code in qgis python console: sql = "(select the_geom, ID from mytable)" uri = QgsDataSourceURI() ...
2
votes
2answers
147 views

How can you create a depth raster from a DTM and a polygon in QGIS?

I have a DTM raster and a flood outline in polygon format - how do I create a depth raster for the flood outline (i.e. flood level minus DTM level)?
0
votes
0answers
69 views

How to reference a number variable in r.mapcalc within QGIS graphical modeler

I need to run the following formula in r.mapcalc: (xor(abs(A-B),abs(A-C))>120)*A I would like to however use a user defined number input variable instead of the 120. I already have this variable ...
3
votes
1answer
83 views

In QGIS, is it possible to save graduated styles to use on different columns? [duplicate]

I'm using QGIS to produce thematic maps of 9 quantities (given in 9 columns in the attribute table) which have values broadly within the same range and I would like to plot them using the same ...
2
votes
2answers
98 views

kml does not overlay correctly in QGIS

In QGIS, when I insert a kml contour that was created in Google Earth, it appears misaligned in respect to all the other layers. Note in this image how the red contour is moved upwards with respect ...
0
votes
0answers
58 views

insert row into postgis query table in QGIS

I find I am using QGIS (2.4) more and more as a client for PostGIS database tables with geometry, but also for tables without geometry, partly because it's good just to use the one application and ...
2
votes
0answers
91 views

How to design labels which look like a fraction (with a fraction line)?

I want to create labels like a fraction using data from two columns. I have tried to use: "Field" || '\n' || '――' || '\n' || "Field2" but it doesn't look good. How can I do it using other method? ...
2
votes
0answers
44 views

Creating Form in QGIS

I want to create a form for editing attributes in QGIS. I have a lot of question and hope somebody can suggest how they work or where I can read about the next elements of form: Classification List ...
1
vote
0answers
124 views

How to create a svg item onto Map Canvas in QGIS API?

I'm working on a project with QGIS-2.4.0 API using C++. I need to load some svg files to the application for displaying as symbols. QGIS API has a class named QgsMapCanvasItem, which is an abstract ...
2
votes
1answer
331 views

Setting up QGIS Server at low cost for small user community?

I want to setup QGIS Server at a low cost for a small user community (mainly me). Parameters: Some data is private so something like qgis cloud not an option (not enough money for paid option). ...
1
vote
1answer
103 views

How to use bold text in QGIS font marker symbol?

Is it possible to use bold text with the Font marker symbol in a QGIS (point) layer?
1
vote
2answers
178 views

How to style graduated using size-scale field

Is it possible to style based on size-scale field using graduated symbol but instead of using color ramp, I would like to display its size. I would also like to display this in the legend in the map ...
3
votes
1answer
260 views

Dark Object Subtraction QGIS

I'm trying to do Dark Object Subtraction (DOS) for a Spot2 and 4. I have calculated the TOA reflectance and now want to get the at surface reflectance. Using QGIS I would like to know how I can do ...
1
vote
1answer
331 views

What's the reason for this Invalid Layer “Cannot open GDAL dataset …” error

When adding a rasterfile with QGIS python console there appears an error when the first letter of a rasterfile to be added is not written in capital letters. Why this behaviour? Example case1: ...
3
votes
1answer
41 views

How to store a password during one QGIS work session?

I'd like to get into qgis-plugin development, but am rather new to both python and QGIS development. I intend to write a plugin which connects data from a mysql database to shapefiles. As the data is ...
3
votes
2answers
54 views

QGIS doesn't create the correct projections when creating new shp files

I received shapefiles exported from ArcGIS with EPSG:2227 as the CRS, which should be: +proj=lcc +lat_1=38.43333333333333 +lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5 +x_0=2000000.0001016 ...
9
votes
0answers
164 views

How do ESRI and QGIS calculate scale values of geographic projections? [closed]

Does anyone know how (from which location) scale values are calculated in ESRI products and QGIS for geographic projections? The only thing I've noticed is that QGIS is changing scales when you pan ...
3
votes
2answers
749 views

How to calculate the square root of a feature attribute?

I have a polygon shapefile with over 16k features. Each has an attribute (Double, Precision(10) Scale (2)) that I am trying to calculate the square root of, and store in new field. Is there a tool, ...
1
vote
0answers
36 views

Can HTML annotations be autogenerated for each location in QGIS 2.4

Can HTML Annotation Boxes be autogenerated on the whole map, linked to locations, and always have the same html file loaded for all of them?
1
vote
2answers
117 views

Creating counties in QGIS

I have a raster map (a photocopy I took from an Atlas), and a vector map of the UK. The raster map shows pre-1890 Scottish county borders. I have geocoded the map so that the raster borders overlap ...
1
vote
1answer
237 views

Reprojected Shapefile does not align with Openlayers Plugin [closed]

I am based in NSW, Australia. I have a shapefile that when I underlay with the openlayer plugin (google satellite), the shapefile is skewed despite all my efforts to correct it. I changed the ...
0
votes
0answers
20 views

unable to open the QGIS Tab

I have download the QGIS Softarwe of “gis-osgeo4w-1.7.3-00624b3” and “QGIS-OSGeo4W-1.8.0-2-Setup” both from net and installed both in my system, My system is running window07 professional Service ...
1
vote
0answers
21 views

QGIS Equivalent of MapInfo's 'Combine Objects using Column' [duplicate]

MapInfo has a function that takes a table, and creates a new table populated combines them by a specified value. So, combining on the name field, and specifying that the Area field should be ...
3
votes
1answer
325 views

Adding an “m” to the end of every number in a row

What function do i need to use to add an space and an m after every item in a row, using the field calculator in the attributes table. I have a load of numbers (as strings) and would like to add m ...
0
votes
0answers
162 views

Splitting existing polygons with existing polylines(roads) with GME tool “split polygon by lines”

After reading through many of these articles i believe the GME tool "split polygon by lines" should be useful to my problem. I have a polygon that needs to be split by a road layer. When i run this ...