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

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NDVI Workflow Problems, Red Channel Seems High Causing Low NDVI value?

I did some searching but nothing came up around this. I'm trying to verify a workflow from images to an NDVI to verify I have a basic workflow correct. Process images example dataset through ...
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1answer
32 views

How to apply a radial fill to a voronoi polygon centred on its original home point in QGIS?

I'm working with a point layer (airports from OpenFlights), and I want to create a map of distance to the nearest airport. I thought I might be able to do this by using radial fill on the voronoi ...
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7 views

Using Lastile in Qgis

I want to tile one large las tile into few minor. But i just cant get it done. My original LAS file have around 30mil points and i want to get 5 smaller LAS files with 5mil points in it. What is ...
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2answers
68 views

How do I make equidistant circles covering the whole globe in QGIS?

What's the simplest way to make equidistant circles in PostGIS/QGIS? (my software versions are Postgres 9.3, PostGIS is 2.1, QGIS 2.10) I tried this in PostGIS, but the circles that come near or ...
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1answer
53 views

Sorting points based on Northing and Easting

I have around 1320 point/centroid features in a shapefile for my research plots. Each point/centroid has X and Y coordinate associated with them which were calculated using Field Calculator > Geometry ...
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20 views

Displaying heatmap with large number of dense points of interest in QGIS?

I am currently trying to make heatmaps of bird observations in an area. I have had a lot of success making the actual heatmaps for most birds, except the ones that are extremely abundant. I use the ...
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1answer
15 views

OTF reprojection and reprojecting layer not working in QGIS

more troubles in QGIS. I georeferenced this raster in Corrego Alegre UTM23S and loaded up, so project CRS automatically changed to that. So far so good. I need it to be however in WGS84 UTM 23S. None ...
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26 views

Qgis network analysis why find vertex return always -1

I'm trying to compute the shortest path between points using the QGIS networkanalysis library. But the graph.findVertex always return -1. Basically what I'm trying to do is : 1/ Given a set of ...
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1answer
13 views

Loop to check multiple polygons overlap in r

I have a set of polygons (available here: http://ulozto.cz/x39ELbFt/polygons-zip) created in QGis and processed in R. I would like to know if they are overlapping or not, and if yes, where is the ...
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1answer
34 views

Can't get my QGIS external map to display on Ubuntu trusty: QObject::connect: Cannot connect (null) error

I've been following along the examples from the book "Building Mapping Applications with QGIS and for the life of me I can't figure out why my shape files aren't loading and displaying in the app ...
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1answer
43 views

My QGIS plugin shows GUI but not Works. How to get Error log?

I am new to PyQgis. I made a simple calculator with PyQt4, now I am trying to run it under QGIS. I connected calculator as plugin, and tested it, its GUI works without error but it does not calculates ...
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14 views

Prevent Overlapping Features in QGIS from Being Faded

I have multiple layers in QGIS that I've set as transparent so I can see their respective features. However, I would like one layer (showing proportionally sized points) to NOT fade when it overlaps ...
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11 views

How can I extract the latitude and longitude from a s57 File [duplicate]

I had to extract the longitude and latitude from a s57 file, in order to superpose a satelite view from the same point. These coordinate will allow me to get the exact position on google map by ...
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2answers
53 views

How can I import shapefile in python?

How can I import a shapefile in python? from PyQt4.QtCore import QSettings, QTranslator, qVersion, QCoreApplication from PyQt4.QtGui import QAction, QIcon, QFileDialog # Initialize Qt resources from ...
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15 views

What solutions to use QGIS as insert tool for a Postgres relationnal database?

I have a Postgres/PostGIS relational database and I would like to use QGIS as an interface for inserting data. The thing is that my database is quite complex and I need my tool to handle the following ...
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14 views

QGIS measure growth in special directions

I want to measure the growth of different areas in special directions. The same as in this article of M.S.Moeller on page 5 (Figure 5 and 6). But I don't know how to build such a Wind Rose in Qgis. Do ...
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1answer
14 views

automated selection by attributes and location within another Layer

I have two Polygon Layers. Layer A are Districts of a City and Layer B are Blocks of a City. Currently i'm working with QGIS 2.6.1 and i don't have access to any other GIS. What i'm trying to do is: ...
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24 views

Merge layers (SAGA) ERROR

with QGIS 2.10 it is not possible to merge vector layers with the "Processing-Saga" tool (merge layers). The following error log comes up: Algorithmus Merge layers startet... shapes_tools "Merge ...
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1answer
27 views

Calculating distances across land only

I am trying to do point to point distances in QGIS but I have points to point distances that are being calculated across oceans. Given people don't generally fly around cities does anyone know a way ...
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14 views

unsupervised classification in qgis (Orfeo toolbox)

I want to run an unsupervised classification of two landsat images in qgis. Therefor I want to compute a kMeans and a SOM (self organizing maps classification). Unfortunately it doesnt work. I tried ...
2
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1answer
29 views

How to calculate the 3D length of line segment in QGIS?

I've been looking through all of the GRASS commands in the QGIS 2.10 processing toolbox and it seems like one of these must be able to do this but I haven't found one yet. There is 'v.sample' which ...
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30 views

How do you merge overlapping .asc files in QGIS with topography and bathymetry?

Firstly, apologies for any incorrect terminology - this is my first time trying to manipulate GIS data. I have two files. The first is higher resolution (SRTM) topography data for a region of islands ...
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32 views

Gravity/Huff model tools in QGIS without rasterlang plugin?

As the person of this question: Gravity/Huff model tools I am looking for a tool to simulate a gravity model using a point-based layer. As in the case there, my points have a z-value and the higher ...
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1answer
24 views

Checking if a POI is on the road

I have a list of POIs from around the world and their latlongs. I also have the database from all roads in the world. What I want to do is find the popular roads from all of these. My idea was to ...
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15 views

Need to edit info to new column for label and concatenate information which is alphanumeric

I need to end up with the following: Jones, H.L. A-345 The data is entered into Survey Name (as string). Survey Abstract #is entered as "345" I need to add "A-" to the number, and then concatenate ...
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2answers
57 views

How to create a dashed polygon border in C++?

In my maps I have a symbol, his type is polygon, I want to change the line style of the border, actually is solid , I had to put it in dash Is there a simple way to change it ? i think to the ...
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22 views

How to edit a shape which the toggle Edit buttom is noot enable in QGIS?

I just download a shape file (polyline) from internet and I would like to do some modification in the line, but the Toggle Editing buttom is not enable. It seems that the file is locked and is not ...
2
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1answer
34 views

How to find if map layer registry is empty?

In my script I want to open layer named my_layer if it is in the map layer registry. I use following code for it: inputLayer = QgsMapLayerRegistry.instance().mapLayersByName("my_layer")[0] If not ...
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48 views

How to access a deleted features attributes (before committing)

I have a signal setup for a feature deletion event on a layer: self.layer.featureDeleted.connect(self.feature_deleted) When I try and grab an attribute from the deleted feature on the slot, a ...
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1answer
20 views

How to scale SVG symbols which are not label background on zoom level in QGIS

I need to scale the SVG symbols on zoom level. @Underdarks answer in the posted question did not help me thus I can't set the SVG symbols as label background for I have labels which should not be ...
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2answers
48 views

Polygons in one layer have different attributes

Is it possible in PyQGIS to have in one layer more polygons and some would have one set of attributes and another different? E.g. Polygon_1(name, size, average_age), Polygon_2(name, size, ...
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3answers
255 views

Free printable background map: land use, rivers, etc

I am looking for a free printable background map of europe which should look more or less like the OCM landscape: land use, major rivers, coast lines Is there any WMS or raster set whiche enables me ...
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2answers
46 views

How can I create a QGIS plugin that needs an external Python library?

I’m trying to enhance QGIS's Profiletool plugin by adding DXF export functionnality. For this, I need to to import dxfwrite library. As it's installed on my computer, i added the following lines to ...
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1answer
16 views

Normalized icon for BOYLAT

I try to find normalized icons to use for the BOYLAT ( lateral buoy ) I find description, but for the boylat it seems that different shape to show different buoy link for the description ...
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1answer
17 views

Rendering of SVG for layer symbols using QGIS?

I have a little problem with the rendering of SVG for layer symbol. I want to creeate a categorized symbol to show different style of buoy I have for that two icons the first is an half circle ...
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1answer
31 views

Why do pixel (cell) values change for 32 real NDVI values when taking from Multispec to QGIS?

Landsat 5 values change from normal NDVI -1 to 1 when created in Multispec as a 32 bit signed data image. When adding the raster layer in QGIS, the value range changed to 0-255. How does one ...
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1answer
19 views

Opening MapInfo .TAB file containing text objects in QGIS?

Whenever I try to open a MapInfo .TAB file that contains text objects in QGIS, the text objects are converted to point objects. Any help, please?
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1answer
35 views

How to get PostGIS DB name from QGIS layer?

I'm writing a custom Processing script that needs to know which database connection a vector layer resides in. I can't find anywhere in the API a function to return this information from a layer. So I ...
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3answers
67 views

Grass toolbar for QGIS 2.10

I don't see the GRASS toolbar in QGIS 2.10 (Pisa). There are still GRASS commands in the Processing toolbox. I know there was some upgrade of GRASS for 2.10. Is the toolbar not available anymore? If ...
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1answer
48 views

Loading Natural Earth *.prj file into QGIS 2.10.1?

I have found solutions for this problem in other versions of QGIS, but none that apply to the newest version 2.10.1. Whenever I try to import a Natural Earth Raster projection that is a prj file I get ...
2
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1answer
47 views

How to load a style from POSTGIS in PyQt

The thing is that I have four styles I have created in QGIS through the GUI and saved into a postgresql database. I can see them in the table named layer_styles I have seen similar questions asking ...
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2answers
24 views

How to put a frame around a legend using QgsComposerLegend?

I can already see this being a simple answer but I'm stumped with this. I want to create a frame around a legend created by a PyQGIS script Code snippet is: legend = QgsComposerLegend(c) ...
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1answer
25 views

How can I check in QGIS python if an atrribute is included in my layer?

I use the following code: for field in self.layer.pendingFields(): if field.name()=='elevation': do this else: do that Although there is an elevation attribute in my layer ...
2
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1answer
33 views

what is the “clip” feature for color ramps?

In the singleband pseudocolor band rendering, there is a boolean checkbox "clip". What does this do? I don't notice a difference in my maps and haven't found documentation for it. Thanks
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62 views

Unable to stylize as pseudocolor render type

In a raster layer's Style Properties, I can choose pseudocolor render type, and choose a color ramp and classify the raster. However, when I click the 'Apply' button, or click 'OK', the ...
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1answer
21 views

Updating a column in MapInfo based on Symbology or colour

I am transferring a large dataset from MapInfo (V 12.0.2) to QGIS (V2.8.1) and I want to be able to create a column in the MapInfo attribute table that differentiates features with different ...
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17 views

Problem using EPSG:3395

in my application I use OGC:CRS83 for the coordinatereferencesystem, but now I had to change it to EPSG:3395 when I call : mQgsCoordinate->createFromOgcWmsCrs("EPSG:3395") there is nothing in ...
2
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0answers
50 views

Create Indexes Within a View? How could I Speed up Spatial Queries Over a View?

I´m trying to add a view from postgis using QGIS, what´s facile. The problem is that it´s taking too long to load it and to perform any kind of operation, for example, as simple as counting rows. It´s ...
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0answers
10 views

Unable to make qgis build in cmake

I am trying to build qgis without any change in source code which i have downloaded from github using clone and i have download OSGEO4W from qgis.org and the same is installed in c drive. I have ...
2
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1answer
25 views

QGIS: Finding electric network loops

With QGIS, how can we analyse an electrical network to find loops? Using Python is not a problem, however there is not a solution in the QGIS Python API. The QgsGraphAnalyzer has dijkstra and ...