1
vote
0answers
24 views

Automating polygon mergers with python

This is the first real world python program am trying to write. I am trying to create a scrip that takes a shapefile that has n polygons with an integer formatted date (e.g. yyyymmdd or 6/24/2014 is ...
3
votes
2answers
63 views

“Levelling” elevation data coinciding with polygon?

I have a shapefile containing building geometries (polygons) and a elevation dataset. The elevation data doesn't perfectly match the buildings. I want to "flatten" the elevation data so that ...
1
vote
0answers
34 views

How to calculate the area of overlapping buffers within a single layer

I am very new to GIS, so don't know if this is EXTREMELY easy or impossible. I have GPS coordinates for stores (about 15000) for which I have created a buffer zone around each store location ...
1
vote
1answer
63 views

Is there a way to access the GeoProcessing tools in QGIS, in code

Is there a way to access the GeoProcessing tools in QGIS, in code? I want to find the Difference between two layers and make a new shapefile with the result.It can be manually done by selecting ...
0
votes
1answer
40 views

Issue clipping vector file with QGIS (geoprocessing tools)

I am trying to clip wind speed data (.shp format) to Canada's provincial boundaries (also .shp format). I am using the clip feature in vector > geoprocessing tools. For some reason the function always ...
1
vote
2answers
52 views

Create Shapefile of all overlapping features from single Shapefile

I need to create a Shapefile out of another Spahefile that consists all overlaps of features within the initial Shapefile. I'm sure there is a simple solution using ArcMap or QGIS, but at the moment ...
0
votes
1answer
147 views

How to enable multithreaded processing in qgis 2.2

I have found multiple links that appear to say that this now exists in qgis 2.2, but it appears that it's only using one core to full capacity. This is running on Ubuntu 14.04 The current process is ...
3
votes
2answers
146 views

Split Lines at Intersection of Other Lines

I have two line layers (roads and contours in this example) and I would like to split the roads layer every time it crosses/intersects a feature on the contour layer. I can't seem to find a tool that ...
0
votes
0answers
55 views

Finding shortest cumulative route (i.e. best 'hub') between networked points

How do I find the shortest cumulative route (i.e. best 'hub') between networked points? I have a dataset where some but not all of the points in the network connect to each other, however it is ...
1
vote
1answer
73 views

Finding the common borders between polygons in the same shapefile

The question is essentially the same as here, except that I want to do it in qgis. Thus, is there a qgis function equivalent to the ArcMap intersect function that will take a polygon layer and output ...
1
vote
0answers
73 views

Is there a decent algorithm in QGIS Process Modeller to create a grid?

I am using Process Modeller to automate merging several vector layers and then creating a grid to cover the extent of the merged layer. There are functions which already exist which are not listed in ...
0
votes
1answer
85 views

Problems running model in QGIS

I am trying to make a batch model to convert band 2 and band 1 MODIS 8 day composites into NDVI. The input files are in tif format, but I want the output to be saved in Idrisi .rst format. I am ...
2
votes
0answers
46 views

how to assign unique attribute value per neighborhood? [duplicate]

I have a feature class of adjacent polygons and I want to assign an integer attribute value to my polygons based on the following rules : a polygon must not have the same attribute value than any of ...
8
votes
1answer
257 views

Where is this raster offset being introduced in the QGIS processing toolbox?

I'm using the (awesome!) processing toolbox in QGIS 2.0 to reclassify some NoData values in a raster from -9999 to 0, but at some point in the process there's an offset of about 0.2 degrees being ...
2
votes
2answers
261 views

Calculating elevation profile of a trail?

What would be the best way to calculate an elevation profile of a trail remotely (without using altimeter/gps tracking your steps)? For example, to do it in the most rudimentary way you might take a ...
1
vote
1answer
48 views

How to get estimates of areas of overlapping polygons in one shp to another?

Sorry for my ineptitude, but I have two vector shape files of Africa. One has polygons of countries, and one has polygons of tribes a long time ago. What I want to do is to find the intersection of ...
0
votes
0answers
59 views

what happens to attribute table while performing union, intersection, difference of gml and shp file in QGIS

I am trying to do an analysis of the data conversion from shapefile to GML file using QGIS. For the analysis I have taken a point, line and polygon file. I first took a shapefile and converted it into ...
4
votes
1answer
407 views

What is the distinction between Difference and Clip in QGIS?

What is the primary distinction between the Difference and Clip geoprocessing tools in QGIS?
2
votes
1answer
81 views

Raster layer calculator

In PCI Geomatic, I have two raster layer.raster1 identified like %1 and raster2 like %2. if (%1 <= 10) then %2 = 60 elseif (%1 > 10 and %1 <=50) then %2=80 elseif (%1 > 50 and %1 ...
1
vote
2answers
107 views

geoprocessing across multiple vector layers QGIS2

I have 6 layers of point data (each layer is one year), where data in each layer are distributed throughout a grid, and the grid is identical in each layer. I'd like to extract data from each layer, ...
4
votes
4answers
214 views

How to convert result of dissolved buffer into individual polygons?

I am wondering if there is a way to easily split results of a disolved buffer into individual polygons? E.g in the screenshot below all of these buffers are one item, can I split them into individual ...
1
vote
0answers
25 views

How to make gdalbuildvrt available in processing modeller?

I would like to make a model in QGIS that builds a virtualraster from several raster files. Unfortunately the gdal function is not available on the modeller. So, my question is: how to make this ...
2
votes
2answers
296 views

What is faster for geoprocessing (intersect) big shapefiles?

I have 200 Mb shapefiles of polylines downloaded from OSM. I've been working with QGIS 2.0 in Ubuntu 64 Bit 8 Gb RAM to make some geoprocessing tasks and it's taking 2 days for processing. Once I've ...
5
votes
1answer
528 views

Split polylines at polygon boundaries in QGIS

I have a set of contour lines and a polygon set containing glaciers. Because I want the glaciers to have blue contours, I need to split the contour lines at the glacier boundaries. I can achieve this ...
1
vote
1answer
72 views

Counting and sum by two layers

I´ve got to layers, both polygons. Layer 1 consists of propertiers, where ID is individually names. Layer 2 consists of lakes. The query I want is: Total count of squaremeters of lakes for each ...
0
votes
1answer
291 views

How to use SEXTANTE in a script outside QGIS?

I´m trying to do some geoprocessing using the QGIS Sextante plugin outside of the QGIS application (and integrate it with different other libraries like arcpy, etc.). import sys, os from PyQt4.QtGui ...
0
votes
0answers
52 views

Getting the active projection Qgis uses on the fly

I wan't to get the correct length of a feature in python and there is no problem getting it from the database and transform it ( *SELECT ST_length(ST_Transform(geom, 3007))* ), but how do I know which ...
1
vote
1answer
91 views

Add buffer only on one specific side of polygons

I have a shapefile with multipart geometry (multipolygons), namely communities (blue on the picture below). There are also lakes (white), but for these I don't have a geometry, they're just "empty". ...
0
votes
0answers
132 views

Point in polygon analysis fails with “TypeError: arguments did not match any overloaded call”

I am using QGIS 1.8 on Windows 7 I want to perform a point in polygon analysis using the Vector > Analysis Tools menu. My point layer is the result of a SpatiaLite query which returns 10'000 points. ...
3
votes
0answers
155 views

How to create a line layer which connects a point layer to a line layer?

In the map shown below, I have manually created the dummy lines (in green). Using python, and without using PostGIS or sextante, I would like to automate the creation of these dummy links between a ...
9
votes
2answers
388 views

Can I add an ArcToolbox tool to QGIS?

I have been using a publicly available tool in ArcGIS called SPreAD-GIS. It is a series of python scripts that are "implemented as an ArcGIS toolbox" (with tbx file). I am new to QGIS. Is there a ...
1
vote
0answers
332 views

How to calculate weighted mean coordinates within polygons?

I'm using QGIS 1.8 on OSX 10.8.3. I have a polygon shapefile of all of the US state legislative districts. I also have a layer of points that are centroids of US Census Tracts, with a field for the ...
2
votes
0answers
148 views

How to use Memory layers in QGIS plugin to store results of Geoprocessing tools

I'm building a plugin to perform Multi Criteria Analysis (yes another one...). As part of my workflow intersecting vectorlayers is needed. I use QgsOverlayAnalyzer.intersection (a pity union is not ...
1
vote
1answer
197 views

How to set tolerance value of Geoprocessing tool in QGIS?

Is it possible to set tolerance value of geoprocessing tool on QGIS. History is below. There are two polygon which have to be the same position. so, I set topological rule "A must covered by B" on ...
1
vote
4answers
448 views

How to create internal polygon without overlap on QGIS1.8.0

I would like to create new polygon inside the existing polygon. It does not means donuts polygon. I would like to have two polygon without overlapping. I can create if I don't check "Avoid ...
3
votes
1answer
347 views

Calculate number of people within 50 km of a point

I have two data sets: World population (raster) in EPSG:4326, from http://sedac.ciesin.columbia.edu/data/set/gpw-v3-population-density-future-estimates/data-download A shp file with points ...
9
votes
3answers
728 views

How to sum up values of neighbouring polygons?

I hope that you can help me with the following problem: I have a vector (polygon) layer. I would like to add an attribute to the layer that - for every polygon - sums the values of a specific field of ...
6
votes
1answer
645 views

How to calculate te area between contour lines on a DEM with Qgis 1.8?

Does anyone know how to calculate the area in km² for each altitudinal band (between 100 and 200, 200 and 300...) based on a DEM? I added the contour lines with a distance of 100 metres but could not ...
6
votes
1answer
256 views

Simulate (Mock) GPS Tracks

I have the following scenario: 1) I need to create GPX files for use in testing of a mobile device. 2) The tracks to be described within will span large distances over long time periods (i.e. it's ...
0
votes
1answer
406 views

table of polygon centroids

Given a polygon layer, census tracts, how can I generate a table of centroid coordinates in QGIS, or add columns with the centroid coordinates or generate a new layer of polygon centroid points?
4
votes
3answers
785 views

How to split features?

I would like to split a shapefile in qgis according to how the polygons overlaps. Don't know how to though? See pic for explanation:
2
votes
2answers
179 views

Determine the furthest driving distance from a road layer to the nearest point of a point layer using OSM/QGIS

In a specific geographic area, I have a road layer and roughly 30 points dispersed around the geographic area as part of a point layer. Both layers are in SHP and PostGIS formats. The records from the ...
4
votes
1answer
2k views

Performing Geoprocessing SQL Queries in QGIS from a PostGIS Database

This may be a dumb question, but is there way to run a PostGIS geoprocessing SQL query in QGIS? Specifically, I am thinking of running SQLs such as ST_Union, ST_Split etc etc. I have tried the ...
9
votes
3answers
3k views

Divide a complex shape file into a grid

I have a decently detailed shapefile with polygon/multipolygon features (the file is about 500mb). It's actually a shapefile of the entire world, with the features representing coastlines. I need to ...
4
votes
1answer
2k views

How to get point attribute from polygon layer?

I have two layer, one (A) has point features and the other (B) has polygons. I need to produce a new table with some (the ID) or all the fields from the A table and some (the area code) or all from ...
5
votes
1answer
384 views

How to divide a polyline by intersecting isochrones

I have two shapefiles, the first representing a path (a polyline with a single category), the second representing isochrons from the same origin (point 0) which intersect the above mentioned path. I ...
20
votes
4answers
3k views

Is there any model builder in QGIS or other open source GIS?

Like the ModelBuilder of ArcGIS for Desktop to run simultaneous geoprocessing tools, is there any model builder available in QGIS or any other open source GIS software?
2
votes
2answers
3k views

Can two polygon layers be merged in QGIS on a common id?

Can two polygon layers be merged in QGIS on the basis of a common id? Update: Ok , the dissolve tool works fine. But for instance lets say I have 10 polygons. 8 of them are together , so when ...
22
votes
5answers
4k views

How to identify clusters in vector point data?

I have a vector dataset of rural broadband data-points (how fast, etc.) and I'd like to explore if there are clusters of points with similar characteristics, and to plot polygons encompassing them. ...
10
votes
1answer
825 views

Is there a way to access QGIS plugins in Python?

Is there a way to access QGIS plugins in Python? I'd like to write a script to do some geoprocessing, and I'd like to use the clip, regular points and convex hull tools in fTools, as well as the Road ...