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

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5
votes
2answers
2k views

How to set the value of a pixel based on its current value?

I am attempting to set the value of a pixel based on its current value. I am using the Raster Calculator in Quantum GIS dev 1.7 trunk. For example, if the value is 0, I want to set it to 255. Based ...
3
votes
1answer
1k views

How to Buffer with intersections in QGIS

I am buffering a layer of facilities (points). I will then use the buffer to clip and intersect another layer, containing resources. I want to answer the question, how much of the resource lies ...
5
votes
1answer
413 views

Extract many or clustered cells attributes around points

My question is similar to Extract raster values at points, but perhaps more complex. How to extract the attributes of clustered cells around a point/points? For example, I have many vegetation plots ...
14
votes
6answers
4k views

Generate points that lie inside polygon

I have polygon feature and want to be able to generate points inside it. I need this for one classification task. Generating random points until one is inside the polygon wouldn't work because it's ...
4
votes
3answers
1k views

Advice on using CityGML data and GIS

I'm looking for advice on how best to use the CityGML data-structure and GIS (preferably ArcGIS/QGIS). I've read through their website and wiki and saw a list of software here that can be used to view ...
14
votes
4answers
6k views

Join non-spatial CSV to spatial data in QGIS

I have a csv which has postcode data in a field, but it is non-spatial e.g. no Easting and Northing. I have a shapefile with postcode in a field and some additional data. I want to join the csv with ...
3
votes
3answers
839 views

How to label features in QGIS using SQL statement?

In QGIS, I can't seem to find a way to define the features that I want to label using a SQL query? Is this possible? For example, I downloaded the OSM Natural shapefiles, and a lot of those features ...
4
votes
3answers
868 views

In Qgis, Is it possible to edit the datasource of a Postgis layer?

After creating a layer with RT_SQL_Layer plugin, I want to change some details in the query. Is it possible? or I have to aways create a new layer every time I want to change something in the query? ...
2
votes
3answers
483 views

Why is this polygon “self intersected” and invalid?

I have a polygon defined as follows: segment from 43:29:02 N 003:50:39 E to 43:34:12 N 003:43:04 E arc(CW): center (43:34:49 N 003:58:16 E) from 43:34:12 N 003:43:04 E to 43:45:45 N 003:59:56 E ...
2
votes
1answer
447 views

QGIS Fetch Python Plugins Crash

I am using QGIS v1.6 on Ubuntu 10.10. When I use the Fetch Python Plugins menu item QGIS crashes. If I run from the terminal with sudo I get the following error: Segmentation Fault Does anyone know ...
5
votes
3answers
1k views

Is it possible to create 3D dxf with OGR?

Does anyone know if it's possible to create a 3D dxf with OGR. I would like to assign our contour lines a z value and export them to dxf for some cad work. PS I know FME can do this, however I would ...
8
votes
1answer
634 views

QGIS- “On the fly” projection ON by default?

In QGIS 1.6, can users set "on the fly projection" to be checked ON by default (at application launch)? I know how to turn it on, but some users find they use it more often than not, and would like ...
10
votes
2answers
2k views

How do you display related records in QGIS?

Coming from an esri background I have always used relationship classes in a gdb to display records related to a feature. Eg. Relate 1 survey point to many documents, photos etc. Does any one know how ...
5
votes
2answers
478 views

Distribute points respect to features using Quantum Gis

I want to know if there is any tool to make points with respect to selected features in a theme? Using: vector, investigating tools, regular points you can do it but not with respect to a selected ...
6
votes
2answers
1k views

Support for PostgreSQL / PostGIS Inherited Tables in MapInfo/QGIS

Does anyone know if MapInfo and QGIS will support inheritance in a PostgreSQL/PostGIS database? I would like to make use of inheritance but need to make sure the software I use will work with them. ...
11
votes
2answers
4k views

How to use label classes, expressions, and annotations?

I've always found that when it comes to python, vector analysis, QGIS gives ArcGIS a run for its money, hell some of the qgis plugins exceed ArcGIS's performance by a few hours; however, I always have ...
7
votes
3answers
3k views

How To Convert A Set of ARC/Info ASCII .e00, .e01, .e02, etc Files Into .shp Files

I have a set files that I downloaded with extensions (.e00, .e01, .e02, etc). I have read that these are files used by ARC Info mainly, but I do not have ARC and nor am I really that interested in ...
8
votes
2answers
848 views

Are there any tools / plugins to develop mapbooks using QGIS?

Are there any tools / plugins to develop mapbooks using QGIS?
14
votes
3answers
1k views

Rubber sheeting in GRASS or QGIS

We are in the process of getting our property boundaries corrected and a side effect of this is that we need to move any assets that have been drawn relative to the property boundaries, so they are ...
4
votes
1answer
637 views

esri pgdb in qgis

Using osgeo4w 1.5, when I go to add vector layer and select file type, navigate to my esri pgdb. I get a not a valid or recognized data source. If I use the database type I get a page that defaults ...
9
votes
2answers
2k views

Derive WGS84 Longitude & Latitude from British Northings & Eastings

I'm looking for a fairly simple way to append columns with WGS84 longitude and latitude to a table containing northings and eastings. The source data is Ordnance Survey's CodePoint Open, which I is ...
3
votes
3answers
294 views

Trouble getting metacarta to work with qgis?

I have a basic issue with getting qgis to accept the metacarta wms service and wonder if anyone can guide me. I add the "basic layers" to the map, but still can't see the tiles there when I go to the ...
12
votes
4answers
3k views

Shaded relief from DEM in GRASS and QGIS

I have been trying to get a good looking shaded relief model out of GRASS and Qgis for a day or so now and just can't seem to get it. The biggest problem I'm having is the valleys look like ...
9
votes
2answers
3k views

How to control Image Output Settings in QGIS?

I am exporting a QGIS map to an image format. I would like to have control over the output settings of the image (dpi), as currently it is only exporting the images at 96 dpi. Does anyone know if this ...
7
votes
6answers
3k views

Extract boundary from detailed layer in ArcGIS or QGIS

Is it possible to return the boundary (outside) permiter of a polygon layer? Let's say you have the map of the USA, for simplicity, broken down to the county level, is it possible to return the ...
37
votes
11answers
5k views

Where can I find QGIS tutorials and resources?

After several recommendations, I thought I'd familiarize myself with the capabilities of QGIS. I downloaded the program, but apart from basic loading of data, I got lost (the help file wasn't much ...
4
votes
2answers
466 views

Misalignment when generating centroids with Qgis

I was wondering if anyone could shed a light on why this behavior is happening in QGIS ? I'm pretty confident that the issue here is not due to "centroids within polygon" Edit Added a detailed ...
3
votes
1answer
412 views

Is QGIS compatible with PostgreSQL 8.4 Advanced enterprise DB with Oracle compatibility?

Sorry for such a long question. We are trialling EnterpriseDB Postgres Plus Advanced Server 8.4 with Oracle compatibility and PostGIS 1.5.1. I can create a connection to the database in qgis and the ...
8
votes
1answer
1k views

Tiled Map Services from Geowebcache in QGIS?

Can QGIS consume Tile Map Services from GeoWebCache? I know there is a article on the QGIS website which states that it does support tiled map services but it lists Tile Cache from Meta Carta labs ...
5
votes
1answer
602 views

Altering composer label items in QGIS with Python

I'm only new to QGIS and Python so this may exists already, and hopefully be easy to do. What I'm hoping to do sometime in the future is build a map book generator using QGIS as the base. In order ...
4
votes
2answers
4k views

How do you Turn on the Grass plugin in Quantum GIS?

I downloaded and installed Quantum GIS 1.5.0 with Grass using the OSGeo4W installer on my XP machine. Unfortunately, when I go to Plugins>Manage Plugins I cannot find the Grass plugin. When I browse ...
3
votes
1answer
1k views

How to clear python console in QGIS?

After running several hundred lines of commands (and getting their subsequent error statements...), it is nice to be able to clear out the console window and start clean. In the Python Console ...
5
votes
2answers
2k views

Using Qgis API and python, how can I return latitude and longitude of a point?

I have a point layer, that I'd like to return the Longitude, latitude using the qgis api. I assume I need to use QgsPoint
4
votes
3answers
2k views

What is the easiest way to measure a polyline using either QGIS or ArcGIS

I've collected a bunch of GPS polylines (WGS84). What is the easiest way to measure the length of these lines in KM?
5
votes
4answers
3k views

Quantum GIS and ECW images?

How might I enable Quantum GIS to read ECW imagery? At the moment I'm mostly concerned about this on Ubuntu 10.4 amd64, but I also use WinXP & Win7.
6
votes
1answer
643 views

How to read/write from/to QGIS project file using Python?

I'd like to save the project-dependent configuration of my Python plugin inside the QGIS project file. Is this possible and what are best practices to do so?
6
votes
1answer
1k views

How to toggle layer visibility in QGIS using Python?

How can I toggle layer visibility in QGIS via Python API?
5
votes
1answer
2k views

How to use QGIS to fix an invalid geometry without it telling me I'm not allowed?

I have a shapefile, and it's got a self-intersecting geometry in it. I'd like to fix the self-intersection, but it will require a few moves. When I attempt to move a point using the QGIS edit tools, I ...
7
votes
3answers
580 views

How to get a list of adjacent lots to a road in ArcMAP and PostGIS/QGIS?

In the following map, I have: A line / road layer A parcel / lot layer The Task: Find and count the list of lots adjacent to the road with their types (parcel_type is a field in the parcel ...
1
vote
1answer
813 views

psycopg2 error with QGIS 1.5

So I just installed QGIS 1.5 using the windows installer not the osgeo4w one and now any plugins that need access to PostgreSQL databases don't seem to work, they all throw a: "Couldn't import Python ...
3
votes
3answers
2k views

Writing a plugin for Qgis using python to access PostGIS and write geometries

Sorry about the strange title didn't really know how to word it. I currently use MapInfo to do most of my GIS work however I have recently installed PostGIS 1.5 and am really liking it so far. A ...
45
votes
4answers
16k views

How to build effective heat-maps?

Using ArcGIS, QuantumGIS, Grass, and/or GVSIG What are some of the tools and processes involved in building effective heat maps? What are the plugins involved? What are the major data requirements? ...
11
votes
5answers
4k views

Is it possible to connect to ArcSDE using QuantumGIS?

Is anyone aware of any plugins, or any other way to connect and view data from an ArcSDE database in Quantum GIS desktop?