One type of data used in GIS is geotagged photos, i.e., photos whose metadata includes the coordinates of the location where the photo was taken. But there are not many tools for working with such photos in QGIS: all that comes to mind are eVis, photo2shape and its little-known ideological parent, ImagesToShape. In principle, these two modules are sufficient for many tasks. You can use photo2shape to map the locations of photos and use eVis to view geotagged photos and link them or other documents to features of a vector layer. Sooner or later, however, a task will arise for which the capabilities of the existing tools are not sufficient.
Geotag and Import Photos is a new QGIS plugin developed for NaturalGIS. It allows you to process geotagged photos, geotag them and create a point shapefile from them.
Key features:
batch geotagging photos using a point shapefile or manually defined coordinates
add custom tags and/or modify existing tags in batch mode
create a point shapefile with a fully customisable list of attributes from a set of geotagged photos
Today, 19 July, Quantum GIS celebrates its 10th birthday. Over the years, QGIS has grown from a simple PostGIS data viewer developed by one person to a full-featured, extensible, cross-platform desktop GIS with support for multiple data formats, extensive analysis and design capabilities, which is developed by programmers from around the world and used successfully by individuals and organisations.
There is a software called TauDEM (Terrain Analysis Using Digital Elevation Models). It provides a free (GNU GPL v2) set of tools for extracting and analysing hydrological information from digital elevation models. TauDEM is developed by David Tarboton of the Water Research Laboratory at Utah State University.
The tools are written in C++, are cross-platform, and have a console interface. Users of ArcGIS 9.3.1 and 10.0 can install an add-on that allows them to run the tools from ArcToolbox using simple dialogs. For others, the only way to use TauDEM is the “scary” command line.
Recently, QGIS also got a powerful and convenient framework that allows easy integration of various tools and libraries (yes, I’m talking about SEXTANTE). Thanks to this framework, QGIS users who need hydrology tools now have a way to use TauDEM directly from QGIS.
Of course, you need to have TauDEM installed in order to use the plugin. While the installation on Windows is quite simple (there are compiled files and detailed installation instructions on the site), Linux users will have to build TauDEM themselves.
Almost a year has passed since the release of QGIS 1.7.0 “Wrocław”. It was supposed to be the last release of the 1.x branch, but time has taken its toll. The developers simply do not have enough resources to maintain several branches simultaneously, so it was decided to abandon the division into “stable” and “development” branches. All future releases will be based on the master branch. The result of these revised plans is the release of QGIS 1.8.0 “Lisboa” today.
This release contains many bug fixes and a significant number of new features. In addition, QGIS 1.8.0 has some minor API changes that affect the print composer. If you are using this part of the API in your plugin and are experiencing problems, the developers will be happy to help you adapt your code.
You can find a detailed description of the new features in the official announcement. I will only mention the most interesting ones:
QGIS Browser is both a standalone application and a dockable panel within QGIS. It simplifies navigation through the file system and connected data sources (PostGIS, WMS, WFS…), allows you to view metadata and preview data, add layers to the map using drag and drop
DB Manager is a new database management plugin. It supports PostgreSQL/PostGIS and SQLite/SpatiaLite, support for other databases can easily be added if needed. The plugin allows you to view tables (including those containing spatial information), add tables to a map or import layers from other data sources into the database, run queries, and display the results as layers
Heatmap plugin — a new core plugin for creating raster heat maps from point vector data
the functionality of the Terrain Analysis plugin has been updated and extended: in addition to calculating slope, exposure, and roughness index, the ability to create shaded and colour relief maps has been added
interface customisation tool — a dialogue that allows you to hide different parts of the QGIS interface (panels, buttons, widgets…)
reorganisation of plugins — new menus “Vector”, “Raster”, “Internet”, “Database” have been added. All core plugins and some third-party plugins have been updated and now create their own menus in the corresponding top-level menus
MSSQL Spatial support — added a new data provider to connect to Microsoft SQL Server spatial tables
support for compressed datasets — transparent opening of raster and vector data from zip/gzip archives
two new tools in the “Vector” menu: “Densify geometries” and “Create spatial index”
“Export/add geometry column” tool can perform calculations on an ellipsoid and in the layer or project CRS
Recently, there have been a lot of questions about working with CSV files in QGIS. So here is my attempt to shed some light on this complex and confusing topic. Be prepared for a longread.
We all face problems from time to time. Here are a few recent ones from my personal collection.
QGIS and SpatiaLite
Those who build QGIS themselves know that not so long ago there was a move to use external spatialindex and SpatiaLite instead of internal bundled copies. The former has been completely removed, but SpatiaLite is still there because it is either missing or too old in some distributions (namely Debian Squeeze, as well as Ubuntu Lucid, Maverick, Natty and Oneiric). The problem occurs when building QGIS with an external version of the library.
For historical reasons, the SpatiaLite can be compiled in two different ways:
as a loadable extension module for the system version of SQLite
as a standalone all-in-one library that combines the SQLite engine with the spatial capabilities of SpatiaLite
So. If you have SpatiaLite built as an all-in-one library, you can kiss SpatiaLite support in QGIS goodbye. You will not be able to create a new layer or open an existing one. What spices things up is that both configuration and compilation go smoothly: no missing files, no errors. The solution is to rebuild SpatiaLite as a loadable module and then rebuild QGIS. However, at this point you may face another problem.
SpatiaLite and dynamic linker
If the configure script constantly fails to find SQLite, GEOS and PROJ.4 when building a loadable SpatiaLite module on Linux, even though all these libraries are installed and have the correct version number, it is likely that your distribution has a policy of using unmodified source code (i.e., sources are only patched when absolutely necessary).
It should help to run configure as shown below
LDFLAGS=-ldl ./configure
PyQt4 and a new style of signal-slot connections
Since PyQt 4.5 there is a “new” style of signal-slot connection available in addition to the old style (more details). The new style is more Pythonic, and it is highly recommended to use it instead of the old style. The only thing is… if the interface was generated in Qt Designer and then converted to code using pyuic4, and the new style signal-slot connections are used in the code, then when you try to disconnect the signal from the slot, you may get a message that the operation cannot be performed. The situation has been clarified after contacting the developers:
PyQt allows connections to be made to any Python callable.
With old style connections a proxy slot is created under the covers whenever a callable is used (as opposed to when SLOT() is used to refer to a C++ slot). Therefore, in your example, a proxy is always created for the connection to Dialog.reject even though that refers to the object that wraps the C++ slot (as there is no Python reimplementation of reject()).
New style connections are a bit smarter in that they treat slot objects that refer to a wrapped C++ slot and objects that refer to some real Python code differently – a proxy is only created in the latter case.
So the rule is that if you make a connection old style then you must disconnect old style as well and the same for new style. You also need to be aware that pyuic4 uses old style connections.
It’s actually a bug, but they won’t fix it.
I accept that this is a bug, but I don’t want to fix it. The reason is that the changes required to the old style support code would be quite significant and I don’t think the risk to the stability of that code is worth it at this stage of the life of PyQt4 particularly as the workaround is straightforward.
The mentioned workaround is to create a dummy slot that simply calls the corresponding slot of the parent object. I.e., if you wanted to disconnect the reject() slot of a dialogue from the rejected() signal, using the old style, it was enough to write
Statist. My first plugin for QGIS. That was a long time ago: 2009, QGIS 1.0.0, start of discussions about including fTools in the core (yes, fTools was a regular plugin that had to be installed manually), only a few third-party plugins, and almost no instructions on how to write Python plugins… And I was younger and didn’t know much (to be fair, I still have a lot to learn).
The last major update of the plugin was also in 2009: I was happy with the functionality, and there were no critical bugs. Later, as I gained knowledge and experience, I thought about refactoring several times, but it didn’t work out. And recently, something came over me, so I sat down and did it.
Users will probably not notice any difference, as there are not that many changes visible to them: only support for getting statistics on joined fields has been added. But there are many more changes under the hood:
the code to check for the presence of matplotlib has been rewritten
new signal-slot connection syntax is used
completely rewritten code for calculating statistics
unused and duplicate code was removed and classes were moved into separate files
system font is used for histogram labels
The plugin now lives in my repository, please report bugs and feature requests by mail or in the bugtracker (preferred).
Victor Olaya has developed another framework for integrating various libraries and tools into QGIS. It is based on the SEXTANTE platform, which includes a toolbox, a graphical modeler and a script creator. It also provides a batch processing interface, command history, and some other features. The platform currently supports SAGA, GRASS, and R algorithms, as well as tools from the fTools and mmqgis plugins. According to the author, it is quite easy to add new algorithms and new providers.
I haven’t had a chance to test it properly yet, but it looks interesting and promising. The screenshot shows the list of tools, the GUI of the Basic Statistics tool from fTools and the result it produced.
SEXTANTE plugin in QGIS
Please note that this is still a work in progress, so regular users are better off waiting for the official release rather than using code from SVN.
In the post “Getting started with openModeller” I showed how to use openModeller Desktop to identify areas at risk from invasive species. Another task that can be done with openModeller is modelling the distribution of species under new climate conditions.
