QGIS (I)

Like I mentioned before, QGIS (Quantum GIS) is a free GIS. It’s a Qt/C++ application (Anno.: it is NOT a Java-application, as I mentioned before! Changed April 4th 2007) and with that it is not depending on your pc’s operating system (as long as you can get a Qt environment for it!). I cannot promise that this is true for all the plug-ins. I use it on Linux and on MS Windows . You can fetch the binaries or th e source of QGIS from the QGIS-homepage (sourcecode is not recommende). There you can also find an english documentation and the usal forums where you can find additional help.

The installatio of QGIS on a Windows-machine ends without errors and after a few minutes you can start with some sampledata. Ideally you have some shape-files of your own objects already. If not, you can fetch sampladata out of the internet. Googling helps! After that I would advice you to “play around” with your sampledata to become familiar with the gui and the functions. The gui of QGIS version 0.7.4 ‘Seamus’ is available in many languages –even in german and shouldn’t make you any great problems. A german translation of the documentation (Install-/Userguide) will be available for version 0.8. For a detailed view on all the functions you should have a look at the userguide. Maybe I have a limited view on th e software, because I personally don’t need all the functions included. And by the way: this is not a product test.

I start -like I always do- by saving an empty project. Then I open some shape-files with roads, buildings and rivers. They are displayed by QGIS with a random color. I could change the color and save this with the projectfile. If more than one should work with the data you can place the projectfile somewhere in the network where it is avaiable for all and then you can make it readonly. Everyone can now open this project but cannot save any changes. If people should also change data you have to talk about alternative ways. At the moment only the administrator has the possibility to insert, change or delete layers from the project.

After a short time I cannot resist to test the connection to PostGIS. But I still have no data in PostGIS! Where can I get them? Nothing easier than this! šŸ™‚
QGIS has an build-in importtool for shape-files. Someone has thought about it! After a short time I have added my three shapefiles to the importfilter and with the same high speed my files where imported into PostGIS. And now? Now I can access them in PostGIS instead of the shapefile.

The advance lays on the hand: I use the data to view them in QGIS and maybe change the geometry if neccessary. Maybe there are other tables in their, which are related to my data by some kind of ID. Because of that I can connect this tables with my data and can give them a reference in my maps.

An example:
I have a table with spatial information about buildings. This table is normalised – better say: as simple as can be. It contains no more information then the geometry and the unique IDs of the buildings. These IDs originally came from a table with a lot more information. Without having tested it before, you can now create a view (a kind of dynamic table based on a SQL-statement) which connects the geometrydata and the additional alphanumeric data with the ID of the buildings in both tables. If you now use the view to show you data in QGIS, you cannot only see the buldings but access the additional data, too.
The other way round, I would like to get the information about other objects and poi (points of interest) in a maximum of 500metres around my object. All these data can be found in my database so I can use them for a spatial analysis and put them together in a report. I’m sure that you can extend the report to get the detailed distanc of each poi. In an external application it will be easy to add another column with the time you would need for this distance walking. šŸ™‚

Possibillities without end — if you just catch the importance of these information! Later I will give you more specifications working with QGIS, PostGIS and PostgreSQL … I promise! šŸ™‚

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