segunda-feira, 17 de janeiro de 2011

Travelling through Brazil with Quantum GIS

Your favorite GIS software now also helps you in your vacations! On this post I show how to trace routes on brazilian highways using QGIS and also navigate using GoogleMaps' satelite images.

First, the requirements:
Data: Seamless 1:1.000.000 Digital Chart of Brazil (available at IBGE)
Softwares: Quantum GIS 1.6+ RoadGraph Plugin (available for win32 e linux) + OpenLayers Plugin (available though the python plugins repository)

Ps.: RoadGraph Plugin is going to be included on QGIS oficial 1.7 release

First, let's load our data. The layer called ST_Rodovias stores every brazilian highway*. When the RoadGraph plugin is installed (by copying the dll to c:\osgeo4w\apps\qgis\plugins\ on OSGeo4W's builds), there is a small box on the bottom left side of the screen for routes tracing. We choose origin, destination and the plugin traces the route as shown in the image bellow.

* On scale 1.100.000 almost every bridge and tunnel are represented as dots. If we wish to be more accurate we should merge the ST_Rodovias layer with ST_Ponte_Tunel where the line represented tunnels and bridges are stored.

With the mouse right button over the layer "shortest path" we can export our route to ShapeFile. This way the software is able to reproject it later over the imagery.

Now we can load OpenLayers plugin:

And the result, as expected is the visualization of our route over Google Maps' imagery.

The great deal about this solution is that it allows GIS analisys over the route traced. It's a desired feature for some brazilian highway departments when they need to know the distance between cities in the country. It's also possible to know which citties are near a travel route and how they are going to be affected if this changes. These analisys are possible because we are working with a full-featured GIS software with a suficiently complete Dataset.

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