By Erik Westra
Create your individual subtle functions to investigate and reveal geospatial details utilizing QGIS and Python
About This Book
- Make use of the geospatial functions of QGIS inside of your Python programs
- Build entire standalone mapping purposes according to QGIS and Python
- Use QGIS as a Python geospatial improvement environment
Who This publication Is For
If you're an skilled Python developer who desires to create your personal geospatial functions with minimal fuss, this is often the publication for you. whereas a few familiarity with mapping functions will be a bonus, no past wisdom of geospatial recommendations is needed. whether you could have by no means used QGIS earlier than, this publication will speedy get you as much as speed.
What you are going to Learn
- Use the Python Console to discover and regulate QGIS
- Perform geospatial improvement initiatives utilizing the PyQGIS Python library
- Create precious geospatial functions carried out as QGIS Python plugins
- Use QGIS as a standalone geoprocessing library inside your Python programs
- Build advanced interactive map-based GUIs inside your individual Python programs
- Understand how Python scripting can be utilized to customise the QGIS system
- Utilize the genuine power of Python and QGIS to create your personal whole mapping applications
QGIS is likely one of the most appropriate open resource Geographical details structures. whereas constructing Python geospatial functions should be tough, QGIS simplifies the method by way of combining the mandatory geoprocessing libraries with a worldly person interface, all of which are without delay managed utilizing Python code.
Starting with an advent to QGIS and the way to take advantage of the integrated QGIS Python Console, we are going to train you ways to put in writing Python code that uses the geospatial functions of QGIS. construction in this, you are going to eventually the right way to create your personal subtle standalone mapping purposes outfitted on best of QGIS. you are going to how to use the Python Console as a window into the QGIS programming setting, after which use that setting to create your personal Python scripts and plugins to customise QGIS. As your wisdom of the PyQGIS library grows, you are going to use it to accomplish numerous real-world geospatial programming projects, culminating within the construction of your personal advanced standalone purposes to load, learn, and show geospatial data.
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Extra info for Building Mapping Applications with QGIS
GeographicFlag()) We'll use this object to calculate the true length and area of the shapefile's features in meters and square meters respectively. getFeatures(QgsFeatureRequest()): ... For each feature, we want to calculate a label that identifies that feature. We'll do this by looking for an attribute called "name", "NAME", or "Name", and using that attribute's value as the feature label. If there is no attribute with one of these field names, we'll fall back to using the feature's ID instead.
It is also possible to create and manipulate geospatial data sources using the PyQGIS libraries. [ 38 ] Chapter 2 Scripting the QGIS user interface While the example program we created earlier has very limited user interaction, it is quite possible to build your program to directly use the QGIS user interface elements such as the status bar, the message bar, progress indicators, and the QGIS logging window. You can also create custom forms and windows so that the output of your program looks just like any other feature of QGIS itself.
Geometry() We can now use the QgsDistanceArea calculator we initialized earlier to calculate the length of a line feature and the area of a polygon feature. Line: ... Polygon: ... else: ... type()) feature_info = "geometry of type %s" % geom_type [ 37 ] The QGIS Python Console Now that we've done these calculations, we can display the feature's label together with the information we calculated about this feature: print "%s: %s" % (feature_label, feature_info) Finally, when we've finished iterating over the features, we can display the total line length and polygon area for all the features in the shapefile: print "Total length of all line features: %d" % tot_length print "Total area of all polygon features: %d" % tot_area This completes our program for analyzing the contents of a shapefile.