Graphics Reference
In-Depth Information
Summary
In this chapter, we took an in-depth look at the PyQGIS libraries and how you can use them
in your own programs. We learned that the QGIS Python libraries are implemented as
wrappers around the QGIS APIs implemented in C++. We saw how Python programmers
can understand and work with the QGIS reference documentation, even though it is written
for C++ developers. We also looked at the way the PyQGIS libraries are organized into dif-
ferent packages, and learned about the most important classes defined in the qgis.core
and qgis.gui packages.
We then saw how a coordinate reference systems (CRS) is used to translate from points on
the three-dimensional surface of the Earth to coordinates within a two-dimensional map
plane.
We learned that vector format data is made up of features, where each feature has an ID, a
geometry, and a set of attributes, and that symbols are used to draw vector geometries onto
a map layer, while renderers are used to choose which symbol to use for a given feature.
We learned how a spatial index can be used to speed up access to vector features.
Next, we saw how raster format data is organized into bands that represent information
such as color, elevation, and so on, and looked at the various ways in which a raster data
source can be displayed within a map layer. Along the way, we learned how to access the
contents of a raster data source.
Finally, we looked at various techniques for performing useful tasks using the PyQGIS lib-
rary.
In the next chapter, we will learn more about QGIS Python plugins, and then go on to use
the plugin architecture as a way of implementing a useful feature within a mapping applica-
tion.
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