Creating a layer-definition file

Layer styling is one of the most complex aspects of the QGIS Python API. Once you've developed the style for a layer, it is often useful to save the styling to the QGIS Markup Language (QML) XML format.

Getting ready

You will need to download the following zipped directory, named saveqml, and decompress it to your qgis_data/rasters directory:

https://github.com/GeospatialPython/Learn/raw/master/saveqml.zip

How to do it...

We will create a color ramp for a digital elevation model (DEM) and then make it semi-transparent for overlay on a hillshaded tiff of the DEM. We'll save the style we create to a QML file:

1. First, we'll need the Python Qt libraries:

           from PyQt4.QtCore import * 
           from PyQt4.QtGui import * 
   

2. Next, we'll load up our two raster layers:

           hs = QgsRasterLayer("/qgis_data/saveqml/hillshade.tif",
                               "Hillshade") 
           dem = QgsRasterLayer("/qgis_data/saveqml/dem.asc", "DEM") 
   

3. Then...