Book Image

Mastering Geospatial Development with QGIS 3.x - Third Edition

By : Shammunul Islam, Simon Miles, Kurt Menke, GISP, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP
Book Image

Mastering Geospatial Development with QGIS 3.x - Third Edition

By: Shammunul Islam, Simon Miles, Kurt Menke, GISP, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP

Overview of this book

QGIS is an open source solution to GIS and widely used by GIS professionals all over the world. It is the leading alternative to proprietary GIS software. Although QGIS is described as intuitive, it is also, by default, complex. Knowing which tools to use and how to apply them is essential to producing valuable deliverables on time. Starting with a refresher on the QGIS basics and getting you acquainted with the latest QGIS 3.6 updates, this book will take you all the way through to teaching you how to create a spatial database and a GeoPackage. Next, you will learn how to style raster and vector data by choosing and managing different colors. The book will then focus on processing raster and vector data. You will be then taught advanced applications, such as creating and editing vector data. Along with that, you will also learn about the newly updated Processing Toolbox, which will help you develop the advanced data visualizations. The book will then explain to you the graphic modeler, how to create QGIS plugins with PyQGIS, and how to integrate Python analysis scripts with QGIS. By the end of the book, you will understand how to work with all aspects of QGIS and will be ready to use it for any type of GIS work.
Table of Contents (18 chapters)
Title Page
Copyright and Credits
About Packt
Contributors
Preface
Index

Nesting models


As we previously covered, when a model is saved to the models folder, it will appear in the Models category of the Processing Toolbox panel. What we didn't mention earlier was that it will also appear in the Algorithms tab of the Processing Modeler window. This means that a previously written model can be used as an algorithm in another model.

Note

Models won't appear as algorithms if some of their component algorithms are not available. This can happen if an algorithm provider is deactivated in Providers, and you can find this by navigating to Processing | Options. For example, if you have used a SAGA tool in a model but have subsequently deactivated SAGA tools, that model will not be available. As long as all the algorithms in a model are visible in the Processing Toolbox panel, a model will be available as an algorithm.

To demonstrate this feature, we will build on the model that we used in the previous section. The model clipped elevation data by watershed boundaries. With...