Book Image

Mastering QGIS - Second Edition

By : Kurt Menke, GISP, Paolo Corti, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP
Book Image

Mastering QGIS - Second Edition

By: Kurt Menke, GISP, Paolo Corti, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP

Overview of this book

QGIS is an open source solution to GIS. It is widely used by GIS professionals all over the world. It is the leading alternative to the 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, this book will take you all the way through to creating your first custom QGIS plugin. From the refresher, we will recap how to create, populate, and manage a spatial database. You’ll also walk through styling GIS data, from creating custom symbols and color ramps to using blending modes. In the next section, you will discover how to prepare vector, heat maps, and create live layer effects, labeling, and raster data for processing. You’ll also discover advanced data creation and editing techniques. The last third of the book covers the more technical aspects of QGIS such as using LAStools and GRASS GIS’s integration with the Processing Toolbox, how to automate workflows with batch processing, and how to create graphical models. Finally, you will see how to create and run Python data processing scripts and write your own QGIS plugin with pyqgis. By the end of the book, you will understand how to work with all the aspects of QGIS, and will be ready to use it for any type of GIS work.

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Mastering QGIS - Second Edition
Kurt Menke, GISP | Paolo Corti | Richard Smith Jr., GISP | Luigi Pirelli | John Van Hoesen, GISP
Sep, 2016 | 486 pages
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Table of Contents (19 chapters)
Mastering QGIS - Second Edition
Mastering QGIS - Second Edition
Credits
Credits
Foreword
Foreword
About the Authors
About the Authors
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
A Refreshing Look at QGIS
A Refreshing Look at QGIS
Release schedules
QGIS download and installation
Tour of QGIS
Loading data into QGIS Desktop
Working with CRS
Working with tables
Editing data
Composing maps
Adding functionality with plugins
Summary
2
Creating Spatial Databases
Creating Spatial Databases
Fundamental database concepts
Creating a spatial database
Importing data into a SpatiaLite database
Exporting tables out of SpatiaLite
Managing tables
Creating queries and views
Summary
3
Styling Raster and Vector Data
Styling Raster and Vector Data
Choosing and managing colors
Managing color ramps
Styling singleband rasters
Styling multiband rasters
Creating a raster composite
Raster color rendering
Raster resampling
Styling vectors
Vector layer rendering
Using diagrams to display thematic data
Saving, loading, and setting default styles
Summary
4
Preparing Vector Data for Processing
Preparing Vector Data for Processing
Merging shapefiles
Creating spatial indices
Checking for geometry errors
Converting vector geometries
Using basic vector geoprocessing tools
Defining coordinate reference systems
Viewing a statistical summary of vector layers
Advanced field calculations
Conditional formatting for attribute table cells
Complex spatial and aspatial queries
Summary
5
Preparing Raster Data for Processing
Preparing Raster Data for Processing
Reclassifying rasters for analysis
Rescaling raster values
Aligning raster pixels
Creating a raster mosaic
Generating raster overviews (pyramids)
Converting between raster and vector data models
Creating raster surfaces via interpolation
Summary
6
Advanced Data Creation and Editing
Advanced Data Creation and Editing
Creating points from coordinate data
Geocoding address-based data
Georeferencing imagery
Checking the topology of vector data
Repairing topological errors via topological editing
Summary
7
Advanced Data Visualization
Advanced Data Visualization
Learn to use live layer effects
Creating beautiful effects with inverted polygon shapeburst fills
Creating 3D views with QGIS2ThreeJS
Creating an Atlas
Summary
8
The Processing Toolbox
The Processing Toolbox
About the Processing Toolbox
Performing raster analyses with GRASS
SAGA
Exploring hydrologic analyses with TauDEM
R
LAStools and Fusion
Summary
9
Automating Workflows with the Graphical Modeler
Automating Workflows with the Graphical Modeler
An introduction to the graphical modeler
Opening the graphical modeler
Configuring the modeler and naming a model
Adding data inputs to your model
Adding algorithms to your model
Running a model
Editing a model
Documenting a model
Saving, loading, and exporting models
Executing model algorithms iteratively
Nesting models
Using batch processing with models
Converting a model into a Python script
Summary
10
Creating QGIS Plugins with PyQGIS and Problem Solving
Creating QGIS Plugins with PyQGIS and Problem Solving
Webography – where to get API information and PyQGIS help
The Python Console
My second PyQGIS code snippet – looping the layer features
Exploring iface and QGis
Exploring a QGIS API in the Python Console
Creating a plugin structure with Plugin Builder
A simple plugin example
Setting up a debugging environment
Debugging session example
Summary
11
PyQGIS Scripting
PyQGIS Scripting
Where to learn Python basics
How to load layers
Vector structure
Iterating over features
Editing features
Running Processing Toolbox algorithms
Running an external algorithm or command
Interacting with the map canvas
Summary
Index
Index

Vector structure

To describe the QgsVectorLayer class, we will first approach basic layer parameters, and then we will explore how the vector is organized. We will explore some classes that are involved in the vector structure, which represent rows and headers.

The basic vector methods

We will explore the vector class working on a real vector; we will load alaska.shp in the myVector variable.

This variable is an instance of the QgsVectorLayer class. This means that all methods of the vector are documented at http://qgis.org/api/classQgsVectorLayer.html. As for rasters, this class is a specialization of the generic QgsMapLayer class.

To get the extent of the layer, it's necessary to use the extent() method of the QgsMapLayer class:

print myVector.extent().toString()

Executing the preceding code will generate the following result:

-7115212.9837922714650631,1368239.6063178631011397 : 4895579.8114661639556289,7805331.2230994049459696

This shows the corner coordinates in the format xmin,ymin: xmax...

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