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.

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Table of Contents (18 chapters)
Title Page
Title Page
Copyright and Credits
Copyright and Credits
About Packt
About Packt
Contributors
Contributors
Preface
Preface
Free Chapter
1
A Refreshing Look at QGIS
A Refreshing Look at QGIS
Release schedules
QGIS downloading and installation
What's new?
A tour of QGIS
Working with CRS
Working with tables
Editing data
Composing maps
Adding functionality with plugins
Summary
2
Styling Raster and Vector Data
Styling Raster and Vector Data
Choosing and managing colors
Managing color ramps
Styling multiband rasters
Raster color rendering
Raster resampling
Styling vectors
Vector layer rendering
Using diagrams to display thematic data
Saving, loading, and setting default styles
Summary
3
Creating Spatial Databases
Creating Spatial Databases
Fundamental database concepts
Creating a spatial database
Connecting to a GeoPackage
Importing data into a GeoPackage
Working with tables
Exporting tables out of a GeoPackage
Creating queries and views
Summary
4
Preparing Vector Data for Processing
Preparing Vector Data for Processing
Merging vectors
Converting vector geometries
Adding geometry columns to an attribute table
Using basic vector Geoprocessing Tools
Defining coordinate reference systems
Advanced field calculations
Summary
5
Preparing Raster Data for Processing
Preparing Raster Data for Processing
Merging rasters
About converting raster files
Clipping a raster
Converting rasters into vectors
Converting from vector to raster (rasterize)
Reclassifying rasters 
Summary
6
Advanced Data Creation and Editing
Advanced Data Creation and Editing
What's new in editing?
Creating points from coordinate data
Geocoding address-based data
Georeferencing imagery
Checking the topology of vector data
Repairing topological errors via topological editing
Repairing an overlap between polygons
Example 3 – Repairing a gap between polygons
Summary
7
Advanced Data Visualization
Advanced Data Visualization
Using live layer effects
Creating beautiful effects with inverted polygon shapeburst fills
Using the 2.5D renderer
Creating 3D views 
Creating an Atlas
The power of geometry generators
Working with the Data Plotly plugin
Summary
8
The Processing Toolbox
The Processing Toolbox
Introducing the Processing Toolbox
What's new in the Processing Toolbox?
Configuring the Processing Toolbox
Viewing the Processing Toolbox
Using the Processing Toolbox
Performing raster analysis with GRASS
Performing analysis using SAGA
Exploring hydrologic analysis with SAGA
Summary
9
Automating Workflows with the Graphical Modeler
Automating Workflows with the Graphical Modeler
Introducing the graphical modeler
Working with your model
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
Interacting with the map canvas
Summary
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Index
Index

Converting rasters into vectors

Rasters can have limitations when it comes to querying them, and so it might be necessary to export a raster to a vector layer from time to time.

While this tool is very useful, we would urge you not to convert rasters that cover a large geographic area. It may be better to process individual tiles into vectors and then merge the vectors together at a later time.

Using the output from the previous section (if this is a temporary file, this will be called Clipped (Mask)), perform the following steps:

  1. Go to Raster | Conversion | Polygonize (Raster to vector).
  2. In the Polygonize (Raster to Vector) window, choose the Input Layer via the drop-down menu or Browser button. Choose Clipped (Mask).
  3. Choose the Band number (Band 1 (Gray)). You might want to experiment to see what the other bands produce.
  4. You can change the name of the field to be created, which will contain the Band value if you wish. The default is DN.
  5. Set the vectorized file location, name, and file type if...
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