Mastering QGIS电子书

Mastering QGIS

Table of Contents

Mastering QGIS

Credits

Foreword

About the Authors

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers, and more

Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Downloading the color images of this book

Errata

Piracy

Questions

1. A Refreshing Look at QGIS

QGIS download and installation

Installing QGIS on Windows

Installing QGIS on Mac OS X

Installing QGIS on Ubuntu Linux

Installing QGIS only

Installing QGIS and other FOSSGIS Packages

Tour of QGIS

QGIS Desktop

QGIS Browser

Loading data

Loading vector data

Loading raster data

Loading databases

Web services

Working with coordinate reference systems

Working with tables

Table joins

Editing data

Snapping

Styling vector data

Styling raster data

Contrast enhancement

Blending modes

Composing maps

Adding functionality with plugins

Summary

2. Creating Spatial Databases

Fundamental database concepts

Database tables

Table relationships

Structured Query Language

Creating a spatial database

Importing data into a SpatiaLite database

Importing KML into SpatiaLite

Importing a shapefile into SpatiaLite

Importing tables into SpatiaLite

Exporting tables out of SpatiaLite as a shapefile

Managing tables

Creating a new table

Renaming a table

Editing table properties

Deleting a table

Emptying a table

Creating queries and views

Creating a SQL query

Creating a spatial view

Dropping a spatial view

Summary

3. Styling Raster and Vector Data

Choosing and managing colors

Always available color picker components

Changeable panels in the color picker

Color ramp

Color wheel

Color swatches

Color sampler

Managing color ramps

Managing the QGIS color ramp collection

Renaming a color ramp

Removing a color ramp

Exporting a color ramp

Importing a color ramp

Adding a color ramp

Adding a Gradient color ramp

Adding a Random color ramp

Add a ColorBrewer color ramp

Adding a cpt-city color ramp

Editing a color ramp

Styling single band rasters

Paletted raster band rendering

Singleband gray raster band rendering

Singleband pseudocolor raster band rendering

Styling multiband rasters

Creating a raster composite

Raster color rendering

Raster resampling

Styling vectors

Single-symbol vector styling

Categorized vector styling

Graduated vector styling

Rule-based vector styling

Point-displacement vector styling

Inverted polygons vector styling

Vector layer rendering

Using diagrams to display thematic data

Parameters common to all diagram types

Diagram size parameters

Diagram position parameters

Adding attributes to diagrams

Creating a pie chart diagram

Creating a text chart diagram

Creating a histogram chart diagram

Saving, loading, and setting default styles

Saving a style

Loading a style

Setting and restoring a default style

Summary

4. Preparing Vector Data for Processing

Merging shapefiles

Creating spatial indices

Checking for geometry errors

Converting vector geometries

Creating polygon centroids

Converting polygons to lines and lines to polygons

Creating polygons surrounding individual points

Extracting nodes from lines and polygons

Simplifying and densifying features

Converting between multipart and singlepart features

Adding geometry columns to an attribute table

Using basic vector geoprocessing tools

Spatial overlay tools

Using the Clip and Difference tools

Using the Intersect and Symmetrical Difference tools

Overlaying polygon layers with Union

Creating buffers

Generating convex hulls

Dissolving features

Defining coordinate reference systems

Understanding the Proj.4 definition format

Defining a new custom coordinate reference system

Advanced field calculations

Exploring the field calculator interface

Writing advanced field calculations

The first example – calculating and formatting the current date

The second example – inserting geometric values

The third example – calculating a population-dependent label string

Complex spatial and aspatial queries

Summary

5. Preparing Raster Data for Processing

Reclassifying rasters

Converting datasets from floating-point to integer rasters

Resampling rasters

Installing and troubleshooting SAGA on different platforms

Windows

Mac OS X

Linux

Rescaling rasters

Creating a raster mosaic

Generating raster overviews (pyramids)

Converting between raster and vector data models

Converting from raster to vector

Converting from vector to raster (rasterize)

Creating raster surfaces via interpolation

Summary

6. Advanced Data Creation and Editing

Creating points from coordinate data

Mapping well-known text representations of geometry

Geocoding address-based data

How address geocoding works

The first example – geocoding using web services

The second example – geocoding using local street network data

Georeferencing imagery

Ground control points

Using the Georeferencer GDAL plugin

The first example – georeferencing using a second dataset

Getting started

Entering the ground control points

Transformation settings

Completing the operation

The second example – georeferencing using a point file

Checking the topology of vector data

Installing the Topology Checker

Topological rules

Rules for point features

Rules for line features

Rules for polygon features

Using the Topology Checker

Repairing topological errors via topological editing

Example 1 – resolving duplicate geometries

Example 2 – repairing overlaps

Setting the editing parameters

Repairing an overlap between polygons

Example 3 – repairing a gap between polygons

Summary

7. The Processing Toolbox

About the processing toolbox

Configuring the processing toolbox

Understanding the processing toolbox

Using the processing toolbox

Performing raster analyses with GRASS

Calculating shaded relief

Calculating the least-cost path

Calculating the slope using r.slope

Reclassifying a new slope raster and the land use raster

Combining reclassified slope and land use layers

Calculating the cumulative cost raster using r.cost

Calculating the cost path using least-cost paths

Evaluating a viewshed

Clipping elevation to the boundary of a park using GDAL

Calculating viewsheds for towers using r.viewshed

Combining viewsheds using r.mapcalculator

Calculating raster statistics using r.stats

SAGA

Evaluating a habitat

Calculating elevation ranges using the SAGA Raster calculator

Clipping land use to the park boundary using Clip grid with polygon

Querying land use for only surface water using the SAGA Raster calculator

Finding proximity to surface water using GDAL Proximity

Querying the proximity for 1,000 meters of water using the GDAL Raster calculator

Reclassifying land use using the Reclassify grid values tool

Combining raster layers using the SAGA Raster calculator

Exploring hydrologic analyses with TauDEM

Removing pits from the DEM

Calculating flow directions across the landscape

Calculating the upstream area above Fort Klamath

Calculating a stream network raster grid

Creating a watershed-specific vector stream network

R

Exploring summary statistics and histograms

Summary

8. Automating Workflows with the Graphical Modeler

An introduction to the graphical modeler

Opening the graphical modeler

Configuring the modeler and naming a model

Adding inputs

Adding algorithms

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

9. Creating QGIS Plugins with PyQGIS and Problem Solving

Webography - where to get API information and PyQGIS help

PyQGIS cookbook

API documentation

The QGIS community, mailing lists, and IRC channel

Mailing lists

IRC channel

The StackExchange community

Sharing your knowledge and reporting issues

The Python Console

Getting sample data

My first PyQGIS code snippet

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

Installing Plugin Builder

Locating plugins

Creating my first Python plugin – TestPlugin

Setting mandatory plugin parameters

Setting optional plugin parameters

Generating the plugin code

Compiling the icon resource

The plugin file structure – where and what to customize

Exploring main plugin files

Plugin Builder generated files

A simple plugin example

Adding basic logic to TestPlugin

Modifying the layout with Qt Designer

Adding two pull-down menus

Modifying the GUI logic

Modifying the plugin logic

Classifying layers

Populating the combobox

Understanding self

Showing and running the dialog

Some improvements

More detail of the code

Setting up a debugging environment

What is a debugger?

Installing Aptana

Setting up PYTHONPATH

Starting the Pydevd server

Connecting QGIS to the Pydevd server

Debugging session example

Creating a PyDev project for TestPlugin

Adding breakpoints

Debugging in action

Summary

10. PyQGIS Scripting

Where to learn Python basics

Tabs or spaces, make your choice!

Loading layers

Managing rasters

Exploring QgsRasterLayer

Visualizing the layer

Managing vector files

Managing database vectors

Vector structure

The basic vector methods

Describing the vector structure

Describing the header

Describing the rows

Exploring QgsGeometry

Iterating over features

Describing the iterators

Editing features

Updating canvas and symbology

Editing through QgsVectorDataProvider

Changing a feature's geometry

Changing a feature's attributes

Deleting a feature

Adding a feature

Editing using QgsVectorLayer

Discovering the QgsVectorLayerEditBuffer class

Changing a feature's geometry

Changing a feature's attributes

Adding and removing a feature

Running processing toolbox algorithms

Looking for an algorithm

Getting algorithm information

Running algorithms from the console

Running your own processing script

Creating a test processing toolbox script

Looking at the custom script

Running the script

Running an external algorithm or command

Running a simple command

Interacting with the map canvas

Getting the map canvas

Explaining Map Tools

Setting the current Map Tool

Getting point-click values

Getting the current Map Tool

Creating a new Map Tool

Creating a map canvas event handler

Creating a Map Tool event handler

Setting up the new Map Tool

Using point-click values

Exploring the QgsRubberBand class

Summary

Index