Geoprocessing with Python

362 Pages·2016·28.17 MB·English

by  Chris Garrard

Chris Garrard
M A N N I N G
Geoprocessing with Python
ii
Geoprocessing
with Python
CHRIS GARRARD
MANNING
SHELTER ISLAND
iv
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Printed in the United States of America
1 2 3 4 5 6 7 8 9 10 – EBM – 21 20 19 18 17 16
brief contents
1 ■ Introduction 1
2 ■ Python basics 15
3 ■ Reading and writing vector data 35
4 ■ Working with different vector file formats 67
5 ■ Filtering data with OGR 88
6 ■ Manipulating geometries with OGR 105
7 ■ Vector analysis with OGR 129
8 ■ Using spatial reference systems 153
9 ■ Reading and writing raster data 173
10 ■ Working with raster data 208
11 ■ Map algebra with NumPy and SciPy 237
12 ■ Map classification 276
13 ■ Visualizing data 287
v
vi BRIEF CONTENTS
contents
preface xi
acknowledgments xiii
about this book xiv
about the author xvii
about the cover illustration xviii
1 Introduction 1
1.1 Why use Python and open source? 2
1.2 Types of spatial data 3
1.3 What is geoprocessing? 7
1.4 Exploring your data 10
1.5 Summary 14
2 Python basics 15
2.1 Writing and executing code 16
2.2 Basic structure of a script 17
2.3 Variables 18
2.4 Data types 20
Booleans 20 ■ Numeric types 20 ■ Strings 22
Lists and tuples 24 ■ Sets 26 ■ Dictionaries 26
2.5 Control flow 27
If statements 27 ■ While statements 29 ■ For
statements 29 ■ break, continue, and else 30
2.6 Functions 31
2.7 Classes 32
2.8 Summary 34
vii
viii CONTENTS
3 Reading and writing vector data 35
3.1 Introduction to vector data 36
3.2 Introduction to OGR 41
3.3 Reading vector data 44
Accessing specific features 47 ■ Viewing your data 49
3.4 Getting metadata about the data 51
3.5 Writing vector data 54
Creating new data sources 59 ■ Creating new fields 61
3.6 Updating existing data 63
Changing the layer definition 63 ■ Adding, updating, and
deleting features 64
3.7 Summary 66
4 Working with different vector file formats 67
4.1 Vector file formats 68
File-based formats such as shapefiles and geoJSON 68
Multi-user database formats such as PostGIS 71
4.2 Working with more data formats 71
SpatiaLite 72 ■ PostGIS 73 ■ Folders as data sources
(shapefiles and CSV) 74 ■ Esri file geodatabases 74
Web feature services 76
4.3 Testing format capabilities 84
4.4 Summary 87
5 Filtering data with OGR 88
5.1 Attribute filters 89
5.2 Spatial filters 93
5.3 Using SQL to create temporary layers 99
5.4 Taking advantage of filters 103
5.5 Summary 104
6 Manipulating geometries with OGR 105
6.1 Introduction to geometries 106
6.2 Working with points 107
Creating and editing single points 108 ■ Creating and editing
multipoints: multiple points as one geometry 110
6.3 Working with lines 112
Creating and editing single lines 114 ■ Creating and editing
multilines: multiple lines as one geometry 118
CONTENTS ix
6.4 Working with polygons 120
Creating and editing single polygons 122 ■ Creating and
editing multipolygons: multiple polygons as one geometry 124
Creating and editing polygons with holes: donuts 126
6.5 Summary 128
7 Vector analysis with OGR 129
7.1 Overlay tools: what’s on top of what? 130
7.2 Proximity tools: how far apart are things? 136
7.3 Example: locating areas suitable for wind farms 140
7.4 Example: animal tracking data 144
7.5 Summary 152
8 Using spatial reference systems 153
8.1 Introduction to spatial reference systems 154
8.2 Using spatial references with OSR 159
Spatial reference objects 159 ■ Creating spatial reference
objects 161 ■ Assigning an SRS to data 163 ■ Reprojecting
geometries 164 ■ Reprojecting an entire layer 167
8.3 Using spatial references with pyproj 168
Transforming coordinates between spatial reference systems 169
Great-circle calculations 171
8.4 Summary 172
9 Reading and writing raster data 173
9.1 Introduction to raster data 174
9.2 Introduction to GDAL 181
9.3 Reading partial datasets 187
Using real-world coordinates 193 ■ Resampling data 196
9.4 Byte sequences 200
9.5 Subdatasets 203
9.6 Web map services 204
9.7 Summary 207
10 Working with raster data 208
10.1 Ground control points 209
10.2 Converting pixel coordinates to another image 213
10.3 Color tables 215
Transparency 217