Chapter 6. Raster Data Processing

Geographic information systems (GIS) are often comprised of points, lines, and polygons. These data types are called vector data. There is, however, another data type in GIS—rasters. In this chapter, you will learn the basics of working with raster data. You will learn how to:

• Use the Geospatial Data Abstraction Library (GDAL) to load and query rasters
• Use GDAL to modify and save rasters
• Use GDAL to create rasters
• Load rasters into PostgreSQL
• Perform queries on rasters using PostgreSQL

Note

Installing GDAL can be difficult. By using virtual environments and running Anaconda, you can simplify this process by using the GUI of the environment.

Raster operations using GDAL

The GDAL library allows you to read and write both vector and raster data. To install GDAL on Windows, you will need the appropriate binaries:

Note

You can download OSGeo4W, which contains the binaries, at: https://trac.osgeo.org/osgeo4w/

When you have the binaries, you can install gdal using conda, as follows:

conda install -c conda-forge gdal

In the following sections, you will learn how to load and work with a .tif file.

Using the GDAL library to load and query rasters

Now that you have gdal installed, import it using:

from osgeo import gdal

GDAL 2 is the most recent version. If you have an older version of gdal installed, you may need to import it using the following code:

import gdal

If this is the case, you may want to look into upgrading your version of gdal. Once you have gdal imported, you can open a raster image. First, let's get an image from the web. The Earth Data Analysis Center at the University of New Mexico maintains the Resource Geographic Information...

Raster operations using PostgreSQL

In the first section of this chapter, you were able to load, display, and query rasters using gdal. In this section, you will learn how to load and query rasters using a spatial database—PostgreSQL. As you start to model your data, you will most likely hold it in a spatial database. You can leverage your database to perform the queries on your rasters.

Loading rasters into PostgreSQL

To load a raster into PostgreSQL, you can use the raster2pgsql binary. If it is not in your path, you may need to add it. You should be able to find the binary in your PostgreSQL install directory on Windows at \PostgreSQL\10\bin.

The following command should be executed from your operating system's command line. It will load the TIF you created earlier in this chapter into an existing PostgreSQL database:

>raster2pgsql -I -C -s 4326 C:\Users\Paul\Desktop\BigI.tif public.bigi | psql -U postgres -d pythonspatial

The previous command uses raster2pgsql with the -I (creates an index...

Summary

In this chapter, you learned how to use GDAL and PostgreSQL to work with raster data.

First, you learned how to use the GDAL to load and query rasters. You also learned how to use GDAL to modify and save rasters. Then, you learned how to create your own raster data. You learned how to load raster data into PostgreSQL using the raster2pgsql tool. Once in PostgreSQL, you learned how to query for metadata, attributes, values, and geometry. You learned several common functions within PostgreSQL for raster data analysis. 

While this chapter only scratched the surface of working with raster data, you should have enough knowledge now to know how to learn new techniques and methods for working with rasters. In the next chapter, you will learn how to work with vector data in PostgreSQL.