Sharing and visualizing rasters through SQL

In Chapter 4, Working with Vector Data – Advanced Recipes, we used gdal_translate to export PostGIS rasters to a file. This provides a method for transferring files from one user to another, or from one location to another. The only problem with this method is that you may not have access to the gdal_translate utility.

A different but equally functional approach is to use the ST_AsGDALRaster() family of functions available in PostGIS. In addition to ST_AsGDALRaster(), PostGIS provides ST_AsTIFF(), ST_AsPNG(), and ST_AsJPEG() to support the most common raster file formats.

To easily visualize raster files without the need for a GIS application, PostGIS 2.1 and later versions provide ST_ColorMap(). This function applies a built-in or user-specified color palette to a raster, that upon exporting with ST_AsGDALRaster(), can be viewed with any image viewer, such as a web browser.

Getting ready

In this recipe, we will use ST_AsTIFF() and ST_AsPNG()to export...