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  • Book Overview & Buying Mastering PostGIS
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Mastering PostGIS

Mastering PostGIS

By : George Silva, Mikiewicz, Michal Mackiewicz , Nycz
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Mastering PostGIS

Mastering PostGIS

1 (1)
By: George Silva, Mikiewicz, Michal Mackiewicz , Nycz

Overview of this book

PostGIS is open source extension onf PostgreSQL object-relational database system that allows GIS objects to be stored and allows querying for information and location services. The aim of this book is to help you master the functionalities offered by PostGIS- from data creation, analysis and output, to ETL and live edits. The book begins with an overview of the key concepts related to spatial database systems and how it applies to Spatial RMDS. You will learn to load different formats into your Postgres instance, investigate the spatial nature of your raster data, and finally export it using built-in functionalities or 3th party tools for backup or representational purposes. Through the course of this book, you will be presented with many examples on how to interact with the database using JavaScript and Node.js. Sample web-based applications interacting with backend PostGIS will also be presented throughout the book, so you can get comfortable with the modern ways of consuming and modifying your spatial data.
Table of Contents (10 chapters)
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Raster to vector conversion


The most useful function there for raster values to Vector is ST_DumpAsPolygons(). As a result we get geomval (set-of-records).

SELECT rid, (foo).* 
   FROM (SELECT rid, (ST_DumpAsPolygons(ST_Reclass((ST_SLOPE(rast::raster,'1'::int,'32BF'::text,'DEGREES'::text,'111120'::double precision))::raster, '1'::int,'0-5):1, 5-15]:2, [10-15:3, [15-25):4, 25-90]:5'::text,'32BF'::text))) FROM eudem.clip) AS foo; 

Another way to get some information is to query for values of raster cell at point of interest. As an example, let's check the value of DEM height for Istebna commune center:

mastering_postgis=# SELECT ST_Value(c.rast,(SELECT geom FROM raster_ops.places WHERE name='Istebna')) FROM eudem.clip c; 
     st_value      
------------------ 
 661.260009765625 
(1 row) 
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Mastering PostGIS
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