May 2017
Beginner to intermediate
328 pages
7h 17m
English
Content preview from Mastering PostGIS
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Simplicity and validity
In PostGIS, there are two concepts: simplicity and validity. For most spatial analyses to succeed, input geometries have to be both simple and valid. Here are some rules:
- A point must always be simple and valid
- A MultiPoint must always be valid, and simple when there are no repeated points with identical coordinates
- A LineString or MultiLineString must always be valid, and is simple if the line:
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- Does not have repeated points (with the exception of closed rings, whose first and last point are identical)
- Does not self-intersect
Example of a non-simple line: self-intersecting autogenerated contours.
A polygon is ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.