Dr JTS
There is an elegant mathematical theory of binary relations. Homogeneous relations are an important subclass of binary relations in which both domains are the same. A homogeneous relation R is a subset of all ordered pairs (x,y) with x and y elements of the domain. This can be thought of as a...
Dr JTS
The previous post introduced the new ConcaveHullOfPolygons class in the JTS Topology Suite. This allows computing a concave hull which is constrained by a set of polygonal geometries. This supports use cases including:generalization of groups of polygonjoining polygonsfilling gaps between...
Dr JTS
A common spatial need is to find a polygon that accurately represents a set of points. The convex hull of the points often does not provide this, since it can enclose large areas which contain no points. What is required is a non-convex hull, often termed the concave hull. The Convex Hull and a...
Abel Vázquez
0. What’s this and what’s not This is not an SQL course, not even a crash-course, not a introduction, not a master class… It’s just a compilation of tips, tricks or unusual uses of PostgreSQL / PostGIS that I use a lot and may be helpful for anybody out there. Just try to keep your brain within...
Abel Vázquez
First of all, what is an isovist? It’s simply the same as a viewshed… and what the heck is a viewshed? Let’s go to the Wikipedia: A single isovist is the volume of space visible from a given point in space, together with a specification of the location of that point The decision of using the...