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Overview
Comment:  Fixes to the geopoly documentation. 

Timelines:  family  ancestors  descendants  both  trunk 
Files:  files  file ages  folders 
SHA3256:  ab4f7977fbce340042ec39531f70d25cf2995bb10644163b1627244b02903eb5 
User & Date:  drh 20180905 09:58:23 
Context
20180906
 
19:09  Updates the speed and size graph spreadsheet. checkin: e772c0fa3a user: drh tags: trunk  
20180905
 
09:58  Fixes to the geopoly documentation. checkin: ab4f7977fb user: drh tags: trunk  
20180903
 
10:57  Fix a typo in the CREATE TABLE documentation. checkin: aff4908d94 user: drh tags: trunk  
Changes
Changes to pages/geopoly.in.
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<h1>Overview</h1> <p> The Geopoly module is an alternative interface to the [RTree extension] that uses the [http://geojson.org  GeoJSON] notation ([https://tools.ietf.org/html/rfc7946  RFC7946]) to describe twodimensional polygons. Geopoly includes functions for detecting when one polygons is contained within or overlaps with another, for computing the area contained within a polygon, for doing linear trasformations of polygons, for rendering polygons as [https://en.wikipedia.org/wiki/Scalable_Vector_Graphics  SVG], and other similar operations. <p> Geopoly operates on "simple" polygons  that is, polygons for which the boundary does not intersect itself. Geopoly thus extends the capabilities ................................................................................ a small subset of GeoJSON, but a critical subset. In particular, GeoJSON understands the JSON array of vertexes that describes a simple polygon. <p>A polygon is defined by its vertexes. Each vertex is a JSON array of two numeric values which are the X and Y coordinates of the vertex. A polygon is a JSON array of these vertexes, and hence is an array of arrays. The first and last vertex in the array must be the same. The polygon follows the righthand rule: When tracing a line from one vertex to the next, the area to the right of the line is outside of the polygon and the area to the left is inside the polygon. In other words, the net rotation of the vertexes is counterclockwise. <p> 





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<h1>Overview</h1> <p> The Geopoly module is an alternative interface to the [RTree extension] that uses the [http://geojson.org  GeoJSON] notation ([https://tools.ietf.org/html/rfc7946  RFC7946]) to describe twodimensional polygons. Geopoly includes functions for detecting when one polygon is contained within or overlaps with another, for computing the area enclosed by a polygon, for doing linear trasformations of polygons, for rendering polygons as [https://en.wikipedia.org/wiki/Scalable_Vector_Graphics  SVG], and other similar operations. <p> Geopoly operates on "simple" polygons  that is, polygons for which the boundary does not intersect itself. Geopoly thus extends the capabilities ................................................................................ a small subset of GeoJSON, but a critical subset. In particular, GeoJSON understands the JSON array of vertexes that describes a simple polygon. <p>A polygon is defined by its vertexes. Each vertex is a JSON array of two numeric values which are the X and Y coordinates of the vertex. A polygon is a JSON array of at least four of these vertexes, and hence is an array of arrays. The first and last vertex in the array must be the same. The polygon follows the righthand rule: When tracing a line from one vertex to the next, the area to the right of the line is outside of the polygon and the area to the left is inside the polygon. In other words, the net rotation of the vertexes is counterclockwise. <p> 