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|Comment:||Fixes to the geopoly documentation.|
|Timelines:||family | ancestors | descendants | both | trunk|
|Files:||files | file ages | folders|
|User & Date:||drh 2018-09-05 09:58:23|
|19:09||Updates the speed and size graph spreadsheet. check-in: e772c0fa3a user: drh tags: trunk|
|09:58||Fixes to the geopoly documentation. check-in: ab4f7977fb user: drh tags: trunk|
|10:57||Fix a typo in the CREATE TABLE documentation. check-in: aff4908d94 user: drh tags: trunk|
Changes to pages/geopoly.in.
4 4 5 5 <h1>Overview</h1> 6 6 7 7 <p> 8 8 The Geopoly module is an alternative interface to the [R-Tree extension] that uses 9 9 the [http://geojson.org | GeoJSON] notation 10 10 ([https://tools.ietf.org/html/rfc7946 | RFC-7946]) to describe two-dimensional 11 -polygons. Geopoly includes functions for detecting when one polygons is 11 +polygons. Geopoly includes functions for detecting when one polygon is 12 12 contained within or overlaps with another, for computing the 13 -area contained within a polygon, for doing linear trasformations of polygons, 13 +area enclosed by a polygon, for doing linear trasformations of polygons, 14 14 for rendering polygons as 15 15 [https://en.wikipedia.org/wiki/Scalable_Vector_Graphics | SVG], and other 16 16 similar operations. 17 17 18 18 <p> 19 19 Geopoly operates on "simple" polygons - that is, polygons for which 20 20 the boundary does not intersect itself. Geopoly thus extends the capabilities ................................................................................ 37 37 a small subset of GeoJSON, but a critical subset. 38 38 In particular, GeoJSON understands 39 39 the JSON array of vertexes that describes a simple polygon. 40 40 41 41 <p>A polygon is defined by its vertexes. 42 42 Each vertex is a JSON array of two numeric values which are the 43 43 X and Y coordinates of the vertex. 44 -A polygon is a JSON array of these vertexes, and hence is an array 45 -of arrays. 44 +A polygon is a JSON array of at least four of these vertexes, 45 +and hence is an array of arrays. 46 46 The first and last vertex in the array must be the same. 47 47 The polygon follows the right-hand rule: When tracing a line from 48 48 one vertex to the next, the area to the right of the line is outside 49 49 of the polygon and the area to the left is inside the polygon. 50 50 In other words, the net rotation of the vertexes is counter-clockwise. 51 51 52 52 <p>