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Overview
Comment:Fixes to the geopoly documentation.
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA3-256:ab4f7977fbce340042ec39531f70d25cf2995bb10644163b1627244b02903eb5
User & Date: drh 2018-09-05 09:58:23
Context
2018-09-06
19:09
Updates the speed and size graph spreadsheet. check-in: e772c0fa3a user: drh tags: trunk
2018-09-05
09:58
Fixes to the geopoly documentation. check-in: ab4f7977fb user: drh tags: trunk
2018-09-03
10:57
Fix a typo in the CREATE TABLE documentation. check-in: aff4908d94 user: drh tags: trunk
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Changes to pages/geopoly.in.

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<h1>Overview</h1>

<p>
The Geopoly module is an alternative interface to the [R-Tree extension] that uses
the [http://geojson.org | GeoJSON] notation
([https://tools.ietf.org/html/rfc7946 | RFC-7946]) to describe two-dimensional
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 right-hand 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 counter-clockwise.

<p>







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<h1>Overview</h1>

<p>
The Geopoly module is an alternative interface to the [R-Tree extension] that uses
the [http://geojson.org | GeoJSON] notation
([https://tools.ietf.org/html/rfc7946 | RFC-7946]) to describe two-dimensional
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 right-hand 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 counter-clockwise.

<p>