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Overview
Comment:Fixes to the geopoly documentation.
Timelines: family | ancestors | descendants | both | trunk
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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.

     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>