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-<!DOCTYPE html>
-<html>
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
- <meta name="apple-mobile-web-app-capable" content="yes">
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <title>Simplify a LineString geometry</title>
- <link rel="stylesheet" href="../theme/default/style.css" type="text/css">
- <link rel="stylesheet" href="style.css" type="text/css">
- <style type="text/css">
- #map, #map-simplify {
- height: 400px;
- width: 400px;
- margin: 5px !important;
- float: left;
- }
- #info {
- width: 300px;
- float: left;
- }
- #docs {
- clear: both;
- }
- </style>
- </head>
- <body>
- <h1 id="title">Simplify a LineString geometry</h1>
- <div id="tags">
- Douglas-Peucker, Douglas, Peucker, Peuker, tolerance
- </div>
- <p id="shortdesc">
- Shows the usage of the method &quot;simplify&quot; that implements
- the Douglas-Peucker algorithm to remove &quot;insignificant&quot;
- vertices from LineString geometries.
- </p>
- <div id="control-simplify">
- <label for="tolerance">Tolerance factor:</label>
- <input name="tolerance" id="tolerance" type="number" min="0" max="1" step="0.02" value="0.1">
- <input type="button" id="simplify" value="Simplify LineString">
- <input type="button" id="animation" value="Start animation">
- </div>
- <div id="map" class="smallmap">
- </div>
- <div id="map-simplify" class="smallmap">
- </div>
- <div id="info">
- </div>
- <div id="docs">
- <p>
- Instances of OpenLayers.Geometry.LineString have a method simplify,
- that can be used to simplify linestring geometries.
- Simplification sometimes is useful to enhance the perfomance of
- vector rendering or to reduce complexity of geometries. This
- might be especially handy when viewing geometries a small
- scales.
- </p>
- <p>
- OpenLayers.Geometry.LineString::simplify is a recursive
- implementation of the famous Douglas-Peucker algorithm. It is
- controlled by a tolerance factor that defines the threshold for
- vertices to be considered &quot;insignificant&quot; for the
- general structure of the geometry.
- </p>
- <p>
- The LineString on the left map can be simplified according to
- the tolerance value one enters in the form-field above the maps.
- Use a value between 0 and 1 for best results. If you navigate
- the left map, the right map will show the same location to make
- it easier to spot the differeces between the LineStrings.
- </p>
- <p>
- You can also use the button &quot;Start animation&quot; to get
- results for increasing tolerance-factors from 0.02 to 1.0. The
- animation can be paused by clicking on the button &quot;Stop
- animation&quot;.
- </p>
- <p>
- The LineString represents a part of the coastline of
- <a href="http://www.openstreetmap.org/?lat=54.7309684753418&amp;lon=83.1809234619141&amp;zoom=11">this
- place southeast of Novosibirsk in Russia</a> &mdash; found via
- <a href="http://ryba4.com/python/ramer-douglas-peucker">an
- example implementation of the algorithm in python</a>.
- </p>
- <p>
- For a detailled explanation of the algorithm see
- <a href="http://en.wikipedia.org/wiki/Douglas-Peucker_algorithm">the
- Wikipedia article</a> or the original publication: David Douglas
- &amp; Thomas Peucker, "Algorithms for the reduction of the
- number of points required to represent a digitized line or its
- caricature", The Canadian Cartographer 10(2), 112-122 (1973)
- (<a href="http://dx.doi.org/10.3138/FM57-6770-U75U-7727">DOI:
- 10.3138/FM57-6770-U75U-7727</a>).
- </p>
- <p>See <a href="simplify-linestring.js">simplify-linestring.js</a>
- for the source code of this example.</p>
- </div>
- <script type="text/javascript" src="../lib/OpenLayers.js">
- </script>
- <script type="text/javascript" src="./simplify-linestring.js">
- </script>
- </body>
-</html>