e8960054a9
git-svn-id: http://svn.openlayers.org/trunk/openlayers@12082 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf
104 lines
4.7 KiB
HTML
104 lines
4.7 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
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<meta name="apple-mobile-web-app-capable" content="yes">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Simplify a LineString geometry</title>
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<link rel="stylesheet" href="../theme/default/style.css" type="text/css">
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<link rel="stylesheet" href="style.css" type="text/css">
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<style type="text/css">
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#map, #map-simplify {
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height: 400px;
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width: 400px;
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margin: 5px !important;
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float: left;
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}
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#info {
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width: 300px;
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float: left;
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}
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#docs {
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clear: both;
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}
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</style>
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</head>
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<body>
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<h1 id="title">Simplify a LineString geometry</h1>
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<div id="tags">
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Douglas-Peucker, Douglas, Peucker, Peuker, tolerance
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</div>
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<p id="shortdesc">
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Shows the usage of the method "simplify" that implements
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the Douglas-Peucker algorithm to remove "insignificant"
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vertices from LineString geometries.
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</p>
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<div id="control-simplify">
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<label for="tolerance">Tolerance factor:</label>
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<input name="tolerance" id="tolerance" type="number" min="0" max="1" step="0.02" value="0.1">
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<input type="button" id="simplify" value="Simplify LineString">
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<input type="button" id="animation" value="Start animation">
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</div>
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<div id="map" class="smallmap">
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</div>
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<div id="map-simplify" class="smallmap">
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</div>
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<div id="info">
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</div>
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<div id="docs">
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<p>
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Instances of OpenLayers.Geometry.LineString have a method simplify,
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that can be used to simplify linestring geometries.
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Simplification sometimes is useful to enhance the perfomance of
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vector rendering or to reduce complexity of geometries. This
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might be especially handy when viewing geometries a small
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scales.
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</p>
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<p>
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OpenLayers.Geometry.LineString::simplify is a recursive
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implementation of the famous Douglas-Peucker algorithm. It is
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controlled by a tolerance factor that defines the threshold for
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vertices to be considered "insignificant" for the
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general structure of the geometry.
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</p>
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<p>
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The LineString on the left map can be simplified according to
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the tolerance value one enters in the form-field above the maps.
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Use a value between 0 and 1 for best results. If you navigate
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the left map, the right map will show the same location to make
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it easier to spot the differeces between the LineStrings.
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</p>
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<p>
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You can also use the button "Start animation" to get
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results for increasing tolerance-factors from 0.02 to 1.0. The
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animation can be paused by clicking on the button "Stop
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animation".
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</p>
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<p>
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The LineString represents a part of the coastline of
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<a href="http://www.openstreetmap.org/?lat=54.7309684753418&lon=83.1809234619141&zoom=11">this
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place southeast of Novosibirsk in Russia</a> — found via
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<a href="http://ryba4.com/python/ramer-douglas-peucker">an
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example implementation of the algorithm in python</a>.
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</p>
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<p>
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For a detailled explanation of the algorithm see
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<a href="http://en.wikipedia.org/wiki/Douglas-Peucker_algorithm">the
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Wikipedia article</a> or the original publication: David Douglas
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& Thomas Peucker, "Algorithms for the reduction of the
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number of points required to represent a digitized line or its
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caricature", The Canadian Cartographer 10(2), 112-122 (1973)
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(<a href="http://dx.doi.org/10.3138/FM57-6770-U75U-7727">DOI:
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10.3138/FM57-6770-U75U-7727</a>).
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</p>
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<p>See <a href="simplify-linestring.js">simplify-linestring.js</a>
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for the source code of this example.</p>
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</div>
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<script type="text/javascript" src="../lib/OpenLayers.js">
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</script>
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<script type="text/javascript" src="./simplify-linestring.js">
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</script>
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</body>
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</html>
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