[OpenLayers-Commits] r10969 - in trunk/openlayers: examples
lib/OpenLayers/Geometry tests/Geometry
commits-20090109 at openlayers.org
commits-20090109 at openlayers.org
Wed Dec 15 08:38:52 EST 2010
Author: ahocevar
Date: 2010-12-15 05:38:52 -0800 (Wed, 15 Dec 2010)
New Revision: 10969
Added:
trunk/openlayers/examples/simplify-linestring.html
trunk/openlayers/examples/simplify-linestring.js
Modified:
trunk/openlayers/lib/OpenLayers/Geometry/LineString.js
trunk/openlayers/tests/Geometry/LineString.html
Log:
Added Douglas-Peucker linestring simplification to OpenLayers.Geometry.LineString. Thanks chrismayer for this excellent patch. p=chrismayer, r=me (closes #2869)
Added: trunk/openlayers/examples/simplify-linestring.html
===================================================================
--- trunk/openlayers/examples/simplify-linestring.html (rev 0)
+++ trunk/openlayers/examples/simplify-linestring.html 2010-12-15 13:38:52 UTC (rev 10969)
@@ -0,0 +1,86 @@
+<!DOCTYPE html>
+<html>
+ <head>
+ <title>Simplify LineString</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;
+ }
+ </style>
+ </head>
+ <body>
+ <h1 id="title">Simplify a LineString</h1>
+ <div id="tags">
+ Douglas-Peucker, Douglas, Peucker, Peuker, tolerance
+ </div>
+ <p id="shortdesc">
+ Shows the usage of the utility method "simplifyLineString" that
+ implements the Douglas-Peucker algorithm to remove "insignificant"
+ vertices from LineString geometries.
+ </p>
+ <div id="control-simplify">
+ <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" style="clear: both;">
+ <p>
+ The method OpenLayers.Util.simplifyLineString 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.Util.simplifyLineString 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 "insignificant" 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>
+ The LineString
+ represents a part of the coastline of
+ <a href="http://www.openstreetmap.org/?lat=54.7309684753418&lon=83.1809234619141&zoom=11">this
+ place in Russia</a> — 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
+ & 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>
+ </div>
+ <script type="text/javascript" src="../lib/OpenLayers.js">
+ </script>
+ <script type="text/javascript" src="simplify-linestring.js">
+ </script>
+ </body>
+</html>
Added: trunk/openlayers/examples/simplify-linestring.js
===================================================================
--- trunk/openlayers/examples/simplify-linestring.js (rev 0)
+++ trunk/openlayers/examples/simplify-linestring.js 2010-12-15 13:38:52 UTC (rev 10969)
@@ -0,0 +1,599 @@
+// global variables
+var map, map2;
+
+// wrap the instanciation code in an anonymous function that gets executed
+// immedeately
+(function(){
+ // style the vectorlayer
+ var styleMap = new OpenLayers.StyleMap({
+ 'default': new OpenLayers.Style({
+ strokeColor: "#333333",
+ strokeWidth: 1.2,
+ strokeOpacity: 1
+ })
+ });
+
+ // the vectorlayer
+ var vectorlayer = new OpenLayers.Layer.Vector('Vectorlayer', {
+ isBaseLayer: true,
+ styleMap: styleMap
+ });
+
+ var original = OpenLayers.Geometry.fromWKT("LINESTRING(" +
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+ "2.092758 8.929811," +
+ "2.148090 8.928756," +
+ "2.168397 8.937878," +
+ "2.146421 8.965533," +
+ "2.182173 8.943933," +
+ "2.201537 8.951311," +
+ "2.239138 8.938400," +
+ "2.267063 8.944989," +
+ "2.284939 8.925767," +
+ "2.306887 8.926022," +
+ "2.311086 8.936356," +
+ "2.296312 8.952489," +
+ "2.317254 8.981122," +
+ "2.334939 9.003844," +
+ "2.374500 9.014044," +
+ "2.386136 9.034778," +
+ "2.401962 9.044656," +
+ "2.418723 9.044889," +
+ "2.426287 9.054878," +
+ "2.411739 9.063522," +
+ "2.426867 9.099311," +
+ "2.398362 9.125233," +
+ "2.373339 9.121944," +
+ "2.403595 9.134289," +
+ "2.417680 9.165778," +
+ "2.425860 9.192778," +
+ "2.423783 9.231400," +
+ "2.400330 9.237022," +
+ "2.419494 9.243567," +
+ "2.429815 9.246711," +
+ "2.449495 9.245489," +
+ "2.457676 9.289856," +
+ "2.481311 9.298211," +
+ "2.488585 9.334211," +
+ "2.520255 9.353822," +
+ "2.520400 9.369944," +
+ "2.494960 9.432511," +
+ "2.463671 9.469200," +
+ "2.406950 9.500578," +
+ "2.240907 9.536433," +
+ "2.129969 9.569467," +
+ "2.031530 9.607422," +
+ "1.932328 9.658044," +
+ "1.835167 9.695656," +
+ "1.746196 9.760744," +
+ "1.667446 9.789667," +
+ "1.575400 9.797622," +
+ "1.562104 9.828722," +
+ "1.531422 9.846800," +
+ "1.415859 9.888744," +
+ "1.315206 9.942167," +
+ "1.175573 10.083667," +
+ "1.147394 10.090267," +
+ "1.118064 10.086567," +
+ "0.990883 9.998400," +
+ "0.778930 9.990856," +
+ "0.592924 10.033144," +
+ "0.507490 10.125422," +
+ "0.419562 10.320811," +
+ "0.375403 10.344533," +
+ "0.276464 10.431189," +
+ "0.220170 10.534911," +
+ "0.181271 10.571000," +
+ "0.153745 10.620156," +
+ "0.114973 10.653889," +
+ "0.103274 10.707756," +
+ "0.097914 10.761511," +
+ "0.076256 10.811522," +
+ "0.061935 10.867833," +
+ "0.000000 10.960167)"
+ );
+ vectorlayer.addFeatures([new OpenLayers.Feature.Vector(original)]);
+ var maxExtent = vectorlayer.getDataExtent();
+ // instanciate the map
+ map = new OpenLayers.Map("map", {
+ fractionalZoom: true,
+ maxExtent: maxExtent,
+ layers: [vectorlayer]
+ });
+ map.zoomToMaxExtent();
+ map.events.register('moveend', map, function(){
+ map2.setCenter(map.getCenter(), map.getZoom());
+ });
+
+
+ var vectorlayer2 = new OpenLayers.Layer.Vector('Vectorlayer simplified', {
+ isBaseLayer: true,
+ styleMap: styleMap
+ });
+
+ map2 = new OpenLayers.Map("map-simplify", {
+ fractionalZoom: true,
+ maxExtent: maxExtent,
+ controls: [],
+ layers: [vectorlayer2]
+ });
+ map2.zoomToExtent(maxExtent);
+
+ // Control behaviour
+ var lastValue = 0.1;
+ var simplify = function() {
+ var min = 0;
+ var max = 1;
+ var givenVal= parseFloat(document.getElementById('tolerance').value);
+ var useVal = lastValue;
+ if (!isNaN(givenVal)) {
+ if (givenVal >= min && givenVal <= max) {
+ useVal = givenVal;
+ } else {
+ useVal = (givenVal < min) ? min : max;
+ }
+ }
+ document.getElementById('tolerance').value = useVal;
+ vectorlayer2.removeFeatures(vectorlayer2.features);
+ var newLineString = original.simplify(useVal);
+ vectorlayer2.addFeatures([new OpenLayers.Feature.Vector(newLineString)]);
+ var originalVerticesCnt = original.getVertices().length;
+ var simplifiedVerticesCnt = newLineString.getVertices().length;
+ var infotxt = '<ul><li>Original LineString: <strong>';
+ infotxt += originalVerticesCnt + ' vertices</strong></li>';
+ infotxt += ' <li>Simplified geometry: <strong>' + simplifiedVerticesCnt + ' vertices</strong></li>';
+ infotxt += ' <li>Decreased by <strong>' + (((originalVerticesCnt-simplifiedVerticesCnt)/originalVerticesCnt)*100).toFixed(2) + ' per cent</strong></li></ul>';
+ document.getElementById('info').innerHTML = infotxt;
+ lastValue = useVal;
+ };
+ document.getElementById('tolerance').value = lastValue;
+ document.getElementById('simplify').onclick = simplify;
+ simplify();
+
+ var animationInterval;
+ var animationHandler = function(){
+ if (this.value === 'Start animation') {
+ document.getElementById('simplify').disabled = true;
+ document.getElementById('animation').value = "Stop animation";
+ animationInterval = window.setInterval(function(){
+ var tolerance = parseFloat(document.getElementById('tolerance').value);
+ if (tolerance < 1) {
+ tolerance+=0.02;
+ } else {
+ tolerance = 0.02;
+ }
+ document.getElementById('tolerance').value = tolerance.toFixed(2);
+ simplify();
+ }, 500);
+ simplify();
+ } else {
+ if (animationInterval) {
+ window.clearInterval(animationInterval);
+ }
+ document.getElementById('simplify').disabled = false;
+ document.getElementById('animation').value = "Start animation";
+ }
+ };
+ document.getElementById('animation').onclick = animationHandler;
+})();
Modified: trunk/openlayers/lib/OpenLayers/Geometry/LineString.js
===================================================================
--- trunk/openlayers/lib/OpenLayers/Geometry/LineString.js 2010-12-15 10:46:05 UTC (rev 10968)
+++ trunk/openlayers/lib/OpenLayers/Geometry/LineString.js 2010-12-15 13:38:52 UTC (rev 10969)
@@ -547,6 +547,98 @@
}
return best;
},
+
+ /**
+ * APIMethod: simplify
+ * This function will return a simplified LineString.
+ * Simplification is based on the Douglas-Peucker algorithm.
+ *
+ *
+ * Parameters:
+ * tolerance - {number} threshhold for simplification in map units
+ *
+ * Returns:
+ * {OpenLayers.Geometry.LineString} the simplified LineString
+ */
+ simplify: function(tolerance){
+ if (this && this !== null) {
+ var points = this.getVertices();
+ if (points.length < 3) {
+ return this;
+ }
+
+ var compareNumbers = function(a, b){
+ return (a-b);
+ };
+
+ /**
+ * Private function doing the Douglas-Peucker reduction
+ */
+ var douglasPeuckerReduction = function(points, firstPoint, lastPoint, tolerance){
+ var maxDistance = 0;
+ var indexFarthest = 0;
+
+ for (var index = firstPoint; index < lastPoint; index++) {
+ distance = perpendicularDistance(points[firstPoint], points[lastPoint], points[index]);
+ if (distance > maxDistance) {
+ maxDistance = distance;
+ indexFarthest = index;
+ }
+ }
+
+ if (maxDistance > tolerance && indexFarthest != firstPoint) {
+ //Add the largest point that exceeds the tolerance
+ pointIndexsToKeep.push(indexFarthest);
+ douglasPeuckerReduction(points, firstPoint, indexFarthest, tolerance);
+ douglasPeuckerReduction(points, indexFarthest, lastPoint, tolerance);
+ }
+ };
+
+ /**
+ * Private function calculating the perpendicular distance
+ * TODO: check whether OpenLayers.Geometry.LineString::distanceTo() is faster or slower
+ */
+ var perpendicularDistance = function(point1, point2, point){
+ //Area = |(1/2)(x1y2 + x2y3 + x3y1 - x2y1 - x3y2 - x1y3)| *Area of triangle
+ //Base = v((x1-x2)²+(x1-x2)²) *Base of Triangle*
+ //Area = .5*Base*H *Solve for height
+ //Height = Area/.5/Base
+
+ var area = Math.abs(0.5 * (point1.x * point2.y + point2.x * point.y + point.x * point1.y - point2.x * point1.y - point.x * point2.y - point1.x * point.y));
+ var bottom = Math.sqrt(Math.pow(point1.x - point2.x, 2) + Math.pow(point1.y - point2.y, 2));
+ var height = area / bottom * 2;
+
+ return height;
+ };
+
+ var firstPoint = 0;
+ var lastPoint = points.length - 1;
+ var pointIndexsToKeep = [];
+
+ //Add the first and last index to the keepers
+ pointIndexsToKeep.push(firstPoint);
+ pointIndexsToKeep.push(lastPoint);
+
+ //The first and the last point cannot be the same
+ while (points[firstPoint].equals(points[lastPoint])) {
+ lastPoint--;
+ //Addition: the first point not equal to first point in the LineString is kept as well
+ pointIndexsToKeep.push(lastPoint);
+ }
+
+ douglasPeuckerReduction(points, firstPoint, lastPoint, tolerance);
+ var returnPoints = [];
+ pointIndexsToKeep.sort(compareNumbers);
+ for (var index = 0; index < pointIndexsToKeep.length; index++) {
+ returnPoints.push(points[pointIndexsToKeep[index]]);
+ }
+ return new OpenLayers.Geometry.LineString(returnPoints);
+
+ }
+ else {
+ return this;
+ }
+ },
CLASS_NAME: "OpenLayers.Geometry.LineString"
});
Modified: trunk/openlayers/tests/Geometry/LineString.html
===================================================================
--- trunk/openlayers/tests/Geometry/LineString.html 2010-12-15 10:46:05 UTC (rev 10968)
+++ trunk/openlayers/tests/Geometry/LineString.html 2010-12-15 13:38:52 UTC (rev 10969)
@@ -374,7 +374,67 @@
t.eq(Math.round(got), Math.round(cases[i].exp), "[case " + i + "] length calculated");
}
- }
+ }
+
+ function test_LineString_simplify(t){
+ t.plan(8);
+ var ls1 = new OpenLayers.Geometry.LineString([
+ new OpenLayers.Geometry.Point(0,0),
+ new OpenLayers.Geometry.Point(1,2.1),
+ new OpenLayers.Geometry.Point(1.8,3.8),
+ new OpenLayers.Geometry.Point(2,4),
+ new OpenLayers.Geometry.Point(3,4),
+ new OpenLayers.Geometry.Point(4,4.5),
+ new OpenLayers.Geometry.Point(5,5)
+
+ ]);
+ var ls2 = new OpenLayers.Geometry.LineString([
+ new OpenLayers.Geometry.Point(0,0),
+ new OpenLayers.Geometry.Point(1,2.1),
+ new OpenLayers.Geometry.Point(1.8,3.8),
+ new OpenLayers.Geometry.Point(2,4),
+ new OpenLayers.Geometry.Point(3,4),
+ new OpenLayers.Geometry.Point(4,4.5),
+ new OpenLayers.Geometry.Point(5,5),
+ new OpenLayers.Geometry.Point(0,0)
+
+ ]);
+ var ls3 = new OpenLayers.Geometry.LineString([
+ new OpenLayers.Geometry.Point(0,0),
+ new OpenLayers.Geometry.Point(1,1)
+ ]);
+ var ls5 = new OpenLayers.Geometry.LineString([
+ new OpenLayers.Geometry.Point(0,0),
+ new OpenLayers.Geometry.Point(1,1),
+ new OpenLayers.Geometry.Point(2,2),
+ new OpenLayers.Geometry.Point(3,3),
+ new OpenLayers.Geometry.Point(4,4),
+ new OpenLayers.Geometry.Point(5,5)
+
+ ]);
+ var ls6 = new OpenLayers.Geometry.LineString([
+ new OpenLayers.Geometry.Point(0,0),
+ new OpenLayers.Geometry.Point(1,1),
+ new OpenLayers.Geometry.Point(1,1),
+ new OpenLayers.Geometry.Point(3,2)
+ ]);
+
+ t.ok(ls1 instanceof OpenLayers.Geometry.LineString, 'LineString is instance of OpenLayers.Geometry.LineString');
+ var simplified1 = ls1.simplify(0.5);
+ t.ok(simplified1 instanceof OpenLayers.Geometry.LineString, 'Simplified LineString is instance of OpenLayers.Geometry.LineString');
+ t.ok(simplified1.getVertices().length <= ls1.getVertices().length, 'Simplified LineString has less or equal number of vertices');
+ // The simplified version is derived from PostGIS function ST_SIMPLIFY()
+ t.ok(simplified1.toString() === 'LINESTRING(0 0,1.8 3.8,5 5)', 'LineString 1 was simplified correctly');
+ var simplified2 = ls2.simplify(0.5);
+ // The simplified version is derived from PostGIS function ST_SIMPLIFY()
+ t.ok(simplified2.toString() === 'LINESTRING(0 0,1.8 3.8,5 5,0 0)', 'LineString 2 was simplified correctly');
+ var simplified3 = ls3.simplify(0.5);
+ t.ok(simplified3.toString() === ls3.toString(), 'LineString with 2 vertices is left untouched');
+ var simplified5 = ls5.simplify(0.0);
+ t.ok(simplified5.toString() === 'LINESTRING(0 0,5 5)', 'A tolerance of 0 returns the optimized version needless vertices');
+ var simplified6 = ls6.simplify(0.0);
+ t.ok(simplified6.toString() === 'LINESTRING(0 0,1 1,3 2)', 'A tolerance of 0 returns the optimized version without doubled vertices');
+ }
</script>
</head>
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