diff --git a/examples/measure.html b/examples/measure.html index 9a4285f5ee..ec671284d9 100644 --- a/examples/measure.html +++ b/examples/measure.html @@ -64,12 +64,13 @@ measureControls = { line: new OpenLayers.Control.Measure( - OpenLayers.Handler.Path, { - persist: true, - handlerOptions: { - layerOptions: {styleMap: styleMap}, + OpenLayers.Handler.Path, { + persist: true, + handlerOptions: { + layerOptions: {styleMap: styleMap} + } } - }), + ), polygon: new OpenLayers.Control.Measure( OpenLayers.Handler.Polygon, { persist: true, @@ -94,31 +95,6 @@ document.getElementById('noneToggle').checked = true; } - - function calcVincenty(geometry) { - /** - * Note: this function assumes geographic coordinates and - * will fail otherwise. OpenLayers.Util.distVincenty takes - * two objects representing points with geographic coordinates - * and returns the geodesic distance between them (shortest - * distance between the two points on an ellipsoid) in *kilometers*. - * - * It is important to realize that the segments drawn on the map - * are *not* geodesics (or "great circle" segments). This means - * that in general, the measure returned by this function - * will not represent the length of segments drawn on the map. - */ - var dist = 0; - for (var i = 1; i < geometry.components.length; i++) { - var first = geometry.components[i-1]; - var second = geometry.components[i]; - dist += OpenLayers.Util.distVincenty( - {lon: first.x, lat: first.y}, - {lon: second.x, lat: second.y} - ); - } - return dist; - } function handleMeasurements(event) { var geometry = event.geometry; @@ -129,10 +105,6 @@ var out = ""; if(order == 1) { out += "measure: " + measure.toFixed(3) + " " + units; - if (map.getProjection() == "EPSG:4326") { - out += "
Great Circle Distance: " + - calcVincenty(geometry).toFixed(3) + " km *"; - } } else { out += "measure: " + measure.toFixed(3) + " " + units + "2"; } @@ -149,6 +121,13 @@ } } } + + function toggleGeodesic(element) { + for(key in measureControls) { + var control = measureControls[key]; + control.geodesic = element.checked; + } + } @@ -174,13 +153,17 @@ +
  • + + +
    • -

    * Note that the geometries drawn are planar geometries and the - metrics returned by the measure control are planar measures. The - "great circle" distance does not necessarily represent the length - of the segments drawn on the map. Instead, it is a geodesic metric that - represents the cumulative shortest path between all vertices in the - geometry were they projected onto a sphere.

    +

    Note that the geometries drawn are planar geometries and the + metrics returned by the measure control are planar measures by + default. If your map is in a geographic projection or you have the + appropriate projection definitions to transform your geometries into + geographic coordinates, you can set the "geodesic" property of the control + to true to calculate geodesic measures instead of planar measures.

    diff --git a/lib/OpenLayers/Control/Measure.js b/lib/OpenLayers/Control/Measure.js index 88b712be7d..caa72f5e0f 100644 --- a/lib/OpenLayers/Control/Measure.js +++ b/lib/OpenLayers/Control/Measure.js @@ -56,6 +56,14 @@ OpenLayers.Control.Measure = OpenLayers.Class(OpenLayers.Control, { */ displaySystem: 'metric', + /** + * Property: geodesic + * {Boolean} Calculate geodesic metrics instead of planar metrics. This + * requires that geometries can be transformed into Geographic/WGS84 + * (if that is not already the map projection). Default is false. + */ + geodesic: false, + /** * Property: displaySystemUnits * {Object} Units for various measurement systems. Values are arrays @@ -213,10 +221,17 @@ OpenLayers.Control.Measure = OpenLayers.Class(OpenLayers.Control, { * {Float} The geometry area in the given units. */ getArea: function(geometry, units) { - var area = geometry.getArea(); + var area, geomUnits; + if(this.geodesic) { + area = geometry.getGeodesicArea(this.map.getProjectionObject()); + geomUnits = "m"; + } else { + area = geometry.getArea(); + geomUnits = this.map.getUnits(); + } var inPerDisplayUnit = OpenLayers.INCHES_PER_UNIT[units]; if(inPerDisplayUnit) { - var inPerMapUnit = OpenLayers.INCHES_PER_UNIT[this.map.getUnits()]; + var inPerMapUnit = OpenLayers.INCHES_PER_UNIT[geomUnits]; area *= Math.pow((inPerMapUnit / inPerDisplayUnit), 2); } return area; @@ -257,10 +272,17 @@ OpenLayers.Control.Measure = OpenLayers.Class(OpenLayers.Control, { * {Float} The geometry length in the given units. */ getLength: function(geometry, units) { - var length = geometry.getLength(); + var length, geomUnits; + if(this.geodesic) { + length = geometry.getGeodesicLength(this.map.getProjectionObject()); + geomUnits = "m"; + } else { + length = geometry.getLength(); + geomUnits = this.map.getUnits(); + } var inPerDisplayUnit = OpenLayers.INCHES_PER_UNIT[units]; if(inPerDisplayUnit) { - var inPerMapUnit = OpenLayers.INCHES_PER_UNIT[this.map.getUnits()]; + var inPerMapUnit = OpenLayers.INCHES_PER_UNIT[geomUnits]; length *= (inPerMapUnit / inPerDisplayUnit); } return length; diff --git a/lib/OpenLayers/Geometry/Collection.js b/lib/OpenLayers/Geometry/Collection.js index 116da965df..05868d3a70 100644 --- a/lib/OpenLayers/Geometry/Collection.js +++ b/lib/OpenLayers/Geometry/Collection.js @@ -231,6 +231,52 @@ OpenLayers.Geometry.Collection = OpenLayers.Class(OpenLayers.Geometry, { return area; }, + /** + * APIMethod: getGeodesicArea + * Calculate the approximate area of the polygon were it projected onto + * the earth. + * + * Parameters: + * projection - {} The spatial reference system + * for the geometry coordinates. If not provided, Geographic/WGS84 is + * assumed. + * + * Reference: + * Robert. G. Chamberlain and William H. Duquette, "Some Algorithms for + * Polygons on a Sphere", JPL Publication 07-03, Jet Propulsion + * Laboratory, Pasadena, CA, June 2007 http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409 + * + * Returns: + * {float} The approximate geodesic area of the geometry in square meters. + */ + getGeodesicArea: function(projection) { + var area = 0.0; + for(var i=0, len=this.components.length; i} The spatial reference system + * for the geometry coordinates. If not provided, Geographic/WGS84 is + * assumed. + * + * Returns: + * {Float} The appoximate geodesic length of the geometry in meters. + */ + getGeodesicLength: function(projection) { + var length = 0.0; + for(var i=0, len=this.components.length; i} The spatial reference system + * for the geometry coordinates. If not provided, Geographic/WGS84 is + * assumed. + * + * Returns: + * {Float} The appoximate geodesic length of the geometry in meters. + */ + getGeodesicLength: function(projection) { + var geom = this; // so we can work with a clone if needed + if(projection) { + var gg = new OpenLayers.Projection("EPSG:4326"); + if(!gg.equals(projection)) { + geom = this.clone().transform(projection, gg); + } + } + var length = 0.0; + if(geom.components && (geom.components.length > 1)) { + var p1, p2; + for(var i=1, len=geom.components.length; i} The spatial reference system + * for the geometry coordinates. If not provided, Geographic/WGS84 is + * assumed. + * + * Reference: + * Robert. G. Chamberlain and William H. Duquette, "Some Algorithms for + * Polygons on a Sphere", JPL Publication 07-03, Jet Propulsion + * Laboratory, Pasadena, CA, June 2007 http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409 + * + * Returns: + * {float} The approximate signed geodesic area of the polygon in square + * meters. + */ + getGeodesicArea: function(projection) { + var ring = this; // so we can work with a clone if needed + if(projection) { + var gg = new OpenLayers.Projection("EPSG:4326"); + if(!gg.equals(projection)) { + ring = this.clone().transform(projection, gg); + } + } + var area = 0.0; + var len = ring.components && ring.components.length; + if(len > 2) { + var p1, p2; + for(var i=0; i} The spatial reference system + * for the geometry coordinates. If not provided, Geographic/WGS84 is + * assumed. + * + * Reference: + * Robert. G. Chamberlain and William H. Duquette, "Some Algorithms for + * Polygons on a Sphere", JPL Publication 07-03, Jet Propulsion + * Laboratory, Pasadena, CA, June 2007 http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409 + * + * Returns: + * {float} The approximate geodesic area of the polygon in square meters. + */ + getGeodesicArea: function(projection) { + var area = 0.0; + if(this.components && (this.components.length > 0)) { + area += Math.abs(this.components[0].getGeodesicArea(projection)); + for(var i=1, len=this.components.length; i diff --git a/tests/Geometry/Polygon.html b/tests/Geometry/Polygon.html index 8eccbc5503..2a5fb361b0 100644 --- a/tests/Geometry/Polygon.html +++ b/tests/Geometry/Polygon.html @@ -350,6 +350,29 @@ t.ok(geometry.equals(clone), "clone has equivalent coordinates"); } + function test_getGeodesicArea(t) { + + t.plan(1); + + // from the wfs-states.html example + var illinois = OpenLayers.Geometry.fromWKT( + "MULTIPOLYGON(((-88.071564 37.51099,-88.087883 37.476273,-88.311707 37.442852,-88.359177 37.409309,-88.419853 37.420292,-88.467644 37.400757,-88.511322 37.296852,-88.501427 37.257782,-88.450699 37.205669,-88.422516 37.15691,-88.45047 37.098671,-88.476799 37.072144,-88.4907 37.06818,-88.517273 37.06477,-88.559273 37.072815,-88.61422 37.109047,-88.68837 37.13541,-88.739113 37.141182,-88.746506 37.152107,-88.863289 37.202194,-88.932503 37.218407,-88.993172 37.220036,-89.065033 37.18586,-89.116821 37.112137,-89.146347 37.093185,-89.169548 37.064236,-89.174332 37.025711,-89.150246 36.99844,-89.12986 36.988113,-89.193512 36.986771,-89.210052 37.028973,-89.237679 37.041733,-89.264053 37.087124,-89.284233 37.091244,-89.303291 37.085384,-89.3097 37.060909,-89.264244 37.027733,-89.262001 37.008686,-89.282768 36.999207,-89.310982 37.009682,-89.38295 37.049213,-89.37999 37.099083,-89.423798 37.137203,-89.440521 37.165318,-89.468216 37.224266,-89.465309 37.253731,-89.489594 37.256001,-89.513885 37.276402,-89.513885 37.304962,-89.50058 37.329441,-89.468742 37.339409,-89.435738 37.355717,-89.427574 37.411018,-89.453621 37.453186,-89.494781 37.491726,-89.524971 37.571957,-89.513367 37.615929,-89.51918 37.650375,-89.513374 37.67984,-89.521523 37.694798,-89.581436 37.706104,-89.666458 37.745453,-89.675858 37.78397,-89.691055 37.804794,-89.728447 37.840992,-89.851715 37.905064,-89.861046 37.905487,-89.866814 37.891876,-89.900551 37.875904,-89.937874 37.878044,-89.978912 37.911884,-89.958229 37.963634,-90.010811 37.969318,-90.041924 37.993206,-90.119339 38.032272,-90.134712 38.053951,-90.207527 38.088905,-90.254059 38.122169,-90.289635 38.166817,-90.336716 38.188713,-90.364769 38.234299,-90.369347 38.323559,-90.358688 38.36533,-90.339607 38.390846,-90.301842 38.427357,-90.265785 38.518688,-90.26123 38.532768,-90.240944 38.562805,-90.183708 38.610271,-90.183578 38.658772,-90.20224 38.700363,-90.196571 38.723965,-90.163399 38.773098,-90.135178 38.785484,-90.121727 38.80051,-90.113121 38.830467,-90.132812 38.853031,-90.243927 38.914509,-90.278931 38.924717,-90.31974 38.924908,-90.413071 38.96233,-90.469841 38.959179,-90.530426 38.891609,-90.570328 38.871326,-90.627213 38.880795,-90.668877 38.935253,-90.70607 39.037792,-90.707588 39.058178,-90.690399 39.0937,-90.716736 39.144211,-90.718193 39.195873,-90.732338 39.224747,-90.738083 39.24781,-90.779343 39.296803,-90.850494 39.350452,-90.947891 39.400585,-91.036339 39.444412,-91.064384 39.473984,-91.093613 39.528927,-91.156189 39.552593,-91.203247 39.600021,-91.317665 39.685917,-91.367088 39.72464,-91.373421 39.761272,-91.381714 39.803772,-91.449188 39.863049,-91.450989 39.885242,-91.434052 39.901829,-91.430389 39.921837,-91.447243 39.946064,-91.487289 40.005753,-91.504005 40.066711,-91.516129 40.134544,-91.506546 40.200459,-91.498932 40.251377,-91.486694 40.309624,-91.448593 40.371902,-91.418816 40.386875,-91.385757 40.392361,-91.372757 40.402988,-91.385399 40.44725,-91.374794 40.503654,-91.382103 40.528496,-91.412872 40.547993,-91.411118 40.572971,-91.37561 40.603439,-91.262062 40.639545,-91.214912 40.643818,-91.162498 40.656311,-91.129158 40.682148,-91.119987 40.705402,-91.092751 40.761547,-91.088905 40.833729,-91.04921 40.879585,-90.983276 40.923927,-90.960709 40.950504,-90.954651 41.070362,-90.957787 41.104359,-90.990341 41.144371,-91.018257 41.165825,-91.05632 41.176258,-91.101524 41.231522,-91.102348 41.267818,-91.07328 41.334896,-91.055786 41.401379,-91.027489 41.423508,-91.000694 41.431084,-90.949654 41.421234,-90.844139 41.444622,-90.7799 41.449821,-90.708214 41.450062,-90.658791 41.462318,-90.6007 41.509586,-90.54084 41.52597,-90.454994 41.527546,-90.434967 41.543579,-90.423004 41.567272,-90.348366 41.586849,-90.339348 41.602798,-90.341133 41.64909,-90.326027 41.722736,-90.304886 41.756466,-90.25531 41.781738,-90.195839 41.806137,-90.154518 41.930775,-90.14267 41.983963,-90.150536 42.033428,-90.168098 42.061043,-90.166649 42.103745,-90.176086 42.120502,-90.191574 42.122688,-90.230934 42.159721,-90.323601 42.197319,-90.367729 42.210209,-90.407173 42.242645,-90.417984 42.263924,-90.427681 42.340633,-90.441597 42.360073,-90.491043 42.388783,-90.563583 42.421837,-90.605827 42.46056,-90.648346 42.475643,-90.651772 42.494698,-90.638329 42.509361,-90.419975 42.508362,-89.923569 42.504108,-89.834618 42.50346,-89.400497 42.49749,-89.359444 42.497906,-88.939079 42.490864,-88.764954 42.490906,-88.70652 42.489655,-88.297897 42.49197,-88.194702 42.489613,-87.79731 42.489132,-87.836945 42.314213,-87.760239 42.156456,-87.670547 42.059822,-87.612625 41.847332,-87.529861 41.723591,-87.532646 41.469715,-87.532448 41.301304,-87.531731 41.173756,-87.532021 41.00993,-87.532669 40.745411,-87.53717 40.49461,-87.535675 40.483246,-87.535339 40.166195,-87.535774 39.887302,-87.535576 39.609341,-87.538567 39.477448,-87.540215 39.350525,-87.597664 39.338268,-87.625237 39.307404,-87.610619 39.297661,-87.615799 39.281418,-87.606895 39.258163,-87.584564 39.248753,-87.588593 39.208466,-87.594208 39.198128,-87.607925 39.196068,-87.644257 39.168507,-87.670326 39.146679,-87.659454 39.130653,-87.662262 39.113468,-87.631668 39.103943,-87.630867 39.088974,-87.612007 39.084606,-87.58532 39.062435,-87.581749 38.995743,-87.591858 38.994083,-87.547905 38.977077,-87.53347 38.963703,-87.530182 38.931919,-87.5392 38.904861,-87.559059 38.869812,-87.550507 38.857891,-87.507889 38.795559,-87.519028 38.776699,-87.508003 38.769722,-87.508316 38.736633,-87.543892 38.685974,-87.588478 38.672169,-87.625191 38.642811,-87.628647 38.622917,-87.619827 38.599209,-87.640594 38.593178,-87.652855 38.573872,-87.672943 38.547424,-87.65139 38.515369,-87.653534 38.500443,-87.679909 38.504005,-87.692818 38.481533,-87.756096 38.466125,-87.758659 38.457096,-87.738953 38.44548,-87.748428 38.417965,-87.784019 38.378124,-87.834503 38.352524,-87.850082 38.286098,-87.863007 38.285362,-87.874039 38.316788,-87.883446 38.315552,-87.888466 38.300659,-87.914108 38.281048,-87.913651 38.302345,-87.925919 38.304771,-87.980019 38.241085,-87.986008 38.234814,-87.977928 38.200714,-87.932289 38.171131,-87.931992 38.157528,-87.950569 38.136913,-87.973503 38.13176,-88.018547 38.103302,-88.012329 38.092346,-87.964867 38.096748,-87.975296 38.073307,-88.034729 38.054085,-88.043091 38.04512,-88.041473 38.038303,-88.021698 38.033531,-88.029213 38.008236,-88.021706 37.975056,-88.042511 37.956264,-88.041771 37.934498,-88.064621 37.929783,-88.078941 37.944,-88.084 37.92366,-88.030441 37.917591,-88.026588 37.905758,-88.044868 37.896004,-88.100082 37.90617,-88.101456 37.895306,-88.075737 37.867809,-88.034241 37.843746,-88.042137 37.827522,-88.089264 37.831249,-88.086029 37.817612,-88.035576 37.805683,-88.072472 37.735401,-88.133636 37.700745,-88.15937 37.660686,-88.157631 37.628479,-88.134171 37.583572,-88.071564 37.51099)))" + ); + + // two calculations of the area (in square meters) + var planar = illinois.getArea() * Math.pow(OpenLayers.INCHES_PER_UNIT['dd'] / OpenLayers.INCHES_PER_UNIT['m'], 2); + var geodesic = illinois.getGeodesicArea(); + + // from http://en.wikipedia.org/wiki/Illinois + var expected = 1.40998e11; // square meters + + var planarErr = Math.abs(planar - expected) / expected; + var geodesicErr = Math.abs(geodesic - expected) / expected; + + t.ok(geodesicErr < planarErr, "geodesic measure is better (" + geodesicErr.toFixed(3) + " vs. " + planarErr.toFixed(3) + ")"); + + } +