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Adding methods for getting geodesic measures from geometries. Assuming geometries can be transformed into Geographic/WGS84, getGeodesicLength and getGeodesicArea should return reasonable 'on the ground' metrics. Use getLength and getArea for the planar metrics. r=crschmidt (closes #1819)

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git-svn-id: http://svn.openlayers.org/trunk/openlayers@9248 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf
This commit is contained in:
Tim Schaub
2009-04-08 23:12:24 +00:00
parent 5f335f4207
commit 08077f0f42
8 changed files with 250 additions and 44 deletions
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63
examples/measure.html
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@@ -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 += "<br /> Great Circle Distance: " +
calcVincenty(geometry).toFixed(3) + " km *";
}
} else {
out += "measure: " + measure.toFixed(3) + " " + units + "<sup>2</" + "sup>";
}
@@ -149,6 +121,13 @@
}
}
}
function toggleGeodesic(element) {
for(key in measureControls) {
var control = measureControls[key];
control.geodesic = element.checked;
}
}
</script>
</head>
<body onload="init()">
@@ -174,13 +153,17 @@
<input type="radio" name="type" value="polygon" id="polygonToggle" onclick="toggleControl(this);" />
<label for="polygonToggle">measure area</label>
</li>
<li>
<input type="checkbox" name="geodesic" id="geodesicToggle" onclick="toggleGeodesic(this);" />
<label for="polygonToggle">use geodesic measures</label>
</li>
</ul>
<p>* 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.</p>
<p>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.</p>
</div>
</body>
</html>