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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)

Browse Source 
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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30
lib/OpenLayers/Control/Measure.js
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@@ -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;

46
lib/OpenLayers/Geometry/Collection.js
View File

@@ -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 - {<OpenLayers.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<len; i++) {
area += this.components[i].getGeodesicArea(projection);
}
return area;
},
/**
* APIMethod: getGeodesicLength
* Calculate the approximate length of the geometry were it projected onto
* the earth.
*
* projection - {<OpenLayers.Projection>} 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<len; i++) {
length += this.components[i].getGeodesicLength(projection);
}
return length;
},
/**
* APIMethod: move
* Moves a geometry by the given displacement along positive x and y axes.

36
lib/OpenLayers/Geometry/Curve.js
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@@ -52,5 +52,41 @@ OpenLayers.Geometry.Curve = OpenLayers.Class(OpenLayers.Geometry.MultiPoint, {
return length;
},
/**
* APIMethod: getGeodesicLength
* Calculate the approximate length of the geometry were it projected onto
* the earth.
*
* projection - {<OpenLayers.Projection>} 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<len; i++) {
p1 = geom.components[i-1];
p2 = geom.components[i];
// this returns km and requires lon/lat properties
length += OpenLayers.Util.distVincenty(
{lon: p1.x, lat: p1.y}, {lon: p2.x, lat: p2.y}
);
}
}
// convert to m
return length * 1000;
},
CLASS_NAME: "OpenLayers.Geometry.Curve"
});

44
lib/OpenLayers/Geometry/LinearRing.js
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@@ -205,6 +205,50 @@ OpenLayers.Geometry.LinearRing = OpenLayers.Class(
return area;
},
/**
* APIMethod: getGeodesicArea
* Calculate the approximate area of the polygon were it projected onto
* the earth. Note that this area will be positive if ring is oriented
* clockwise, otherwise it will be negative.
*
* Parameters:
* projection - {<OpenLayers.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 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<len-1; i++) {
p1 = ring.components[i];
p2 = ring.components[i+1];
area += OpenLayers.Util.rad(p2.x - p1.x) *
(2 + Math.sin(OpenLayers.Util.rad(p1.y)) +
Math.sin(OpenLayers.Util.rad(p2.y)));
}
area = area * 6378137.0 * 6378137.0 / 2.0;
}
return area;
},
/**
* Method: containsPoint
* Test if a point is inside a linear ring. For the case where a point

29
lib/OpenLayers/Geometry/Polygon.js
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@@ -60,6 +60,35 @@ OpenLayers.Geometry.Polygon = OpenLayers.Class(
return area;
},
/**
* APIMethod: getGeodesicArea
* Calculate the approximate area of the polygon were it projected onto
* the earth.
*
* Parameters:
* projection - {<OpenLayers.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 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<len; i++) {
area -= Math.abs(this.components[i].getGeodesicArea(projection));
}
}
return area;
},
/**
* Method: containsPoint
* Test if a point is inside a polygon. Points on a polygon edge are