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Filename : Polygon.js
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/* Copyright (c) 2006-2013 by OpenLayers Contributors (see authors.txt for
 * full list of contributors). Published under the 2-clause BSD license.
 * See license.txt in the OpenLayers distribution or repository for the
 * full text of the license. */

/**
 * @requires OpenLayers/Geometry/Collection.js
 * @requires OpenLayers/Geometry/LinearRing.js
 */

/**
 * Class: OpenLayers.Geometry.Polygon 
 * Polygon is a collection of Geometry.LinearRings. 
 * 
 * Inherits from:
 *  - <OpenLayers.Geometry.Collection> 
 *  - <OpenLayers.Geometry> 
 */
OpenLayers.Geometry.Polygon = OpenLayers.Class(
  OpenLayers.Geometry.Collection, {

    /**
     * Property: componentTypes
     * {Array(String)} An array of class names representing the types of
     * components that the collection can include.  A null value means the
     * component types are not restricted.
     */
    componentTypes: ["OpenLayers.Geometry.LinearRing"],

    /**
     * Constructor: OpenLayers.Geometry.Polygon
     * Constructor for a Polygon geometry. 
     * The first ring (this.component[0])is the outer bounds of the polygon and 
     * all subsequent rings (this.component[1-n]) are internal holes.
     *
     *
     * Parameters:
     * components - {Array(<OpenLayers.Geometry.LinearRing>)} 
     */

    /** 
     * APIMethod: getArea
     * Calculated by subtracting the areas of the internal holes from the 
     *   area of the outer hole.
     * 
     * Returns:
     * {float} The area of the geometry
     */
    getArea: function() {
        var area = 0.0;
        if ( this.components && (this.components.length > 0)) {
            area += Math.abs(this.components[0].getArea());
            for (var i=1, len=this.components.length; i<len; i++) {
                area -= Math.abs(this.components[i].getArea());
            }
        }
        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
     *     considered inside.
     *
     * Parameters:
     * point - {<OpenLayers.Geometry.Point>}
     *
     * Returns:
     * {Boolean | Number} The point is inside the polygon.  Returns 1 if the
     *     point is on an edge.  Returns boolean otherwise.
     */
    containsPoint: function(point) {
        var numRings = this.components.length;
        var contained = false;
        if(numRings > 0) {
            // check exterior ring - 1 means on edge, boolean otherwise
            contained = this.components[0].containsPoint(point);
            if(contained !== 1) {
                if(contained && numRings > 1) {
                    // check interior rings
                    var hole;
                    for(var i=1; i<numRings; ++i) {
                        hole = this.components[i].containsPoint(point);
                        if(hole) {
                            if(hole === 1) {
                                // on edge
                                contained = 1;
                            } else {
                                // in hole
                                contained = false;
                            }                            
                            break;
                        }
                    }
                }
            }
        }
        return contained;
    },

    /**
     * APIMethod: intersects
     * Determine if the input geometry intersects this one.
     *
     * Parameters:
     * geometry - {<OpenLayers.Geometry>} Any type of geometry.
     *
     * Returns:
     * {Boolean} The input geometry intersects this one.
     */
    intersects: function(geometry) {
        var intersect = false;
        var i, len;
        if(geometry.CLASS_NAME == "OpenLayers.Geometry.Point") {
            intersect = this.containsPoint(geometry);
        } else if(geometry.CLASS_NAME == "OpenLayers.Geometry.LineString" ||
                  geometry.CLASS_NAME == "OpenLayers.Geometry.LinearRing") {
            // check if rings/linestrings intersect
            for(i=0, len=this.components.length; i<len; ++i) {
                intersect = geometry.intersects(this.components[i]);
                if(intersect) {
                    break;
                }
            }
            if(!intersect) {
                // check if this poly contains points of the ring/linestring
                for(i=0, len=geometry.components.length; i<len; ++i) {
                    intersect = this.containsPoint(geometry.components[i]);
                    if(intersect) {
                        break;
                    }
                }
            }
        } else {
            for(i=0, len=geometry.components.length; i<len; ++ i) {
                intersect = this.intersects(geometry.components[i]);
                if(intersect) {
                    break;
                }
            }
        }
        // check case where this poly is wholly contained by another
        if(!intersect && geometry.CLASS_NAME == "OpenLayers.Geometry.Polygon") {
            // exterior ring points will be contained in the other geometry
            var ring = this.components[0];
            for(i=0, len=ring.components.length; i<len; ++i) {
                intersect = geometry.containsPoint(ring.components[i]);
                if(intersect) {
                    break;
                }
            }
        }
        return intersect;
    },

    /**
     * APIMethod: distanceTo
     * Calculate the closest distance between two geometries (on the x-y plane).
     *
     * Parameters:
     * geometry - {<OpenLayers.Geometry>} The target geometry.
     * options - {Object} Optional properties for configuring the distance
     *     calculation.
     *
     * Valid options:
     * details - {Boolean} Return details from the distance calculation.
     *     Default is false.
     * edge - {Boolean} Calculate the distance from this geometry to the
     *     nearest edge of the target geometry.  Default is true.  If true,
     *     calling distanceTo from a geometry that is wholly contained within
     *     the target will result in a non-zero distance.  If false, whenever
     *     geometries intersect, calling distanceTo will return 0.  If false,
     *     details cannot be returned.
     *
     * Returns:
     * {Number | Object} The distance between this geometry and the target.
     *     If details is true, the return will be an object with distance,
     *     x0, y0, x1, and y1 properties.  The x0 and y0 properties represent
     *     the coordinates of the closest point on this geometry. The x1 and y1
     *     properties represent the coordinates of the closest point on the
     *     target geometry.
     */
    distanceTo: function(geometry, options) {
        var edge = !(options && options.edge === false);
        var result;
        // this is the case where we might not be looking for distance to edge
        if(!edge && this.intersects(geometry)) {
            result = 0;
        } else {
            result = OpenLayers.Geometry.Collection.prototype.distanceTo.apply(
                this, [geometry, options]
            );
        }
        return result;
    },

    CLASS_NAME: "OpenLayers.Geometry.Polygon"
});

/**
 * APIMethod: createRegularPolygon
 * Create a regular polygon around a radius. Useful for creating circles 
 * and the like.
 *
 * Parameters:
 * origin - {<OpenLayers.Geometry.Point>} center of polygon.
 * radius - {Float} distance to vertex, in map units.
 * sides - {Integer} Number of sides. 20 approximates a circle.
 * rotation - {Float} original angle of rotation, in degrees.
 */
OpenLayers.Geometry.Polygon.createRegularPolygon = function(origin, radius, sides, rotation) {  
    var angle = Math.PI * ((1/sides) - (1/2));
    if(rotation) {
        angle += (rotation / 180) * Math.PI;
    }
    var rotatedAngle, x, y;
    var points = [];
    for(var i=0; i<sides; ++i) {
        rotatedAngle = angle + (i * 2 * Math.PI / sides);
        x = origin.x + (radius * Math.cos(rotatedAngle));
        y = origin.y + (radius * Math.sin(rotatedAngle));
        points.push(new OpenLayers.Geometry.Point(x, y));
    }
    var ring = new OpenLayers.Geometry.LinearRing(points);
    return new OpenLayers.Geometry.Polygon([ring]);
};