它正在找到直线上最接近鼠标的点。另请注意，这是一个Google Maps API v2示例（但v3的原理是相同的）。
// Code to find the distance in metres between a lat/lng point and a polyline of lat/lng points// All in WGS84. Free for any use.//// Bill Chadwick 2007// updated to Google Maps API v3, Lawrence Ross 2014 // Construct a bdccGeo from its latitude and longitude in degrees function bdccGeo(lat, lon) { var theta = (lon * Math.PI / 180.0); var rlat = bdccGeoGeocentricLatitude(lat * Math.PI / 180.0); var c = Math.cos(rlat); this.x = c * Math.cos(theta); this.y = c * Math.sin(theta); this.z = Math.sin(rlat); } bdccGeo.prototype = new bdccGeo(); // internal helper functions ========================================= // Convert from geographic to geocentric latitude (radians). function bdccGeoGeocentricLatitude(geographicLatitude) { var flattening = 1.0 / 298.257223563;//WGS84 var f = (1.0 - flattening) * (1.0 - flattening); return Math.atan((Math.tan(geographicLatitude) * f)); } // Returns the two antipodal points of intersection of two great // circles defined by the arcs geo1 to geo2 and // geo3 to geo4. Returns a point as a Geo, use .antipode to get the other point function bdccGeoGetIntersection( geo1, geo2, geo3, geo4) { var geoCross1 = geo1.crossNormalize(geo2); var geoCross2 = geo3.crossNormalize(geo4); return geoCross1.crossNormalize(geoCross2); } //from Radians to Meters function bdccGeoRadiansToMeters(rad) { return rad * 6378137.0; // WGS84 Equatorial Radius in Meters } //from Meters to Radians function bdccGeoMetersToRadians(m) { return m / 6378137.0; // WGS84 Equatorial Radius in Meters } // properties ================================================= bdccGeo.prototype.getLatitudeRadians = function() { return (bdccGeoGeographicLatitude(Math.atan2(this.z, Math.sqrt((this.x * this.x) + (this.y * this.y))))); } bdccGeo.prototype.getLongitudeRadians = function() { return (Math.atan2(this.y, this.x)); } bdccGeo.prototype.getLatitude = function() { return this.getLatitudeRadians() * 180.0 / Math.PI; } bdccGeo.prototype.getLongitude = function() { return this.getLongitudeRadians() * 180.0 / Math.PI ; } // Methods ================================================= //Maths bdccGeo.prototype.dot = function( b) { return ((this.x * b.x) + (this.y * b.y) + (this.z * b.z)); } //More Maths bdccGeo.prototype.crossLength = function( b) { var x = (this.y * b.z) - (this.z * b.y); var y = (this.z * b.x) - (this.x * b.z); var z = (this.x * b.y) - (this.y * b.x); return Math.sqrt((x * x) + (y * y) + (z * z)); } //More Maths bdccGeo.prototype.scale = function( s) { var r = new bdccGeo(0,0); r.x = this.x * s; r.y = this.y * s; r.z = this.z * s; return r; } // More Maths bdccGeo.prototype.crossNormalize = function( b) { var x = (this.y * b.z) - (this.z * b.y); var y = (this.z * b.x) - (this.x * b.z); var z = (this.x * b.y) - (this.y * b.x); var L = Math.sqrt((x * x) + (y * y) + (z * z)); var r = new bdccGeo(0,0); r.x = x / L; r.y = y / L; r.z = z / L; return r; } // point on opposite side of the world to this point bdccGeo.prototype.antipode = function() { return this.scale(-1.0); } //distance in radians from this point to point v2 bdccGeo.prototype.distance = function( v2) { return Math.atan2(v2.crossLength(this), v2.dot(this)); } //returns in meters the minimum of the perpendicular distance of this point from the line segment geo1-geo2 //and the distance from this point to the line segment ends in geo1 and geo2 bdccGeo.prototype.distanceToLineSegMtrs = function(geo1, geo2) { //point on unit sphere above origin and normal to plane of geo1,geo2 //could be either side of the plane var p2 = geo1.crossNormalize(geo2); // intersection of GC normal to geo1/geo2 passing through p with GC geo1/geo2 var ip = bdccGeoGetIntersection(geo1,geo2,this,p2); //need to check that ip or its antipode is between p1 and p2 var d = geo1.distance(geo2); var d1p = geo1.distance(ip); var d2p = geo2.distance(ip); //window.status = d + ", " + d1p + ", " + d2p; if ((d >= d1p) && (d >= d2p)) return bdccGeoRadiansToMeters(this.distance(ip)); else { ip = ip.antipode(); d1p = geo1.distance(ip); d2p = geo2.distance(ip); } if ((d >= d1p) && (d >= d2p)) return bdccGeoRadiansToMeters(this.distance(ip)); else return bdccGeoRadiansToMeters(Math.min(geo1.distance(this),geo2.distance(this))); } // distance in meters from GLatLng point to GPolyline or GPolygon poly function bdccGeoDistanceToPolyMtrs(poly, point) { var d = 999999999; var i; var p = new bdccGeo(point.lat(),point.lng()); for(i=0; i<(poly.getPath().getLength()-1); i++) { var p1 = poly.getPath().getAt(i); var l1 = new bdccGeo(p1.lat(),p1.lng()); var p2 = poly.getPath().getAt(i+1); var l2 = new bdccGeo(p2.lat(),p2.lng()); var dp = p.distanceToLineSegMtrs(l1,l2); if(dp < d) d = dp; } return d; } // get a new GLatLng distanceMeters away on the compass bearing azimuthDegrees // from the GLatLng point - accurate to better than 200m in 140km (20m in 14km) in the UK function bdccGeoPointAtRangeAndBearing (point, distanceMeters, azimuthDegrees) { var latr = point.lat() * Math.PI / 180.0; var lonr = point.lng() * Math.PI / 180.0; var coslat = Math.cos(latr); var sinlat = Math.sin(latr); var az = azimuthDegrees* Math.PI / 180.0; var cosaz = Math.cos(az); var sinaz = Math.sin(az); var dr = distanceMeters / 6378137.0; // distance in radians using WGS84 Equatorial Radius var sind = Math.sin(dr); var cosd = Math.cos(dr); return new google.maps.LatLng(Math.asin((sinlat * cosd) + (coslat * sind * cosaz)) * 180.0 / Math.PI, (Math.atan2((sind * sinaz), (coslat * cosd) - (sinlat * sind * cosaz)) + lonr) * 180.0 / Math.PI); }
