之前被同事紧急问起,location出来的经纬度怎么自已算出来方位角和距离。如果是自已算的话,一般来说是前后两秒经纬度进行计算。我在android 系统源码也看到计算方式。在这里进行贴出来,记录一下。
1、location 类
这个是location类。有android api源码都能找到的。
2、关键代码
private static void computeDistanceAndBearing(double lat1, double lon1, double lat2, double lon2, float[] results) { // Based on http://www.ngs.noaa.gov/PUBS_LIB/inverse.pdf // using the "Inverse Formula" (section 4) int MAXITERS = 20; // Convert lat/long to radians lat1 *= Math.PI / 180.0; lat2 *= Math.PI / 180.0; lon1 *= Math.PI / 180.0; lon2 *= Math.PI / 180.0; double a = 6378137.0; // WGS84 major axis double b = 6356752.3142; // WGS84 semi-major axis double f = (a - b) / a; double aSqMinusBSqOverBSq = (a * a - b * b) / (b * b); double L = lon2 - lon1; double A = 0.0; double U1 = Math.atan((1.0 - f) * Math.tan(lat1)); double U2 = Math.atan((1.0 - f) * Math.tan(lat2)); double cosU1 = Math.cos(U1); double cosU2 = Math.cos(U2); double sinU1 = Math.sin(U1); double sinU2 = Math.sin(U2); double cosU1cosU2 = cosU1 * cosU2; double sinU1sinU2 = sinU1 * sinU2; double sigma = 0.0; double deltaSigma = 0.0; double cosSqAlpha = 0.0; double cos2SM = 0.0; double cosSigma = 0.0; double sinSigma = 0.0; double cosLambda = 0.0; double sinLambda = 0.0; double lambda = L; // initial guess for (int iter = 0; iter < MAXITERS; iter++) { double lambdaOrig = lambda; cosLambda = Math.cos(lambda); sinLambda = Math.sin(lambda); double t1 = cosU2 * sinLambda; double t2 = cosU1 * sinU2 - sinU1 * cosU2 * cosLambda; double sinSqSigma = t1 * t1 + t2 * t2; // (14) sinSigma = Math.sqrt(sinSqSigma); cosSigma = sinU1sinU2 + cosU1cosU2 * cosLambda; // (15) sigma = Math.atan2(sinSigma, cosSigma); // (16) double sinAlpha = (sinSigma == 0) ? 0.0 : cosU1cosU2 * sinLambda / sinSigma; // (17) cosSqAlpha = 1.0 - sinAlpha * sinAlpha; cos2SM = (cosSqAlpha == 0) ? 0.0 : cosSigma - 2.0 * sinU1sinU2 / cosSqAlpha; // (18) double uSquared = cosSqAlpha * aSqMinusBSqOverBSq; // defn A = 1 + (uSquared / 16384.0) * // (3) (4096.0 + uSquared * (-768 + uSquared * (320.0 - 175.0 * uSquared))); double B = (uSquared / 1024.0) * // (4) (256.0 + uSquared * (-128.0 + uSquared * (74.0 - 47.0 * uSquared))); double C = (f / 16.0) * cosSqAlpha * (4.0 + f * (4.0 - 3.0 * cosSqAlpha)); // (10) double cos2SMSq = cos2SM * cos2SM; deltaSigma = B * sinSigma * // (6) (cos2SM + (B / 4.0) * (cosSigma * (-1.0 + 2.0 * cos2SMSq) - (B / 6.0) * cos2SM * (-3.0 + 4.0 * sinSigma * sinSigma) * (-3.0 + 4.0 * cos2SMSq))); lambda = L + (1.0 - C) * f * sinAlpha * (sigma + C * sinSigma * (cos2SM + C * cosSigma * (-1.0 + 2.0 * cos2SM * cos2SM))); // (11) double delta = (lambda - lambdaOrig) / lambda; if (Math.abs(delta) < 1.0e-12) { break; } } float distance = (float) (b * A * (sigma - deltaSigma)); results[0] = distance; if (results.length > 1) { float initialBearing = (float) Math.atan2(cosU2 * sinLambda, cosU1 * sinU2 - sinU1 * cosU2 * cosLambda); initialBearing *= 180.0 / Math.PI; results[1] = initialBearing; if (results.length > 2) { float finalBearing = (float) Math.atan2(cosU1 * sinLambda, -sinU1 * cosU2 + cosU1 * sinU2 * cosLambda); finalBearing *= 180.0 / Math.PI; results[2] = finalBearing; } } }
传入两个经纬度值,这个就不用高程。不用做过多的解释了。
源码封装的调用方式
方位角(航向角)
/** * Returns the approximate initial bearing in degrees East of true * North when traveling along the shortest path between this * location and the given location. The shortest path is defined * using the WGS84 ellipsoid. Locations that are (nearly) * antipodal may produce meaningless results. * * @param dest the destination location * @return the initial bearing in degrees */ public float bearingTo(Location dest) { synchronized (mResults) { // See if we already have the result if (mLatitude != mLat1 || mLongitude != mLon1 || dest.mLatitude != mLat2 || dest.mLongitude != mLon2) { computeDistanceAndBearing(mLatitude, mLongitude, dest.mLatitude, dest.mLongitude, mResults); mLat1 = mLatitude; mLon1 = mLongitude; mLat2 = dest.mLatitude; mLon2 = dest.mLongitude; mDistance = mResults[0]; mInitialBearing = mResults[1]; } return mInitialBearing; } }
距离:
/** * Returns the approximate distance in meters between this * location and the given location. Distance is defined using * the WGS84 ellipsoid. * * @param dest the destination location * @return the approximate distance in meters */ public float distanceTo(Location dest) { // See if we already have the result synchronized (mResults) { if (mLatitude != mLat1 || mLongitude != mLon1 || dest.mLatitude != mLat2 || dest.mLongitude != mLon2) { computeDistanceAndBearing(mLatitude, mLongitude, dest.mLatitude, dest.mLongitude, mResults); mLat1 = mLatitude; mLon1 = mLongitude; mLat2 = dest.mLatitude; mLon2 = dest.mLongitude; mDistance = mResults[0]; mInitialBearing = mResults[1]; } return mDistance; } }
都是调用这个方法进行计算的computeDistanceAndBearing。
想多了解android location方面: