地心惯性坐标系转大地坐标系 java代码

地心惯性坐标系（Earth-Centered Inertial，ECI）是以地球为中心的惯性坐标系。而大地坐标系（Geodetic Coordinates）是以地球表面的形状和大小为基础的坐标系。下面是 Java 代码实现 ECI 坐标系到大地坐标系的转换：

import org.apache.commons.math3.geometry.euclidean.threed.Vector3D;
import org.apache.commons.math3.util.FastMath;

public class EciToGeodetic {

    private final double WGS84_A = 6378137.0; // semi-major axis of the Earth
    private final double WGS84_B = 6356752.314245; // semi-minor axis of the Earth
    private final double WGS84_F = 1.0 / 298.257223563; // Earth flattening coefficient

    public GeodeticCoordinate convertEciToGeodetic(Vector3D positionEci, double gmst) {

        double x = positionEci.getX();
        double y = positionEci.getY();
        double z = positionEci.getZ();

        double r = FastMath.sqrt(x * x + y * y + z * z);
        double f = (WGS84_A - WGS84_B) / WGS84_A;
        double e2 = 1.0 - (WGS84_B * WGS84_B) / (WGS84_A * WGS84_A);
        double r0 = WGS84_A / FastMath.sqrt(1.0 - e2 * FastMath.sin(gmst) * FastMath.sin(gmst));
        double u = FastMath.atan(z / FastMath.sqrt(x * x + y * y));
        double l = FastMath.atan(y / x);

        double lat;
        double lon;
        double alt;

        do {
            lat = u;
            double sinLat = FastMath.sin(lat);
            double cosLat = FastMath.cos(lat);
            double cosLatSq = cosLat * cosLat;
            double nu = WGS84_A / FastMath.sqrt(1.0 - e2 * sinLat * sinLat);
            double p = r * cosLat - nu * cosLatSq;
            double zPrime = r * sinLat + e2 * nu * sinLat;
            alt = FastMath.sqrt(p * p + zPrime * zPrime) - nu;
            u = FastMath.atan((zPrime / p) * (1.0 - f * nu / (nu + alt)));
        } while (FastMath.abs(u - lat) > 1e-12);

        lat *= 180.0 / FastMath.PI;
        lon = l - gmst;
        lon *= 180.0 / FastMath.PI;
        if (lon < -180.0) {
            lon += 360.0;
        } else if (lon > 180.0) {
            lon -= 360.0;
        }

        return new GeodeticCoordinate(lat, lon, alt);
    }

    public static class GeodeticCoordinate {

        private final double latitude;
        private final double longitude;
        private final double altitude;

        public GeodeticCoordinate(double latitude, double longitude, double altitude) {
            this.latitude = latitude;
            this.longitude = longitude;
            this.altitude = altitude;
        }

        public double getLatitude() {
            return latitude;
        }

        public double getLongitude() {
            return longitude;
        }

        public double getAltitude() {
            return altitude;
        }
    }
}

其中，`positionEci` 是在 ECI 坐标系下的位置向量，`gmst` 是格林威治平恒星时。调用 `convertEciToGeodetic` 方法可以将 ECI 坐标系下的位置向量转换为大地坐标系下的经纬度和海拔高度。