/**
* Computes distance (in km), azimuth (degrees clockwise positive from North, 0 to 360), and back
* azimuth (degrees clockwise positive from North, 0 to 360), from latitude-longituide point pt1
* to latitude-longituide pt2.
*
* <p>Algorithm from U.S. National Geodetic Survey, FORTRAN program "inverse," subroutine
* "INVER1," by L. PFEIFER and JOHN G. GERGEN. See
* http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html
*
* <p>Original documentation: <br>
* SOLUTION OF THE GEODETIC INVERSE PROBLEM AFTER T.VINCENTY <br>
* MODIFIED RAINSFORD'S METHOD WITH HELMERT'S ELLIPTICAL TERMS <br>
* EFFECTIVE IN ANY AZIMUTH AND AT ANY DISTANCE SHORT OF ANTIPODAL <br>
* STANDPOINT/FOREPOINT MUST NOT BE THE GEOGRAPHIC POLE Reference ellipsoid is the WGS-84
* ellipsoid. <br>
* See http://www.colorado.edu/geography/gcraft/notes/datum/elist.html
*
* <p>Requires close to 1.4 E-5 seconds wall clock time per call on a 550 MHz Pentium with Linux
* 7.2.
*
* @param e Earth object (defines radius and flattening)
* @param lat1 Lat of point 1
* @param lon1 Lon of point 1
* @param lat2 Lat of point 2
* @param lon2 Lon of point 2
* @param result put result here, or null to allocate
* @return a Bearing object with distance (in km), azimuth from pt1 to pt2 (degrees, 0 = north,
* clockwise positive)
*/
public static Bearing calculateBearing(
Earth e, double lat1, double lon1, double lat2, double lon2, Bearing result) {
if (result == null) {
result = new Bearing();
}
if ((lat1 == lat2) && (lon1 == lon2)) {
result.distance = 0;
result.azimuth = 0;
result.backazimuth = 0;
return result;
}
A = e.getMajor();
F = e.getFlattening();
R = 1.0 - F;
// Algorithm from National Geodetic Survey, FORTRAN program "inverse,"
// subroutine "INVER1," by L. PFEIFER and JOHN G. GERGEN.
// http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html
// Conversion to JAVA from FORTRAN was made with as few changes as possible
// to avoid errors made while recasting form, and to facilitate any future
// comparisons between the original code and the altered version in Java.
// Original documentation:
// SOLUTION OF THE GEODETIC INVERSE PROBLEM AFTER T.VINCENTY
// MODIFIED RAINSFORD'S METHOD WITH HELMERT'S ELLIPTICAL TERMS
// EFFECTIVE IN ANY AZIMUTH AND AT ANY DISTANCE SHORT OF ANTIPODAL
// STANDPOINT/FOREPOINT MUST NOT BE THE GEOGRAPHIC POLE
// A IS THE SEMI-MAJOR AXIS OF THE REFERENCE ELLIPSOID
// F IS THE FLATTENING (NOT RECIPROCAL) OF THE REFERNECE ELLIPSOID
// LATITUDES GLAT1 AND GLAT2
// AND LONGITUDES GLON1 AND GLON2 ARE IN RADIANS POSITIVE NORTH AND EAST
// FORWARD AZIMUTHS AT BOTH POINTS RETURNED IN RADIANS FROM NORTH
//
// Reference ellipsoid is the WGS-84 ellipsoid.
// See http://www.colorado.edu/geography/gcraft/notes/datum/elist.html
// FAZ is forward azimuth in radians from pt1 to pt2;
// BAZ is backward azimuth from point 2 to 1;
// S is distance in meters.
//
// Conversion to JAVA from FORTRAN was made with as few changes as possible
// to avoid errors made while recasting form, and to facilitate any future
// comparisons between the original code and the altered version in Java.
//
// IMPLICIT REAL*8 (A-H,O-Z)
// COMMON/CONST/PI,RAD
// COMMON/ELIPSOID/A,F
double GLAT1 = rad * lat1;
double GLAT2 = rad * lat2;
double TU1 = R * Math.sin(GLAT1) / Math.cos(GLAT1);
double TU2 = R * Math.sin(GLAT2) / Math.cos(GLAT2);
double CU1 = 1. / Math.sqrt(TU1 * TU1 + 1.);
double SU1 = CU1 * TU1;
double CU2 = 1. / Math.sqrt(TU2 * TU2 + 1.);
double S = CU1 * CU2;
double BAZ = S * TU2;
double FAZ = BAZ * TU1;
double GLON1 = rad * lon1;
double GLON2 = rad * lon2;
double X = GLON2 - GLON1;
double D, SX, CX, SY, CY, Y, SA, C2A, CZ, E, C;
int loopCnt = 0;
do {
loopCnt++;
// Check for an infinite loop
if (loopCnt > 1000) {
throw new IllegalArgumentException(
"Too many iterations calculating bearing:"
+ lat1
+ " "
+ lon1
+ " "
+ lat2
+ " "
+ lon2);
}
SX = Math.sin(X);
CX = Math.cos(X);
TU1 = CU2 * SX;
TU2 = BAZ - SU1 * CU2 * CX;
SY = Math.sqrt(TU1 * TU1 + TU2 * TU2);
CY = S * CX + FAZ;
Y = Math.atan2(SY, CY);
SA = S * SX / SY;
C2A = -SA * SA + 1.;
CZ = FAZ + FAZ;
if (C2A > 0.) {
CZ = -CZ / C2A + CY;
}
E = CZ * CZ * 2. - 1.;
C = ((-3. * C2A + 4.) * F + 4.) * C2A * F / 16.;
D = X;
X = ((E * CY * C + CZ) * SY * C + Y) * SA;
X = (1. - C) * X * F + GLON2 - GLON1;
// IF(DABS(D-X).GT.EPS) GO TO 100
} while (Math.abs(D - X) > EPS);
if (loopCnt > maxLoopCnt) {
maxLoopCnt = loopCnt;
// System.err.println("loopCnt:" + loopCnt);
}
FAZ = Math.atan2(TU1, TU2);
BAZ = Math.atan2(CU1 * SX, BAZ * CX - SU1 * CU2) + Math.PI;
X = Math.sqrt((1. / R / R - 1.) * C2A + 1.) + 1.;
X = (X - 2.) / X;
C = 1. - X;
C = (X * X / 4. + 1.) / C;
D = (0.375 * X * X - 1.) * X;
X = E * CY;
S = 1. - E - E;
S = ((((SY * SY * 4. - 3.) * S * CZ * D / 6. - X) * D / 4. + CZ) * SY * D + Y) * C * A * R;
result.distance = S / 1000.0; // meters to km
result.azimuth = FAZ * deg; // radians to degrees
if (result.azimuth < 0.0) {
result.azimuth += 360.0; // reset azs from -180 to 180 to 0 to 360
}
result.backazimuth = BAZ * deg; // radians to degrees; already in 0 to 360 range
return result;
}
