com.bbn.openmap.proj
Class GreatCircle

java.lang.Object
  |
  +--com.bbn.openmap.proj.GreatCircle

public class GreatCircle

extends java.lang.Object

Methods for calculating great circle and other distances on the sphere and ellipsoid.

Spherical equations taken from John Synder's Map Projections --A Working Manual , pp29-31.
Latitude/longitude arguments must be in valid radians: -PI<=lambda<PI, -PI/2<=phi<=PI/2

Method Summary

static float[]	earth_circle(float phi1, float lambda0, float c, float s, float e, int n) Calculate partial earth circle on the sphere.
static float[]	earth_circle(float phi1, float lambda0, float c, float s, float e, int n, float[] ret_val) Calculate earth circle in the sphere.
static float[]	earth_circle(float phi1, float lambda0, float c, int n) Calculate earth circle on the sphere.
static float[]	earth_circle(float phi1, float lambda0, float c, int n, float[] ret_val) Calculate earth circle in the sphere.
static AziDist	ellipsoidalAziDist(double a, double finv, double glat1, double glon1, double glat2, double glon2, AziDist ret_val) Deprecated. this has been yanked until we have a more stable and documented algorithm
static float[]	great_circle(float phi1, float lambda0, float phi, float lambda, int n, boolean include_last) Calculate great circle between two points on the sphere.
static float	spherical_azimuth(float phi1, float lambda0, float phi, float lambda) Calculate spherical azimuth between two points.
static LatLonPoint	spherical_between(float phi1, float lambda0, float c, float Az) Calculate point at azimuth and distance from another point.
static float[]	spherical_between(float phi1, float lambda0, float c, float Az, int n) Calculate point between two points.
static float	spherical_distance(float phi1, float lambda0, float phi, float lambda) Calculate spherical arc distance between two points.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

ellipsoidalAziDist

public static final AziDist ellipsoidalAziDist(double a,
                                               double finv,
                                               double glat1,
                                               double glon1,
                                               double glat2,
                                               double glon2,
                                               AziDist ret_val)

Deprecated. this has been yanked until we have a more stable and documented algorithm

Determine azimuth and distance on the ellipsoid.

Parameters:

a - Semi-major axis of ellipsoid

finv - flattening of the ellipsoid (WGS84 is 1/298.257)

glat1 - Latitude of from station

glon1 - Longitude of from station

glat2 - Latitude of to station

glon2 - Longitude of to station

ret_val - AziDist struct

Returns:

AziDist ret_val struct with azimuth and distance

spherical_distance

public static final float spherical_distance(float phi1,
                                             float lambda0,
                                             float phi,
                                             float lambda)

Calculate spherical arc distance between two points.

Computes arc distance `c' on the sphere. equation (5-3a). (0 <= c <= PI)

Parameters:

phi1 - latitude in radians of start point

lambda0 - longitude in radians of start point

phi - latitude in radians of end point

lambda - longitude in radians of end point

Returns:

float arc distance `c'

spherical_azimuth

public static final float spherical_azimuth(float phi1,
                                            float lambda0,
                                            float phi,
                                            float lambda)

Calculate spherical azimuth between two points.

Computes the azimuth `Az' east of north from phi1, lambda0 bearing toward phi and lambda. (5-4b). (-PI <= Az <= PI).

Parameters:

phi1 - latitude in radians of start point

lambda0 - longitude in radians of start point

phi - latitude in radians of end point

lambda - longitude in radians of end point

Returns:

float azimuth east of north `Az'

spherical_between

public static final LatLonPoint spherical_between(float phi1,
                                                  float lambda0,
                                                  float c,
                                                  float Az)

Calculate point at azimuth and distance from another point.

Returns a LatLonPoint at arc distance `c' in direction `Az' from start point.

Parameters:

phi1 - latitude in radians of start point

lambda0 - longitude in radians of start point

c - arc radius in radians (0 < c <= PI)

Az - azimuth (direction) east of north (-PI <= Az < PI)

Returns:

LatLonPoint

spherical_between

public static final float[] spherical_between(float phi1,
                                              float lambda0,
                                              float c,
                                              float Az,
                                              int n)

Calculate point between two points.

Same as spherical_between() above except it calculates n equal segments along the length of c.

Parameters:

phi1 - latitude in radians of start point

lambda0 - longitude in radians of start point

c - arc radius in radians (0 < c <= PI)

Az - azimuth (direction) east of north (-PI <= Az < PI)

n - number of points along great circle edge to calculate

Returns:

float[n+1] radian lat,lon pairs

great_circle

public static final float[] great_circle(float phi1,
                                         float lambda0,
                                         float phi,
                                         float lambda,
                                         int n,
                                         boolean include_last)

Calculate great circle between two points on the sphere.

Folds all computation (distance, azimuth, points between) into one function for optimization. returns n or n+1 pairs of lat,lon on great circle between lat-lon pairs.

Parameters:

phi1 - latitude in radians of start point

lambda0 - longitude in radians of start point

phi - latitude in radians of end point

lambda - longitude in radians of end point

n - number of segments

include_last - return n or n+1 segments

Returns:

float[n] or float[n+1] radian lat,lon pairs

earth_circle

public static final float[] earth_circle(float phi1,
                                         float lambda0,
                                         float c,
                                         float s,
                                         float e,
                                         int n)

Calculate partial earth circle on the sphere.

Returns n float lat,lon pairs at arc distance c from point at phi1,lambda0.

Parameters:

phi1 - latitude in radians of center point

lambda0 - longitude in radians of center point

c - arc radius in radians (0 < c < PI)

s - starting angle in radians. North up is zero.

e - angular extent in radians, clockwise right from starting angle.

n - number of points along circle edge to calculate

Returns:

float[n] radian lat,lon pairs along earth circle

earth_circle

public static final float[] earth_circle(float phi1,
                                         float lambda0,
                                         float c,
                                         int n)

Calculate earth circle on the sphere.

Returns n float lat,lon pairs at arc distance c from point at phi1,lambda0.

Parameters:

phi1 - latitude in radians of center point

lambda0 - longitude in radians of center point

c - arc radius in radians (0 < c < PI)

n - number of points along circle edge to calculate

Returns:

float[n] radian lat,lon pairs along earth circle

earth_circle

public static final float[] earth_circle(float phi1,
                                         float lambda0,
                                         float c,
                                         int n,
                                         float[] ret_val)

Calculate earth circle in the sphere.

Returns n float lat,lon pairs at arc distance c from point at phi1,lambda0.

Parameters:

phi1 - latitude in radians of center point

lambda0 - longitude in radians of center point

c - arc radius in radians (0 < c < PI)

n - number of points along circle edge to calculate

ret_val - float[] ret_val array of n*2 number of points along circle edge to calculate

Returns:

float[n] radian lat,lon pairs along earth circle

earth_circle

public static final float[] earth_circle(float phi1,
                                         float lambda0,
                                         float c,
                                         float s,
                                         float e,
                                         int n,
                                         float[] ret_val)

Calculate earth circle in the sphere.

Returns n float lat,lon pairs at arc distance c from point at phi1,lambda0.

Parameters:

phi1 - latitude in radians of center point.

lambda0 - longitude in radians of center point.

c - arc radius in radians (0 < c < PI).

s - starting angle in radians. North up is zero.

e - angular extent in radians, clockwise right from starting angle.

n - number of points along circle edge to calculate.

ret_val - float[] ret_val array of n*2 number of points along circle edge to calculate.

Returns:

float[n] radian lat,lon pairs along earth circle.