hirondelle.formula.function.builtin
Class Bearing

Object
  hirondelle.formula.function.builtin.Bearing

All Implemented Interfaces:

Function

public final class Bearing
extends Object
implements Function

bearing(φ1, λ1, φ2, λ2): the compass bearing from one place to another.

Constructor Summary

Bearing()

Method Summary

Decimal

calculate(Decimal... aArgs) The bearing is the direction one must travel from a specific starting point (point 1) to get to a specific destination (point 2).

Methods inherited from class Object

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

Constructor Detail

Bearing

public Bearing()

Method Detail

calculate

public Decimal calculate(Decimal... aArgs)

The bearing is the direction one must travel from a specific starting point (point 1) to get to a specific destination (point 2).

Returns degrees from true north, positive towards the east, in the range 0..360.

This method takes 4 parameters, in the following order:

• φ1 - the latitude of the starting point, in degrees
• λ1 - the longitude of the starting point, in degrees
• φ2 - the latitude of the destination point, in degrees
• λ2 - the longitude of the destination point, in degrees

Latitude is positive north of the equator, and negative south of the equator. Longitude is positive to the east of Greenwich meridian (Asia, for example), and negative to the west of the Greenwich meridian (America, for example).

The return value usually has a large number of decimal places. That precision is spurious and without physical significance, since the underlying implementation makes the approximation that the Earth is spherical.

The caller should round the result to a reasonable number of decimal places. (Some applications may even decide to round the result to an integer.)

For reference, the crux of the formula is:

atan2(sin(Δλ) * cos(φ2), cos(φ1) * sin(φ2) - sin(φ1) * cos(φ2) * cos(Δλ)

Specified by:

calculate in interface Function

Parameters:

aArgs - 0 or more arguments to the function.