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ELL_LL2RB

ELL_LL2RB

## Purpose

For two points on an ellipsoid return range and bearing.

## Calling Sequence

ell_ll2rb, lon1, lat1, lon2, lat2, dist, azi1, azi2

## Inputs

lon1, lat1 = Point 1 geodetic long and lat (deg). in
lon2, lat2 = Point 2 geodetic long and lat (deg). in

## Outputs

dist = Distance along surface of ellipsoid (m). out
azi1 = forward geodetic azimuth (pt1 to pt2, deg). out
azi1 = reverse geodetic azimuth (pt2 to pt1, deg). out
If point 2 eq point 1 then azi1, azi2 both returned as 0.

## Notes

Notes: Use ellipsoid,set=name to set working ellipsoid. Uses
T. Vincenty's method. Converted to IDL from FORTRAN code at
ftp://www.ngs.noaa.gov/pub/pcsoft/for_inv.3d/source/inverse.for

## Example

lon1 = 144.42486788D0 & lat1 = -37.95103341D0
lon2 = 143.92649552D0 & lat2 = -37.65282113D0
ell_ll2rb, lon1, lat1, lon2, lat2, dist, azi1, azi2
help, dist, azi1, azi2
Computed:
dist = 54972.271 meters
azi1 = 306.86816 deg
azi2 = 127.17363 deg

Reference: Direct and Inverse Solutions of Geodesics on the
Ellipsoid with Applications of Nested Equations.
T. Vincenty, Survey Review XXII, 176, April 1975. p 88-93.

The Vicenty formulae should be good over distances from a few
cm to nearly 20,000 km with millimeter accuracy.
ell_rb2ll is inverse.
ll2rb is spherical version.

## Modification History

R. Sterner, 2001 Sep 04
R. Sterner, 2002 May 01 --- Generalized ellipsoid.
R. Sterner, 2006 Jan 10 --- Fixed minor error noted by Bob Jensen.
R. Sterner, 2006 Feb 07 --- Added to help text to avoid 0 distance.
R. Sterner, 2006 Mar 19 --- Added reference to help text.
R. Sterner, 2010 May 04 --- Converted arrays from () to [].
R. Sterner, 2011 Apr 26 --- Handled point 2 EQ point 1 (finally).
R. Sterner, 2011 Apr 26 --- Cleaned up the code some.
R. Sterner, 2014 Jun 10 --- Added fix by Rick Chapman to avoid a hang.
Copyright (C) 2001, Johns Hopkins University/Applied Physics Laboratory
This software may be used, copied, or redistributed as long as it is not
sold and this copyright notice is reproduced on each copy made. This
routine is provided as is without any express or implied warranties
whatsoever. Other limitations apply as described in the file disclaimer.txt.

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