function [east, north] = lonlat2km(lon_orig,lat_orig,lon,lat)
%LONLAT2KM  Convert lat/lon to distances (km) referenced to a lon/lat point.
%
%   This function will convert longitude/latitude pairs to distances in 
%   kilometers east and west of a reference longitude/latitude point.  The
%   equation used is from Bowditch's book "The American Practical Navigator."
%
% Usage:
%   [EAST,NORTH]=LONLAT2KM(LON_ORIG,LAT_ORIG,LON,LAT)
%
%
% Inputs:  lon_orig - reference longitude.
%	   lat_orig - reference latitude.
%	   lon      - longitude scalar or vector.
%	   lat      - latitude scalar or vector.
%
% Outputs: east     - distance east from reference point (km)
%          north    - distance north from reference point (km)
%
% Example: 
%	   	[EAST,NORTH]=LONLAT2KM(-122,35.4,LON,LAT)
%          will convert the vectors LON and LAT, which contain lon/lat pairs, 
%	   to distances in km east and north of -122 W, 35.4 N, returned
%          in the vectors EAST and NORTH. 

%	Mike Cook - NPS Oceanography Dept. - FEB 94
%       Mike Cook - JUN 94 - added more documentation and error checking.


	if nargin ~= 4
	   error(' You *MUST* supply 4 input arguments ')
	end
	
	
	con = radians(lat_orig);
	ymetr = 111132.09 - 566.05 .* cos(2 .* con) + 1.2 ...
                .* cos(4 .* con) - 0.002 .* cos(6 .* con);
	xmetr = 111415.13 .* cos(con) - 94.55 .* cos(3 .* con) ...
                + 0.012 .* cos(5 .* con);
        east = (lon - lon_orig) .* xmetr ./ 1000;
        north = (lat - lat_orig) .* ymetr ./ 1000;