hpe.m

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%                                 hpe.m
%  Scope:   This MATLAB macro computes the horizontal position error (range) 
%           when latitude and longitude for two points are given; WGS-84 
            constants are used.
%  Usage:   x = hpe(lat1,lon1,lat2,lon2)
%  Description of parameters:
%           lat1   - input, latitude of the first position point, in radians
%           lon1   - input, longitude of the first position point, in radians
%           lat2   - input, latitude of the second position point, in radians
%           lon2   - input, longitude of the second position point, in radians
%           xout   - output, horizontal position error (range) between the two 
%                    defined position points, in meters
%  Remarks: 1) The macro wgs84con should be called before using the macro hpe
%              in order to initialize the global variables used.
%           2) The computation accuracy is limited due to algorithm approxima-
%              tions; it is recommended to be used when the range is less than 
%              100 km.
%  External Matlab macros used: wgs84con
%  Last update:  01/07/01
%  Copyright (C) 1996-00 by LL Consulting. All Rights Reserved.

function  xout = hpe(lat1,lon1,lat2,lon2)

global   a_smaxis  eccentr2    %  see  macro  wgs84.con

dlat = lat1 - lat2;
dlon = lon1 - lon2;
temp1 = sin(0.5*(lat1 + lat2));
temp1 = 0.5*eccentr2*temp1*temp1;
deltaN = dlat*a_smaxis*(1. - eccentr2)*(1. + 3.*temp1);
deltaE = dlon*a_smaxis*cos(lat1)*(1. + temp1);
xout = sqrt(deltaN*deltaN + deltaE*deltaE);