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% loc2gg.m:  transforms the scattering point location given in local coordinates

% GUISDAP v.1.60 96-05-27 Copyright Asko Huuskonen and Markku Lehtinen

%

% loc   [elevation, azimuth, range] at location

% site1 [latitude, longitude, height]  to geographic coordinates

% Thanks to J. Murgin (KGI Reprot NO 80:2), EISCAT analysis package, and P.Pollari

%

% In bistatic case, where another reference site (site2) is given

% the routine returns the scattering angle and ranges.

%

% See also: gg2gc, gc2gg, radar_eq

%

%function [gg_sp,angle,ranges]=loc2gg(site1,loc,site2)

function [gg_sp,angle,ranges]=loc2gg(site1,loc,site2)



factor=pi/180;        % conversion factor from degrees to radians



% first calculate the  transformation matrices

lat1=site1(1)*factor;

lon1=site1(2)*factor;

sinlat=sin(lat1);

coslat=cos(lat1);

sinlon=sin(lon1);

coslon=cos(lon1);

rlocgc=  [ sinlat*coslon -sinlon coslat*coslon;

           sinlat*sinlon  coslon coslat*sinlon;

          -coslat            0      sinlat    ];



s1=loc(1)*factor;s2=loc(2)*factor;s3=loc(3);

loc=s3*[-cos(s2)*cos(s1);sin(s2)*cos(s1);sin(s1)];



gc_site1=gg2gc(site1);          % Site1 to geogentric

gc_sp=gc_site1+(rlocgc*loc)';   % Add scattering distance in geocentric

gg_sp=gc2gg(gc_sp);             % Transform back to geographic



if nargin==3 % bistatic case

  gc_site2=gg2gc(site2);     % Site2 to geogentric

  gc_site1=gc_site1-gc_sp;   % Move origin to scattering point

  gc_site2=gc_site2-gc_sp;   % And same for site2

  ranges=[sqrt(sum(gc_site1.^2)) sqrt(sum(gc_site2.^2))];

  angle=pi-acos(sum(gc_site1.*gc_site2)/ranges(1)/ranges(2));

end