function [XF,YF,ZF,XX,YY,ZZ,M] = GEOPACK_EXAMPLE2
%function [XF,YF,ZF,XX,YY,ZZ,M] = GEOPACK_EXAMPLE2;
%       PROGRAM EXAMPLE2
% XF,YF,ZF end of example field line trace (GSM)
% XX,YY,ZZ all points in field line trace (GSM)
% M index of last 'real' point in field line trace
% C
% C  THIS IS ANOTHER EXAMPLE OF USING THE GEOPACK SUBROUTINE "TRACE". UNLIKE IN THE EXAMPLE1,
% C  HERE WE ASSUME A PURELY DIPOLAR APPROXIMATION FOR THE EARTH'S INTERNAL FIELD.
% C  IN THIS CASE WE ALSO EXPLICITLY SPECIFY THE TILT ANGLE OF THE GEODIPOLE,
% C  INSTEAD OF CALCULATING IT FROM THE DATE/TIME.
% 
% C
% C  Unlike in the EXAMPLE1, here we "manually" specify the tilt angle and its sine/cosine.
% c  To forward them to the coordinate transformation subroutines, we need to explicitly
% c  include the common block /GEOPACK1/:
% 
% C

%%%  original GEOPACK1 from RECALC
% % %       COMMON /GEOPACK1/ ST0,CT0,SL0,CL0,CTCL,STCL,CTSL,STSL,SFI,CFI,SPS,
% % %      * CPS,SHI,CHI,HI,PSI,XMUT,A11,A21,A31,A12,A22,A32,A13,A23,A33,DS3,
% % %      * CGST,SGST,BA(6)
%      COMMON /GEOPACK1/ AA(10),SPS,CPS,BB(3),PS,CC(19)
global GEOPACK1;
% PS -> GEOPACK1.PSI

%       DIMENSION XX(500),YY(500),ZZ(500), PARMOD(10)
% c
% c be sure to include an EXTERNAL statement with the names of (i) a magnetospheric
% c external field model and (ii) Earth's internal field model.
% c
%       EXTERNAL T96_01, DIP
% C
% C   First, call RECALC, to define the main field coefficients and, hence, the magnetic
% C      moment of the geodipole for IYEAR=1997 and IDAY=350.
% C   The universal time does not matter in this example, because here we explicitly
% C   specify the tilt angle (hence, the orientation of the dipole in the GSM coordinates),
% C   and we arbitrarily set IHOUR=MIN=ISEC=0  (any other values would be OK):
% c

GEOPACK_RECALC (1997,350,0,0,0);
% c
% c   Enter T96 model input parameters:
% c
%       PRINT *, '   ENTER SOLAR WIND RAM PRESSURE IN NANOPASCALS'
%       READ *, PARMOD(1)
PARMOD(1) = 3; % Solar Wind Ram Pressure, nPa

% % C
%       PRINT *, '   ENTER DST '
%       READ *, PARMOD(2)
PARMOD(2) = -20; % Dst, nT

% % C
%       PRINT *, '   ENTER IMF BY AND BZ'
%       READ *, PARMOD(3),PARMOD(4)
PARMOD(3) = 3; % By, GSM, nT
PARMOD(4) = -3; % Bz, GSM, nT


% c  Define the latitude (XLAT) and longitude (XLON) of the field line footpoint
% c   in the GSM coordinate system:
% c
XLAT=75.;
XLON=180.;
% C
% C  Specify the dipole tilt angle PS, its sine SPS and cosine CPS, entering
% c    in the common block /GEOPACK1/:
% C
GEOPACK1.PSI=0.;
GEOPACK1.SPS=sin(GEOPACK1.PSI);
GEOPACK1.CPS=cos(GEOPACK1.PSI);
% c
% c   Calculate Cartesian coordinates of the starting footpoint:
% c
T=(90.-XLAT)*.01745329;
XL=XLON*.01745329;
XGSM=sin(T)*cos(XL);
YGSM=sin(T)*sin(XL);
ZGSM=cos(T);
% C
% c   SPECIFY TRACING PARAMETERS:
% C
DIR=1.;
% C            (TRACE THE LINE WITH A FOOTPOINT IN THE NORTHERN HEMISPHERE, THAT IS,
% C             ANTIPARALLEL TO THE MAGNETIC FIELD)

RLIM=60.;
% C            (LIMIT THE TRACING REGION WITHIN R=60 Re)
% C
R0=1.;
% C            (LANDING POINT WILL BE CALCULATED ON THE SPHERE R=1,
% C                   I.E. ON THE EARTH'S SURFACE)
% c
IOPT=0;
% C           (IN THIS EXAMPLE IOPT IS JUST A DUMMY PARAMETER,
% C                 WHOSE VALUE DOES NOT MATTER)
% c
% c  Trace the field line:
% c
[XF,YF,ZF,XX,YY,ZZ,M] = GEOPACK_TRACE (XGSM,YGSM,ZGSM,DIR,RLIM,R0,IOPT,PARMOD,'T96','GEOPACK_DIP');
% C
% C   Write the result in the output file 'LINTEST2.DAT':
% C
%        OPEN(UNIT=1, FILE='LINTEST2.DAT',STATUS='NEW')
%   1   WRITE (1,20) (XX(L),YY(L),ZZ(L),L=1,M)
%  20   FORMAT((2X,3F6.2))
% 
%       CLOSE(UNIT=1)
%       STOP
%       END
% end of function EXAMPLE2

%%%%%%%%%%% END OF EXAMPLES