int main (int argc, char **argv) {
double lat, lon, time;
furnsh_c("/home/user/BCGIT/ASTRO/standard.tm");
for (int i=0; i< 100000; i++) {
lat = pi_c()*rand()/RAND_MAX-halfpi_c();
lon = twopi_c()*rand()/RAND_MAX-pi_c();
time = 1167721200.*rand()/RAND_MAX + 946684800.;
// failing badly, so testing w/ knownish values
// lat = 0.611738;
// lon = -1.85878;
// time = 1554616800.+i;
// double elev = bc_elev(lat, lon, unix2et(time), "10");
double elev = bc_elev(lat, lon, unix2et(time), "10");
printf("%f,%f,%f,%f\n", lat, lon, time, elev);
}
}
double bc_elev(double lat, double lon, double et, char *target) {
double pos[3], radii[3], normal[3], state[6], lt;
int n;
// the Earth's 3 radii
bodvrd_c ("EARTH", "RADII", 3, &n, radii);
double flat = (radii[2]-radii[0])/radii[0];
// rectangular coordinates of position (ITRF93)
georec_c (lon, lat, 0, radii[0], flat, pos);
// surface normal vector to ellipsoid at latitude/longitude (this is
// NOT the same as pos!)
surfnm_c(radii[0], radii[1], radii[2], pos, normal);
// printf("POS: %f %f %f\n", pos[0], pos[1], pos[2]);
// printf("NORMAL: %f %f %f\n", normal[0], normal[1], normal[2]);
// printf("ET = %f\n", et);
// printf("POS: %f %f %f\n", pos[0], pos[1], pos[2]);
// position of Sun in ITRF93
spkcpo_c("Sun", et, "ITRF93", "OBSERVER", "CN+S", pos, "Earth", "ITRF93", state, <);
// printf("STATE: %f %f %f\n", state[0], state[1], state[2]);
double el = halfpi_c() - vsep_c(state, normal);
// printf("DEBUG: %f,%f,%f,%f,%f\n", lat, lon, 0., el, et);
// return halfpi_c() - vsep_c(normal, state);
return el;
}
SpiceDouble vsepg_c ( ConstSpiceDouble * v1,
ConstSpiceDouble * v2,
SpiceInt ndim )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
v1 I First vector.
v2 I Second vector.
ndim I The number of elements in v1 and v2.
-Detailed_Input
v1 is any double precision vector of arbitrary dimension.
v2 is also a double precision vector of arbitrary dimension.
v1 or v2 or both may be the zero vector.
ndim is the dimension of the both of the input vectors
v1 and v2.
-Detailed_Output
vsepg_c the angle between v1 and v2 expressed in radians.
vsepg_c is strictly non-negative. For input vectors of
four or more dimensions, the angle is defined as the
generalization of the definition for three dimensions.
If either v1 or v2 is the zero vector, then vsepg_c is
defined to be 0 radians.
-Parameters
None.
-Particulars
In four or more dimensions this angle does not have a physically
realizable interpretation. However, the angle is defined as
the generalization of the following definition which is valid in
three or two dimensions:
In the plane, it is a simple matter to calculate the angle
between two vectors once the two vectors have been made to be
unit length. Then, since the two vectors form the two equal
sides of an isosceles triangle, the length of the third side
is given by the expression
length = 2.0 * sine ( vsepg/2.0 )
The length is given by the magnitude of the difference of the
two unit vectors
length = norm ( u1 - u2 )
Once the length is found, the value of vsepg_c may be calculated
by inverting the first expression given above as
vsepg_c = 2.0 * arcsine ( length/2.0 )
This expression becomes increasingly unstable when vsepg_c gets
larger than pi/2 or 90 degrees. In this situation (which is
easily detected by determining the sign of the dot product of
v1 and v2) the supplementary angle is calculated first and
then vsepg_c is given by
vsepg_c = pi - SUPPLEMENTARY_ANGLE
-Examples
The following table gives sample values for v1, v2 and vsepg_c
implied by the inputs.
v1 v2 ndim vsepg_c
-----------------------------------------------------------------
(1, 0, 0, 0) (1, 0, 0, 0) 4 0.0
(1, 0, 0) (0, 1, 0) 3 pi/2 (=1.71...)
(3, 0) (-5, 0) 2 pi (=3.14...)
-Restrictions
The user is required to insure that the input vectors will not
cause floating point overflow upon calculation of the vector
dot product since no error detection or correction code is
implemented. In practice, this is not a significant
restriction.
-Exceptions
Error free.
-Files
None
-Author_and_Institution
C.A. Curzon (JPL)
K.R. Gehringer (JPL)
H.A. Neilan (JPL)
W.L. Taber (JPL)
E.D. Wright (JPL)
-Literature_References
None
-Version
-CSPICE Version 1.0.0, 29-JUN-1999
-Index_Entries
angular separation of n-dimensional vectors
-&
*/
{ /* Begin vsepg_c */
/*
Local variables
*/
SpiceDouble mag1;
SpiceDouble mag2;
SpiceDouble mag_dif;
SpiceDouble r1;
SpiceDouble r2;
SpiceInt i;
mag1 = vnormg_c( v1, ndim);
mag2 = vnormg_c( v2, ndim);
/*
If either v1 or v2 have magnitude zero, the separation is 0.
*/
if ( ( mag1 == 0.) || ( mag2 == 0.) )
{
return 0;
}
if ( vdotg_c( v1, v2, ndim ) < 0. )
{
r1 = 1./mag1;
r2 = 1./mag2;
mag_dif = 0.;
for ( i = 0; i < ndim; i++ )
{
mag_dif += pow( ( v1[i]*r1 - v2[i]*r2 ), 2);
}
mag_dif = sqrt(mag_dif);
return ( 2. * asin (0.5 * mag_dif) );
}
else if ( vdotg_c (v1, v2, ndim) > 0. )
{
r1 = 1./mag1;
r2 = 1./mag2;
mag_dif = 0.;
for ( i = 0; i < ndim; i++ )
{
mag_dif += pow( ( v1[i]*r1 + v2[i]*r2 ), 2);
}
mag_dif = sqrt(mag_dif);
return ( pi_c() - 2. * asin (0.5 * mag_dif) );
}
return ( halfpi_c());
} /* End vsepg_c */
