/*
** Hapgood defines a transformation between GSE and HEE in his 1992
** paper (section 6), but this part isn't online.
**
** The gist of it is, we rotate 180 degrees about Z, and then translate
** along X.
**
** But we also need to add "R", a constant vector defined by
**
** R = [ Rsun, 0, 0 ]
**
** where
**
** r0 (1 - e^2)
** Rsun = ------------
** 1 + e cos(v)
**
** r0 = 1.495985E8 km mean distance of the Sun from Earth.
**
** e = 0.016709 - 0.0000418T0 eccentricity of the Sun's apparent
** orbit around the Earth.
**
** w = 282.94 + 1.72 T0 longitude of perigee of that orbit
**
** v = lambda0 - w (see lambda0 above)
**
**
** Implemented by Ed Santiago, Updated by Kristi Keller
*/
int
gse_twixt_hee(const double et, Vec v_in, Vec v_out, Direction direction)
{
Mat mat;
double r0,e, w,v, Rsun;
hapgood_matrix(180, Z, mat);
/*
** Note that there's no transposition here if the direction is "back";
** the operation works identically in both directions.
*/
mat_times_vec(mat, v_in, v_out);
/* Translate the X axis about the earth-sun distance */
r0 = (double)1.495985e8;
e = 0.016709 - 0.0000418*T0(et);
w = 282.94 + 1.72*T0(et);
v = lambda0(et) - w;
Rsun = r0*(1-e*e)/(1.+e*cosd(v));
/* v_out[0] += (double)1.5e8; */
v_out[0] += Rsun;
return 0;
}
/*
** The GSE to GSEQ transformation is given by the matrix
**
** T6 = <theta, X>
**
** where theta is the angle between the Y-axes in the two systems. A full
** description can be found at
** http://www-ssc.igpp.ucla.edu/personnel/russell/papers/gct1.html/#s3.5
** (Geophysical Coordinate Transformations, C. T. Russell 1971)
*/
void
mat_T6(const double et, Mat mat)
{
Vec GSE_ES, GEI_ES, thetaD;
double theta, thetaN, magThetaD;
Mat matT2;
/* Get Earth-Sun vector in GEI */
GSE_ES[0] = 1.0;
GSE_ES[1] = 0.0;
GSE_ES[2] = 0.0;
/* Convert GSE --> GEI */
mat_T2(et, matT2);
mat_transpose(matT2, matT2);
mat_times_vec(matT2, GSE_ES, GEI_ES);
/* Rotation axis of the Sun (GEI): (1.217,- 0.424, 0.897) */
thetaN = GEI_ES[0]*(-0.032) + GEI_ES[1]*(-0.112) + GEI_ES[2]*(-0.048);
thetaD[0] = (-0.424)*GEI_ES[2] - 0.897*GEI_ES[1];
thetaD[1] = 0.897*GEI_ES[0] - 0.1217*GEI_ES[2];
thetaD[2] = 0.1217*GEI_ES[1] - (-0.424)*GEI_ES[0];
magThetaD = sqrt(pow(thetaD[0],2) + pow(thetaD[1], 2) + pow(thetaD[2], 2));
theta = asin(thetaN/magThetaD);
/* printf("Theta: %f\n", theta); */
hapgood_matrix((theta*RADIANS_TO_DEGREES), X, mat);
/* TODO: Unknown why transpose is necessary to match previous results */
mat_transpose(mat,mat);
}
/*
** vec_Qe
**
** don't ask.
*/
void
vec_Qe(double et, Vec Qe)
{
double lat = mag_lat(et);
double lon = mag_lon(et);
double cos_lat = cos(lat);
double sin_lat = sin(lat);
double cos_lon = cos(lon);
double sin_lon = sin(lon);
Mat mat_tmp, mat;
Vec Qg;
Qg[0] = cos_lat * cos_lon;
Qg[1] = cos_lat * sin_lon;
Qg[2] = sin_lat;
/* printf("lat=%lf lon=%lf\n", 90.0 - lat, lon);*/
mat_T2(et, mat);
mat_T1(et, mat_tmp);
mat_transpose(mat_tmp, mat_tmp);
mat_times_mat(mat, mat_tmp, mat);
mat_times_vec(mat, Qg, Qe);
}
Vec* rotate_vec_x(Vec* v, double theta) {
Mat* rotate_mat = create_mat(1, 0, 0, 0,
0, cos(theta), sin(theta), 0,
0, -sin(theta), cos(theta), 0,
0, 0, 0, 0);
Vec* r = mat_times_vec(rotate_mat, v);
delete_mat(rotate_mat);
return r;
}
Vec* rotate_vec(Vec* v, Vec* u, double theta) {
double c = cos(theta);
double s = sin(theta);
double x1 = c + u->x * u->x * (1 - c);
double x2 = u->x * u->y * (1 - c) - u->z * s;
double x3 = u->x * u->z * (1 - c) + u->y * s;
double y1 = u->y * u->x * (1 - c) + u->z * s;
double y2 = c + u->y * u->y * (1 - c);
double y3 = u->y * u->z * (1 - c) - u->x * s;
double z1 = u->z * u->x * (1 - c) - u->y * s;
double z2 = u->z * u->y * (1 - c) + u->x * s;
double z3 = c + u->z * u->z * (1 - c);
Mat* rotate_mat = create_mat(x1, y1, z1, 0,
x2, y2, z2, 0,
x3, y3, z3, 0,
0, 0, 0, 0);
Vec* r = mat_times_vec(rotate_mat, v);
delete_mat(rotate_mat);
return r;
}
/*********************\
** simple_rotation ** utility function used by all the "twixt" functions
**********************
**
** This is basically what all the "twixt" functions do:
**
** 1) define a rotation matrix
** 2) If doing an inverse transformation, transpose that matrix.
** 3) multiply the rotation matrix by the input vector.
**
** To save all that work in the "twixt" functions, they just call this
** function, passing us a pointer to a function that defines the matrix.
*/
int
simple_rotation(const double et, Vec v_in, Vec v_out, Direction d, void (*m)())
{
Mat mat;
/*
** Call the user-specified function to get a rotation matrix.
*/
(m)(et, mat);
/*
** To do the inverse transformation, we use the transposition of the matrix
*/
if (d == BACK)
mat_transpose(mat, mat);
/*
** Multiply the rotation matrix by the input vector, and that's it!
*/
mat_times_vec(mat, v_in, v_out);
return 0;
}
