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Verified JPL Horizon velocity angles.

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Calculated the angles between JPL Horizons velocity vectors
for the geocentric Moon and the geocentric L4/L5.
They are always very close to 60 degrees apart, within 0.15 arcsec.
This is not large enough to explain the velocity vector
errors my code calculates.
This commit is contained in:
Don Cross
2022-02-16 19:53:59 -05:00
parent 8ba15530ac
commit 6e142a1df5
1 changed files with 48 additions and 0 deletions
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48
generate/ctest.c
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@@ -5182,6 +5182,54 @@ static int LagrangeJplAnalyzeFiles(
printf(" length ratios after : min = %0.15lf, max = %0.15lf\n", min_ratio_after, max_ratio_after );
}
/* Special case for L4/L5: confirm velocity vectors are 60 degrees apart. */
if (point == 4 || point == 5)
{
double speed, angle, arcmin_error;
double mx, my, mz;
double px, py, pz;
double min_angle = NAN;
double max_angle = NAN;
for (i = 0; i < mb.length; ++i)
{
m = mb.array[i];
p = lp.array[i];
/* Calculate unit vector in direction of the minor body's velocity. */
speed = sqrt(m.vx*m.vx + m.vy*m.vy + m.vz*m.vz);
mx = m.vx / speed;
my = m.vy / speed;
mz = m.vz / speed;
/* Calculate unit vector in the direction of the Lagrange point's velocity. */
speed = sqrt(p.vx*p.vx + p.vy*p.vy + p.vz*p.vz);
px = p.vx / speed;
py = p.vy / speed;
pz = p.vz / speed;
/* The dot product should always be very close to 0.5 (an angle of 60 degrees). */
angle = ArcCos(px*mx + py*my + pz*mz);
arcmin_error = 60.0 * ABS(angle - 60.0);
if (arcmin_error > 0.0026)
FAIL("C LagrangeJplAnalyzeFiles(%d, %s): velocity angle is out of bounds: %0.16lf (error = %0.4le arcmin)\n", i, lp_filename, angle, arcmin_error);
if (i == 0)
{
min_angle = max_angle = angle;
}
else
{
if (angle < min_angle)
min_angle = angle;
if (angle > max_angle)
max_angle = angle;
}
}
printf(" speed angles: min_angle = %0.15lf, max_angle = %0.15lf, spread = %0.4le\n", min_angle, max_angle, max_angle - min_angle);
}
fail:
FreeStateVectorBatch(&mb);
FreeStateVectorBatch(&lp);