Download or view vsop87.frink in plain text format
//
// Routines for parsing VSOP87 coefficient files and generating Frink code
// from them (or, with small modifications, for other languages).
// The output of running this program is a partial Frink program
// that contains function definitions to find the coordinates of each planet.
//
// The full coefficients of the VSOP87 theory are available for download
// from:
// ftp://ftp.imcce.fr/pub/ephem/planets/vsop87/
//
// From this, the series we require for use with the equations in Meeus
// are the VSOP87D.xxx files, which contains the
// heliocentric spherical variables referred to equinox and ecliptic of date.
//
// This reverses the lines in the file so that smaller coefficients are
// added first, reducing numerical error.
planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
for planet = planets
{
ext = lc[left[planet, 3]]
firstline = true
fullvar = undef
running = undef
println["""
//
// $planet
//
// This function calculates the heliocentric coordinates of $planet
// referred to the mean equinox *of the date*. You may want to convert this
// to another coordinate system, such as FK5.
//
// arguments:
// d: the date/time to be calculated for
//
// returns:
// [L, B, R]
//
// Where
// L is the heliocentric longitude,
// B is the heliocentric latitude
// R is the distance from the sun.
${planet}HeliocentricCoordinates = {|d|
tau = meeusT[d] / 10
"""]
for line=lines["file:vsop87/VSOP87D.$ext"]
{
if [planet, varno, varnames, exponent] = line =~ %r/VSOP87\s+VERSION\s+D4\s+(\w+)\s+VARIABLE\s+(\d)\s+\((\w+)\)\s+\*T\*\*(\d)/
{
varno = parseInt[varno]
varname = substrLen[varnames, varno-1, 1]
firstline = true
if (fullvar)
println[" $fullvar = $running;\n"]
fullvar = varname+exponent
running = ""
// println["Planet: $planet\tvarno: $varno\tvarname: $varname\texponent: $exponent\tname: $fullvar"]
} else
{
A = eval[substr[line, 79, 97]]
B = eval[substr[line, 97, 111]]
C = eval[substr[line, 111, 132]]
if length[line] != 132
println[length[line]]
// Remove lines with coefficients of 0.0
if (eval[A] != 0.0)
{
running = "$A * cos[$B + $C * tau]" + (firstline ? "" : " +\n ") + running
firstline = false
}
}
}
println["""
$fullvar = $running;
L = ((L0 + L1 tau + L2 tau^2 + L3 tau^3 + L4 tau^4 + L5 tau^5) radians) mod circle
B = ((B0 + B1 tau + B2 tau^2 + B3 tau^3 + B4 tau^4 + B5 tau^5) radians) mod circle
R = (R0 + R1 tau + R2 tau^2 + R3 tau^3 + R4 tau^4 + R5 tau^5) au
return [L, B, R]
}"""]
}
Download or view vsop87.frink in plain text format
This is a program written in the programming language Frink.
For more information, view the Frink
Documentation or see More Sample Frink Programs.
Alan Eliasen was born 20218 days, 0 hours, 12 minutes ago.