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require "/usr/local/lib/";
$observer = Astro::Nova::LnLatPosn->new("lng"=>-106,"lat"=>35);
$rst = get_body_rst_horizon2(2456614,$observer,\&get_lunar_equ_coords, 1/8.);
debug($rst->get_rise(), $rst->get_transit(), $rst->get_set());
=item get_body_rst_horizon2($jd, $observer, $get_body_equ_coords, $horizon)
For Julian day $jd and observer $observer, give the rise/set/transit
times of body whose coordinates are given by the function
$get_body_equ_coords; rise and set are computed relative to $horizon
NOTE: $jd should be an integer
TODO: assumes bodys elevation is fairly unimodal
TODO: what is get_dynamical_time_diff() and why do I need it?
TODO: handle multiple rise/sets in a given day
TODO: this subroutine is slow; can speed up (at expense of accuracy)
by tweaking findmax/findmin
sub get_body_rst_horizon2 {
my($jd, $observer, $get_body_equ_coords, $horizon) = @_;
# thing Im going to return
my($ret) = Astro::Nova::RstTime->new();
# TODO: this should be a parameter or something (1/86400. = 1 sec)
my($precision) = 1/1440.;
# body's ra/dec at $jd+.5
my($pos) = &$get_body_equ_coords($jd+.5);
# local siderial time at midday JD (midnight GMT, 5pm MST, 6pm MDT)
my($lst) = fmodp(get_apparent_sidereal_time($jd+.5)+$observer->get_lng()/15,24);
# approximate transit/zenith time of body (as fraction of day)
my($att) = fmodp(0.5+($pos->get_ra()/15-$lst)/24,1);
# fairly inaccurate (but that's OK) nadir time
my($atn) = fmodp($att+.5,1);
# altitude of body (above horizon) for $observer at given time
my($f) = sub {get_hrz_from_equ(&$get_body_equ_coords($_[0]), $observer, $_[0])->get_alt()-$horizon};
# the max altitude should occur within 6h of the approximate transit
# time, but disallow crossing the day line
my($s) = $jd + max($att-.25,0);
my($e) = $jd + min($att+.25,1);
my($maxtime) = findmax($f, $s, $e, $precision);
my($maxalt) = &$f($maxtime);
# same for min altitude
$s = $jd + max($atn-.25,0);
$e = $jd + min($atn+.25,1);
my($mintime) = findmin($f, $s, $e, $precision);
my($minalt) = &$f($mintime);
# circumpolar conditions (recall $f gives elevation ABOVE horizon)
if ($maxalt < 0) {return -1;}
if ($minalt > 0) {return +1;}
# if $mintime < $maxtime, find rise efficiently, set inefficiently
if ($mintime < $maxtime) {
$rise = findroot($f, $mintime, $maxtime, $precision);
# set may occur from start of day to nadir or zenith to end of day
# TODO: it can actually be BOTH!
$set = findroot($f, $jd, $mintime, $precision);
# if that returned nothing...
unless ($set) {$set = findroot($f, $maxtime, $jd+1, $precision);}
} else {
# if $maxtime < $mintime, find set efficiently, rise inefficiently
$set = findroot($f, $maxtime, $mintime, $precision);
# rise is from start of day to zenith or from nadir to end of day
$rise = findroot($f, $jd, $maxtime, $precision);
unless ($rise) {$rise = findroot($f, $mintime, $jd+1, $precision);}
# TODO: this could be more efficient methinks
# TODO: I can return more here, including maxalt, minalt, nadir time, etc
return $ret;