view release on metacpan or  search on metacpan

lib/Astro/Coords.pm  view on Meta::CPAN

  # our start time

  # calculate the required times
  my $mtime;
  if ($event == 1 || $event == -1) {
    # previous or next
    $mtime = $self->_calc_mtime( $reftime, $event );

    # Reset the clock
    $self->datetime( $oldtime );

  } elsif ($event == 0) {
    # nearest requires both
    my $prev = $self->_calc_mtime( $reftime, -1 );
    my $next = $self->_calc_mtime( $reftime,  1 );

    # Reset the clock (before we possibly croak)
    $self->datetime( $oldtime );

    # calculate the diff
    if (defined $prev && defined $next) {
      my $prev_diff = abs( $reftime->epoch - $prev->epoch );
      my $next_diff = abs( $reftime->epoch - $next->epoch );

      if ($prev_diff < $next_diff) {
        $mtime = $prev;
      } else {
        $mtime = $next;
      }

    } elsif (defined $prev) {
      $mtime = $prev;
    } elsif (defined $next) {
      $mtime = $next;
    } else {
      croak "Should not occur in meridian_time\n";
    }
  } else {
    croak "Unrecognized value for event: $event\n";
  }

  return $mtime;
}

sub _calc_mtime {
  my $self = shift;
  my ($reftime, $event ) = @_;

  # event must be 1 or -1
  if (!defined $event || ($event != 1 && $event != -1)) {
    croak "Event must be either +1 or -1";
  }

  # do we have DateTime objects
  my $dtime = $self->_isdt();

  # Somewhere to store the previous time so we can make sure things
  # are iterating nicely
  my $prevtime;

  # The current best guess of the meridian time
  my $mtime;

  # Number of times we want to loop before aborting
  my $max = 10;

  # Tolerance for good convergence
  my $tol = 1;

  # Increment (in hours) to jump forward each loop
  # Need to make sure we lock onto the correct transit so I'm
  # wary of jumping forward by exactly 24 hours
  my $inc = 12 * $event;
  $inc /= 2 if (defined $self->name && lc($self->name) eq 'moon');

  # Loop until mtime is greater than the reftime
  # and (mtime - prevtime) is smaller than a second
  # and we have not looped more than $max times
  # There is probably an analytical solution. The problem is that
  # the apparent RA depends on the current time yet the apparent RA
  # varies with time
  my $count = 0;
  print "Looping..............".$reftime->datetime."\n" if $DEBUG;
  while ( $count <= $max ) {
    $count++;

    if (defined $mtime) {
      $prevtime = _clone_time( $mtime );
      $self->datetime( $mtime );
    }
    $mtime = $self->_local_mtcalc();
    print "New meridian time: ".$mtime->datetime ."\n" if $DEBUG;

    # make sure we are going the correct way
    # since we are enforced to only find a transit in the direction
    # governed by "event"

    # Calculate the difference in epoch seconds before the current
    # object reference time and the calculate transit time.
    # Use ->epoch rather than overload since I'm having problems
    # with Duration objects
    my $diff = $reftime->epoch - $mtime->epoch;
    $diff *= $event; # make the comparison correct sense
    if ($diff > 0) {
      print "Need to offset....[diff = $diff sec]\n" if $DEBUG;
      # this is an earlier transit time
      # Need to keep jumping forward until we lock on to a meridian
      # time that ismore recent than the ref time
      if ($dtime) {
        $mtime->add( hours => ($count * $inc));
      } else {
        $mtime = $mtime + ($count * $inc * Time::Seconds::ONE_HOUR);
      }
    }

    # End loop if the difference between meridian time and calculated
    # previous time is less than the acceptable tolerance
    if (defined $prevtime && defined $mtime) {
      last if (abs($mtime->epoch - $prevtime->epoch) <= $tol);
    }
  }