# _moveterm(wtab, noon, width, height) - update illuminated portion of the globe.
sub _moveterm {
    my ($wtab, $noon, $width, $height) = @_;
    my $illumMap = Imager->new(ysize => $height, xsize => $width);
    $illumMap = $illumMap->convert(preset => 'addalpha');
    my $day = Imager::Color->new(255, 255, 255, 10);
    my ($i, $j, $oh, $nl, $nh);
 
    for ($i = 0; $i < $height; $i++) {
        if ($wtab->[$i] >= 0) {
            $nl = (($noon - ($wtab->[$i] / 2)) + $width) % $width;
            $nh = ($nl + $wtab->[$i]) - 1;
 
            $oh = ($nh - $nl) + 1;
            if (($nl + $oh) > $width) {
                for ($j = $nl; $j < $width; $j++) {
                    $illumMap->setpixel(x => $j, y => $i, color => $day);
                }
                for ($j = 0; $j < ((($nl + $oh) - $width) + 1); $j++) {
                    $illumMap->setpixel(x => $j, y => $i, color => $day);
                }
            } else {
                for ($j = $nl; $j < (($nl + $oh) + 1); $j++) {
                    $illumMap->setpixel(x => $j, y => $i, color => $day);
                }
            }
        }
    }
 
    return $illumMap;
}