polyline: Handle trips that pass the same stop ID more than once

		$distance = GIS::Distance->new;

	};

	# Ggf. sollte die Abbildung andersrum laufen: Im zweiten Schritt durch die

	# Polyline iterieren und Stops zuordnen (d.h. polyline_i als Key); bei

	# Bedarf Polyline-Indexe duplizieren. Lässt sich wunderbar an der Linie

	# 101/106 in Essen testen (3x Helenenstr, davon 2x am Anfang und 1x

	# mittendrin).

	if ($distance) {

		my %min_dist;

		# A single trip may pass the same stop multiple times, meaning that

		# stop IDs alone are not guaranteed to be unique. So we need to use a

		# stop's index in the trip's route as key in addition to the stop's ID.

		my $route_i = 0;

		for my $stop ( $self->route ) {

			for my $polyline_index ( 0 .. $#{ $self->{polyline} } ) {

				my $pl   = $self->{polyline}[$polyline_index];

					$stop->{latlon}[1],

					$pl->{lat}, $pl->{lon}

				);

				if ( not $min_dist{ $stop->{id_code} }

					or $min_dist{ $stop->{id_code} }{dist} > $dist )

				my $key = $route_i . ';' . $stop->{id_code};

				if ( not $min_dist{$key}

					or $min_dist{$key}{dist} > $dist )

				{

					$min_dist{ $stop->{id_code} } = {

					$min_dist{$key} = {

						dist  => $dist,

						index => $polyline_index,

					};

				}

			}

			$route_i += 1;

		}

		$route_i = 0;

		for my $stop ( $self->route ) {

			if ( $min_dist{ $stop->{id_code} } ) {

				$self->{polyline}[ $min_dist{ $stop->{id_code} }{index} ]{stop}

			my $key = $route_i . ';' . $stop->{id_code};

			if ( $min_dist{$key} ) {

				if ( defined $self->{polyline}[ $min_dist{$key}{index} ]{stop} )

				{

					# XXX experimental and untested

					# one polyline entry maps to multiple stops → duplicate it; insert $stop after the already-present entry

					$min_dist{$key}{index} += 1;

					splice(

						@{ $self->{polyline} },

						$min_dist{$key}{index},

						0, { %{ $self->{polyline}[ $min_dist{$key}{index} ] } }

					);

				}

				$self->{polyline}[ $min_dist{$key}{index} ]{stop}

				  = $stop;

			}

			$route_i += 1;

		}

	}