Script to interpolate minor stop times using the surrounding
major stops.

This takes a stop_times.txt file from a google transit feed
and outputs a new file stop_times_interpolated.txt with the
missing stop times filled in.

Original use was for the Wellington GTF when they stopped
including minor stop times.

Interpolates using the shape_dist_traveled assuming the buses
are moving at a constant speed. Interpolated stops are given
the same departure and arrival time and times are rounded to
the nearest minute.

Output file should be the same as the input, but with the
missing times added and with unix line endings.

Example input (stop_times.txt):

trip_id,arrival_time,departure_time,stop_id,stop_sequence,stop_headsign,pickup_type,drop_off_type,shape_dist_traveled
1,06:58:00,06:58:00,22018,2,,0,1,0
1,,,22557,3,,0,1,39
1,,,22559,4,,0,1,76
1,,,22560,5,,0,1,130
1,07:02:00,07:02:00,21984,62,,1,0,157
2,07:04:00,07:04:00,23129,1,,0,1,0
2,,,22026,6,,0,1,68
2,,,22027,7,,0,1,117
2,,,22028,8,,0,1,159

Example output (stop_times_interpolated.txt):

trip_id,arrival_time,departure_time,stop_id,stop_sequence,stop_headsign,pickup_type,drop_off_type,shape_dist_traveled
1,06:58:00,06:58:00,22018,2,,0,1,0
1,06:59:00,06:59:00,22557,3,,0,1,39
1,07:00:00,07:00:00,22559,4,,0,1,76
1,07:01:00,07:01:00,22560,5,,0,1,130
1,07:02:00,07:02:00,21984,62,,1,0,157
2,07:04:00,07:04:00,23129,1,,0,1,0
2,07:07:00,07:07:00,22026,6,,0,1,68
2,07:09:00,07:09:00,22027,7,,0,1,117
2,07:10:00,07:10:00,22028,8,,0,1,159