we currently ignore these pings, which does give us decent headway calculations but can produce holes in our records. as far as i can tell, theres 3 types of stop id outages we tend to see
short stretch outages, which occur for less than a minute and tend to happen at the beginning/end of the stop. these are short enough that we could probably ignore them and have reasonable calculations, even if they happen in the middle of a trip.
medium stretch outages, which occur for maybe 2-10 minutes at a time. we see these a lot on the 39 (potentially caused by a glitchy AVL) and they can cause us to lose information for a couple of stops.
long stretch outages, which might be because the AVL for a vehicle wasn't turned on but GPS was still reporting info.
if a vehicle has been dark for more than ~a minute, we should start trying to interpolate its progress along its shape if possible. there will probably be some complexity wrt
small route diversions
figuring out the inbound/outbound direction of the trip, if that's null (we might be able to grab this from gtfs? or just use previous ping info)
how to store shape information in-memory for quick enough calculations without ballooning memory usage (maybe just cache the more problematic route shapes)
monitoring the duration of a vehicle's outage in order to kick off this calculation
determining whether an event is an arrival or a departure (or neither.) i havent seen any STOPPED_AT events in these outages, and its unclear if the vehicles actually making any stops and not reporting it.
fairly regularly (5000ish times maybe), we will get gps pings from vehicles that reporting their route information, but not their upcoming stop. here's a map of ~2000 such pings over the course of a day https://www.google.com/maps/d/u/0/edit?mid=1ttstvWGxhXTY62ZOA7YYQr-o3Srnbj8&usp=sharing
we currently ignore these pings, which does give us decent headway calculations but can produce holes in our records. as far as i can tell, theres 3 types of stop id outages we tend to see
if a vehicle has been dark for more than ~a minute, we should start trying to interpolate its progress along its shape if possible. there will probably be some complexity wrt
STOPPED_ATevents in these outages, and its unclear if the vehicles actually making any stops and not reporting it.