Piccadilly Line Trains
Data feed…
https://api.tfl.gov.uk/trackernet/PredictionSummary/P?
Location (L=) strings missing the actual locations, as shown here…
T S=“242” T=“32” D=“372” C=“15:00” L=“” DE=“Rayners Lane” AT=“” DT=“17:37:00”
Without these being updated my app kind of messes up 
So it looks like this is caused by certain non-passenger locations not having an associated location “description”.
Looking at the live data right at the moment, I’ll use Piccadilly line train 222 as an example…
In the detailed predictions for Acton Town:
TrackCode property), but unlike the train above it, this entry is missing a Location property to describe where this track is.
So unsurprisingly, if you look at the summary prediction for the same train, the L (location) property is blank:
From intertube, we can see this train is currently at Acton Town East Sidings:
The reason that intertube has a description for this location is that eta has done a lot of work on observing trains as they move on the network, and making assumptions and guesses on what a specific location may be based on the observed behaviour.
Realistically, if you have a blank location field, then in most cases it would be fairly safe to assume that that train is at a non-passenger location like a siding or depot.
yep, thanks for that explanation, however i don’t normally get a blank location on any of my trains on any line up until now and that is why i mentioned it.
As for sidings and depots etc. well they do actually appear in most of the location strings, they certainly do on the Bakerloo line because at one point i even showed them moving into and out of depots (Stonebridge Park) and sidings (Queens Park, Harrow & W, etc.) on my display but decided to scrap it because it cluttered up even more than it already is and would probably be confusing to some users.
And as for the Trackcode property well that appears in a feed i am not currently accessing, the reason for that is because i want to keep the number of feeds i access down to a minimum, although that could change in the future depending on what information i need.
As I said at the very top of my response, this would be due to certain specific track sections not being annotated with a description - I am by no means saying that no sidings or depot locations have been labelled, as I have seen many of them in the data feed myself.
If you haven’t encountered one before then consider yourself quite lucky, as I had at one point observed around 50-odd track sections without a description. I can’t seem to locate my list anymore, but there’s a chance that some of them have been rectified by now anyway.
However, what I do know is that most, if not all, areas that a passenger train can be found on have been labelled, hence it being a safe assumption that a blank location is a non-passenger track section.
Correct - If you wanted to make use of the track section codes, you would need to do what intertube does and poll a significantly larger number of API endpoints to be able to fetch all trains while using the detailed predictions.
@HighTrainsDrifter
Acton Town is a rare destination for the Piccadilly Line these days, which may explain why you have not bumped up against it previously.
It was common when I was young, along with Barons Court and Green Park. Those were the days when the platform indicators just said Uxbridge Line or Hounslow Line, the Heathrow service not then having, er, taken off.
