How can I detect "enter" and "exit" of roaming geofences?

[Evanfeenstra]

Amazing job with this library, I love working with Tile38!

Is it possible to detect "enter" and "exit" while using FENCE ROAM? Currently it seems like the webhook is triggered with each location update, but I do not see a way to send a hook when the device is no longer nearby the roaming fence.

[tidwall]

I'm glad you're enjoying Tile38!

For FENCE ROAM there's no concept of enter or exit detection. Instead, there are nearby and faraway objects.

For example, open the fence on a terminal:

tile38-cli> NEARBY people FENCE ROAM people * 5000

Then add two points in a second terminal:

tile38-cli> SET people alice POINT 33.02 -115.02
tile38-cli> SET people bob POINT 33.01 -115.01

This will fire off the notifcation:

{
  "command": "set",
  "group": "5c96cfc90970e43f3e56a699",
  "detect": "roam",
  "key": "people",
  "time": "2019-03-23T17:31:05.26178-07:00",
  "id": "bob",
  "object": {"type":"Point","coordinates":[-115.01,33.01]},
  "nearby": {"key":"people","id":"alice","object":{"type":"Point","coordinates":[-115.02,33.02]},"meters":1451.138},
}

which indicates that bob is nearby alice.

Now if we update bob to be far away from alice:

tile38-cli> SET people bob POINT 33.01 -116.01

causes the notification:

{
  "command":"set",
  "group":"5c96cfc90970e43f3e56a699",
  "detect":"roam","key":"people",
  "time":"2019-03-23T17:34:02.911938-07:00",
  "id":"bob",
  "object":{"type":"Point","coordinates":[-116.01,33.01]},
  "faraway":{"key":"people","id":"alice","object":{"type":"Point","coordinates":[-115.02,33.02]},"meters":92314.009}}

You'll notice the there's a faraway object.

One side effect is that you may get a lot of nearby notifications when two objects continue to be nearby each other. If this is a problem then use the NODWELL keyword.

tile38-cli> NEARBY people FENCE NODWELL ROAM people * 5000

This will ensure that there is repeating nearby or faraway notifications for two connecting objects.

I hope this answers your question.

[fas3r]

Hello @tidwall ,

I just found out about tile38 and it's look greats but I have a question about geofencing and precisions, to avoid to open a new thread I prefer to comment here as it's more or less related.

1 ) how close/precise can I get with the radius using "within" for the geofencing ? does ~20meter radius is reasonable ? It's not mention in the documention of INTERSECT or WITHIN for the minimum distance radius.

2 ) What's the best way to manage big set of data ? Meaning if I have 10000 trucks and each of them hold 3000 coordinates**, should I use SET with OBJECT ? And if I need to modify or add a coordinates I would use JSET with RAW ? ( like here

**this could be happen for example if the truck device is not able to send his coordinates becausethe area is not covered ( gsm/3,4G, Sigfox or other...). It keep the coordinates in cache and send them once reconnected.

3 ) If I have predeterminate itinerary (set of coordinates ) from A to B, with a marker every 50 meters ( coordinate ). Is it possible to use WITHIN with multiple coordinates as arguments ? for instance the itinerary from A to B against the SET define in point 2) and the precision of point 1) (~20meters) ? The expected output would be to have all the trucks that did the following itinerate within a radius of ~20meters ( Lower it is, the best it would be..)

I guess I could do a loop but there is maybe better and more efficient way to achieve that.

Sorry for all the questions.

Thanks by advance.

Br, Fas3r.

[Evanfeenstra]

Hi @tidwall, thanks a lot for your answer! NODWELL is exactly what I was looking for