iOS with Parse: users tracking each other

Question

Please suggest the most efficient approach to implement different users tracking each other on the map, so every user can see others current location and they can see his. For example: if one user moves, other immediately see his new location and vice versa. If the user moves and new users appear in his vicinity, they are tracked. I would like to use Parse as a backend for this.

I tried the approach of saving new location on didUpdateUserLocationand then running a query in background, configured as myQuery.whereKey("location", nearGeoPoint: currentGeoPoint, withinKilometers: 0.5)

It works but apparently uses lots of bandwidth, as even a small change in user location triggers a query to Parse (and i see internet activity indicator on iPhone status bar working all the time). So i have a feeling that it can be way more efficient.

Should i use push notifications instead? If so, what would be the implementation in general?

Thanks a lot!

Answer 1

If you want to monitor location changes in realtime, then this will of course require a substantial amount of interaction with the remote server. While Parse may or may not be a good backend for this task, you should keep in mind that, if you are using the free plan, you have a limit of 30 API requests/second (and this may easily be exceeded in this scenario when you have multiple users).

Limiting the updates to significant location changes may be a reasonable compromise, as described in the documentation. Here, you would get a new location when the user moved ~500m, but this could of course be the downside when you want to literally follow the user in person.

Using push notifications to inform other users of a user's location changes might be more efficient:

1. send a push notification to the followers once a user changes her/his location. This would mean one request for each location change.
2. update other users' location changes when your own location changes. Here you would have two requests for each location change.

Using 1, you would still get updates from other users, even when you are not on the move. Note that these requests are counted for the device, not for Parse. I.e. Parse includes sending push notifications in the request limit.