Geofencing Extension API Developer's Guide

Asset Distance and Search Radius

For each polygon geofence that covers the asset position or is close to it, the Geofencing Extension API returns the geofence geometry together with the asset's distance to this geometry.

The asset distance can be influenced by the following factors:
  • The asset is outside of the geofence – the distance is the straight line to the closest border of the geofence. This is always the case for line and point geofences.
  • The asset is inside the geofence – the distance is the straight line to the closest border of the polygon, with a negative sign.
  • The asset is outside of the search radius – the geofence is not listed in the response.
  • The asset is inside the polygon but further away from the border of the search radius – a special value indicating "far inside" is returned.

In your application, you can use the asset distance to generate events with different severity levels based on specific distance thresholds. You can also suppress superfluous events if the asset is moving along the geofence border, such as, entering or leaving the geofence frequently without a significant change in the asset distance.

For performance reasons, the asset distances are only straight line distances, not equivalent to driving distances or driving times. Asset distances are limited to approximately 20 kilometers, so a distance can be one of the following:
  • within the polygon 250m from the closest border
  • within the polygon more than 20km from the closest border
  • outside the geofence 333m from the closest border
  • outside the geofence more than 20km from the closest border (this value applies to all non-listed geofences, when the asset is outside of the search radius)

Events such as entering, leaving, flickering along the border of the geofence, or re-entering the geofence do not receive an explicit response; only the asset distances. The same applies to a sequence of events, such as the asset entering the geofence for the third time or leaving for the second time on the same day.

Note: Currently, the Geofencing Extension API does not require or support asset identification or registration.