(GNSS stands for Global Navigation Satellite System and is the generic term that covers GPS and other similar services that may be used by your device to determine its current location.)
Using the average of a series of GNSS locations can result in a potentially more accurate location than simply using a single location from the GNSS. NB: There is no guarantee of the actual accuracy achieved. It is simply more likely to be more accurate than a single GNSS location.
Bit Map can use GNSS Location Averaging for taking Waypoints and for recording new features to an existing map layer. Refer to the documentation for those features regarding how to invoke GNSS Location Averaging:
- Tracking and Waypoints – Record Location(s) as Tracks and Waypoints
- Add a New Feature to an Existing Layer
Following the Location Averaging in either of the above procedures will display the ‘Location Averaging’ view.
Collect and Average a Series of GNSS Locations
In the ‘Location Averaging’ view:
- Enter the number of GNSS locations to collect for averaging
- (minimum is 10, 100 or more is recommended)
- Place the device on a flat, stable surface and do not move it while it is collecting
- Best results are achieved in locations with a clear view of the sky, well away from buildings, cliffs, trees, etc
- Tap ‘Start Collecting’
The number of locations collected will be displayed and updated as they are collected.
Once the required number of locations has been collected, the ‘Location Averaging’ view will disappear, and the averaged location will be passed back to the procedure from which it was requested (ie, a new Waypoint or a new Feature point/vertex in an existing Map Layer).
How GNSS Location Averaging Works in Bit Map
Once the ‘Start Collecting’ button has been tapped, Bit Map will prevent the device from entering sleep (idle) mode, and will begin checking every GNSS location that it receives. If the horizontal accuracy of any GNSS location is less than or equal to 5 metres, it will be added to the pool of locations which will be used for averaging (if it is greater than 10 metres, the location will be ignored).
When the pool of locations reaches the number of locations to be collected for averaging (as entered in the field in the ‘Location Averaging’ view), then Bit Map will stop collecting GNSS locations.
Bit Map will then check for outliers within the pool. If any location in the pool is further than 5 metres from the nearest other location, then it will be ignored (effectively removed from the pool). Note that the z coordinate (elevation/altitude) is ignored for this calculation.
If the number of locations remaining in the pool is more than half of the number required to be collected, the Bit Map will generate a new location with the average x coordinate, average y coordinate and average z coordinate of all the locations remaining in the pool. The new location will use the timestamp from the last location collected.
This new location will be returned to the calling procedure (New Waypoint or New Feature point/vertex).