The PROWL system uses a simple categorisation system to identify what real-world objects are. The category is assigned as a single letter to each polygon object, and groups objects into a type that indicates how it should be handled.
Stationary objects such as buildings are grouped together – these objects are unlikely to move, and so a drone can get relatively close to them. When the database is cleansed, small differences are tolerated between user-submitted objects and the existing data in the PROWL database.
Objects such as wires and trees can be moved by the wind, and so a wider recommended distance is given. When object simplification is performed, a larger tolerance of differences between crowd-sourced data is allowed.
Some objects are categorised as having an expiry date – such as requests for privacy. This expiry date limits data corruption or injection problems, and issues related to temporary changes.
Object categorisation techniques also assist with object simplification; where a stationary object – such as a bridge – and a corridor object – such as a rail line – can be interpreted as not being able to intersect. In this example, if there were multiple user submissions of the bridge object, then the polygons submitted can be simplified to make the bridge model more accurate, but would not be combined with the rail corridor object.
Each object is also assigned a unique ID, the submission date and the submitter username (or source) is recorded as the object owner. This allows the object to be removed by the owner, external data ownership to be retained, and trends in invalid data submissions to be tracked.