Calculated Properties

CPs can modify and combine incoming data using numeric, string and time-based operations, do unit conversion, select and combine properties, convert latitude/longitude into distance, integrate and differentiate ...and much more.

How-to Articles

• Introducing Calculated Properties
• How Calculated Properties work (a look under the hood)`
• Discover all the capabilities of Calculated Properties

Points to note about Calculated Properties

1. See the expression syntax used throughout DevicePilot including in CPs, including how to 'escape' property names which contain non-alphanumeric characters.
2. $ts values are in milliseconds
3. You can’t use CPs within CPs
4. Like normal properties, a CP is defined the same across all devices, but when it’s evaluated for a particular device it is calculated purely from other properties of that device. It can’t see the values of properties in other devices - to do that kind of analysis you need to use a KPI.
5. Because a CP is calculated every time any of its inputs changes it can be used to merge event streams. But be careful that in some cases it can cause event duplication: if you have a CP which copies events from other properties, but is gated by the state of a third property, then a change in that third property will also cause a CP event.
6. If a CP uses $previous then any properties it uses must always be set together (i.e. in the same message). So if your CP is e.g. "y - $previous/x" then x and y must always be set in the same message, otherwise $previous/x may sometimes return undefined.
7. Whitespace is ignored --- so feel free to use newlines & tabs/spaces to make structure clear.