With the release of PI Vision and its symbols library, we are trying to move away from ProcessBook. However, one major feature PI Vision still seems to be missing is the ability to do calculations, like PB's 'PI Calc' ability. For example, we wanted to do simple addition of two tag values: generated power from a CHP plant + imported power from the utility co. = Total Power. The way things currently are, this requires either a) creating a ProcessBook display and importing it into PI Vision or b) adding a calculation in AF using Asset Analytics or an attribute formula. Both options require access to a work station with PB and/or System Explorer installed on it, whereas PI Vision can be accessed from anywhere.
I've seen a couple of custom symbols for simple values, but nothing for calculations. After some searching, PI Web API seems to be the best (or only) way to go, so I've come up with https://<server>/piwebapi/calculation/summary/?webID=s0JU52ag55YUORaOBzWLzbswT1NJVEVTVDAyMA&time=*&expression='CHP.Power'%2B'Utility.Power'&summaryType=total as my request . However, I've taken a look at Using PI Web API Client library in PI Vision 2016 R2 and 2017 and I don't understand which portion of the code decides what the request is. Additionally, according to Question - Coresight Symbol Extension with Multiple data source using AF heading as input., a Value symbol can only have a single data source. I envision dragging and dropping one attribute and then another on top of it (like you would to add two attributes to a trend) to populate which tags to add, but I don't want a table - I want it to be a single value.
As my knowledge of PI Web API dates back to about 10am this morning, I'm hoping someone could point me in the right direction. Where does the request go within the code for a custom symbol? Is there a way to make it look like a value, even though they can only have a single data source?