Following on from my post,
Tag history interpolation - not returning interpolated values, I would like to propose a better and more obvious interpolation.
In a discussion with support the summary was,
Basically, interpolation will only occur before an aggregate is applied if the time slice specific doesn't contain any data points, in which case a single data point will be interpolated for that time slice. This behavior isn't what you want, since you're looking for the points at the start and end of the time slice to be interpolated.
So for one project where I wanted the hourly counts (on an always incrementing count tag) I have had to set the time period to 1 minute to force the return of interpolated values and then run a transform to return every 60th value. It shouldn't be this hard. The system should be able to interpolate on request and return the boundary (period start and end) values. Adding a "difference" function (to return the difference between successive interpolated values rather than the values themselves) would also be extremely useful.
I appreciate that I could take readings on the hour (and have done for certain projects) but that requires additional work and loses the data compression of the historian.