I’m using Ignition 8.0.14 and I think the noInterpolation parameter for system.tag.queryTagHistory() is not working correctly.
I have configured a tag to be historized in the following way.
If I change the value tag, for example from 125 to 130, the function system.tag.queryTagHistory(), with returnSize = 0 and noInterpolation = True, returns interpolated values. Why?
What do you expect to be returned with a
returnSize = 0?
There are scenarios where, rather than throwing an error, the historian will fall back to some ‘default’ query logic (I didn’t write the system, and changing it at this point would be a breaking change) - it seems like that’s what you’re encountering, because asking for a
returnSize of 0 doesn’t make any sense.
According to the documentation:
So, the historian is making a decision, because you’re giving it contradictory information. Natural return mode by definition requires interpolation - so it’s discarding the
noInterpolation flag you’re setting in favor of the explicit
Ok, so I think that the documentation should clarify that if the “returnSize = 0” parameter is used then interpolation will be done and the “noInterpolation” parameter will have no effect. Thus, the information is clearer for all users.