The Interpolated algorithm calculates a value that uses:
- the last raw historic value before the start of the sample. For the purposes of this section, we will refer to the last raw historic value before the start of the sample as the ‘last pre-sample’ historic value.
If there is a value exactly at the start of the sample then this value (and quality) is used and no interpolation is performed.
and:
- the next raw historic value after the ‘last pre-sample’ historic value. The ‘next’ value may be in the sample or could be after the sample.
If there is no ‘next’ raw historic value, then there is no interpolated value (quality is 'no data'.
To perform the interpolated calculation, Geo SCADA Expert takes the ‘last pre-sample’ calculation and the ‘next’ raw historic value after that, and creates an estimated value that is between the two. This calculation is the equivalent of Geo SCADA Expert drawing a line between the ‘last pre-sample’ value and the ‘next’ raw historic value on a trace, with the result being the point where the start of the sample crosses that line.
The results returned by the algorithm do not depend on the quality of the data. You can choose to filter the data on quality using the Qualities combo box in the Edit Source window (see Configure a Trace)
Interpolated values are useful when there are known gaps in the data. This is because Geo SCADA Expert uses a value outside of the sample in its interpolated calculation, and so it can still return a result, even if there are no raw historic values in the sample (in this case, Geo SCADA Expert returns the last raw historic value from before the sample as the integrated value).
A Trend is configured to show a raw historic trace, and the X-Axis shows 10 minutes, starting at 12:00:00, with markers every 24 seconds. There are raw historic values for the first 3 minutes and 36 seconds and the last 2 minutes 48 seconds, but there are no raw historic values for the between 12:03:36 and 12:07:12.
To calculate the integrated value for the sample, Geo SCADA Expert uses the last value before the start of the sample and the next value after that. In this case, the next value is the first value after the end of the sample. It then calculates the interpolated value, which corresponds to the point at the start of the sample where a line between the ‘last pre-sample’ value and the next value would meet.
Further Information