Best fit retrieval

For the " best fit" retrieval mode, the total time for the query is divided into even sub-periods, and then up to five values are returned for each sub-period:

• First value in the period

• Last value in the period

• Minimum value in the period, with its actual time

• Maximum value in the period, with its actual time

• The first "exception" in the period (non-Good quality)

"Best fit" retrieval allows for a compromise between delta retrieval and cyclic retrieval. For example, delta retrieval can accurately represent a process over a long period of time, as shown in the following trend. However, to achieve this representation, a large number of data values must be returned.

If cyclic retrieval is used to retrieve the data, the retrieval is much more efficient, because fewer values are returned. However, the representation is not as accurate, as the following trend shows.

"Best fit" retrieval allows for faster retrieval, as typically achieved by using cyclic retrieval, plus the better representation typically achieved by using delta retrieval. This is shown in the following trend.

For example, for one week of five-second data, 120,960 values would be returned for delta retrieval, versus around 300 values for best-fit retrieval.

Best-fit retrieval uses retrieval cycles, but it is not a true cyclic mode. Apart from the initial value, it only returns actual delta points. For example, if one point is both the first value and the minimum value in a cycle, it is returned only one time. In a cycle where a tag has no points, nothing is returned.

As in cyclic retrieval, the number of cycles is based on the specified resolution or cycle count. However, the number of values returned is likely to be more than one per cycle.

All points are returned in chronological order. If multiple points are to be returned for a particular timestamp, then those points are returned in the order in which the corresponding tags were specified in the query.

The best-fit algorithm is only applied to analog and analog summary tags. For all other tags, delta results are returned.