Interpolated retrieval

Interpolated retrieval works like cyclic retrieval, except that interpolated values are returned if there is no actual data point stored at the cycle boundary.

This retrieval mode is useful if you want to retrieve cyclic data for slow-changing tags. For a trend, interpolated retrieval results in a smoother curve instead of a "stair-stepped" curve. This mode is also useful if you have a slow-changing tag and a fast-changing tag and want to retrieve data for both. Finally, some advanced applications require more evenly spaced values than would be returned if interpolation was not applied.

By default, interpolated retrieval uses the interpolation setting specified for the tag in the AVEVA Historian. This means that if a tag is set to use stair-step interpolation, interpolated retrieval gives the same results as cyclic retrieval.

Interpolation is only applied to analog tags. If you retrieve data for other types of tags, stair-step interpolation is used, and the results are the same as for cyclic retrieval.

Interpolated retrieval is a bit slower than cyclic retrieval. It shares the limitations of cyclic retrieval in that it may not accurately represent the stored process data.