This method reads the values and qualities from the history database for the specified timestamps for one or more items. This method is intended to provide values to correlate with other values with a known timestamp. For example, the values of sensors when lab samples were collected. The order of the values and qualities returned shall match the order of the time stamps supplied in the request. When no value exists for a specified timestamp, a value shall be interpolated from the surrounding values to represent the value at the specified timestamp. The interpolation will follow the same rules as the standard Intpolated aggregate as outlined in Section 2.9 of the OPC HDA specification. The OPCHDA_ITEM structure will return OPCHDA_NOAGGREGATE in the aggregate field. If a value is found for the specified timestamp, the server will set the OPCHDA_RAW bit in the quality. If the value is interpolated from the surrounding values, the server will set the OPCHDA_INTERPOLATED bit in the quality.
Overload List
| Overload | Description |
|---|---|
| ReadAtTime(DateTime[],Int32[],OPCHDAItem[],Int32[]) | Synchronous ReadAtTime. This method reads the values and qualities from the history database for the specified timestamps for one or more items. This method is intended to provide values to correlate with other values with a known timestamp. For example, the values of sensors when lab samples were collected. The order of the values and qualities returned shall match the order of the time stamps supplied in the request. When no value exists for a specified timestamp, a value shall be interpolated from the surrounding values to represent the value at the specified timestamp. The interpolation will follow the same rules as the standard Intpolated aggregate as outlined in Section 2.9 of the OPC HDA specification. The OPCHDA_ITEM structure will return OPCHDA_NOAGGREGATE in the aggregate field. If a value is found for the specified timestamp, the server will set the OPCHDA_RAW bit in the quality. If the value is interpolated from the surrounding values, the server will set the OPCHDA_INTERPOLATED bit in the quality. |
| ReadAtTime(Int32,DateTime[],Int32[],Int32,Int32[]) | Asynchronous ReadAtTime. This method reads the values and qualities from the history database for the specified timestamps for one or more items. This method is intended to provide values to correlate with other values with a known timestamp. For example, the values of sensors when lab samples were collected. The results are returned via the client's IOPCHDA_DataCallback::OnReadComplete method. The order of the values and qualities returned shall match the order of the time stamps supplied in the request. When no value exists for a specified timestamp, a value shall be interpolated from the surrounding values to represent the value at the specified timestamp. The interpolation will follow the same rules as the standard Intpolated aggregate as outlined in Section 2.9 of the OPC HDA specification. The OPCHDA_ITEM structure will return OPCHDA_NOAGGREGATE in the aggregate field. If a value is found for the specified timestamp, the server will set the OPCHDA_RAW bit in the quality. If the value is interpolated from the surrounding values, the server will set the OPCHDA_INTERPOLATED bit in the quality. |
Requirements
Target Platforms: Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows 7, Windows Server 2008 family