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.
Syntax
| Visual Basic (Declaration) | |
|---|---|
Overloads Function ReadAtTime( _ ByVal timeStamps() As Date, _ ByVal serverHandles() As Integer, _ ByRef itemValues As OPCHDAItem(), _ ByRef errors As Integer() _ ) As Integer | |
| C# | |
|---|---|
int ReadAtTime( DateTime[] timeStamps, int[] serverHandles, out OPCHDAItem[] itemValues, out int[] errors ) | |
Parameters
- timeStamps
- The timestamps for the requested data.
- serverHandles
- The list of server item handles for the items to be read.
- itemValues
- Array of objects in which the item values are returned. The order of the objects in the array shall be the same as the order of the server item handles.
- errors
- Array of HRESULTs indicating the success of the individual item reads. The errors correspond to the handles passed in phServer. This indicates whether the read succeeded in obtaining a defined value, quality and timestamp. NOTE that any FAILED error code indicates that the corresponding OPCHDA_ITEM struct is undefined.
Return Value
HRESULTS success/error code.Requirements
Target Platforms: Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows 7, Windows Server 2008 family