This asynchronous function reads the values and qualities from the history database for the specified timestamps for one or more items.
This function 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 ReadComplete event handler.
Syntax
| Visual Basic (Declaration) | |
|---|---|
Public Overloads Function ReadAtTime( _ ByVal transactionID As Integer, _ ByVal timeStamps() As Date, _ ByVal server() As Integer, _ ByRef cancelID As Integer, _ ByRef errors As Integer() _ ) As Integer | |
| C# | |
|---|---|
public int ReadAtTime( int transactionID, DateTime[] timeStamps, int[] server, out int cancelID, out int[] errors ) | |
Parameters
- transactionID
- An identifier created by the client and passed to the server in this call. The server shall return this identifier along with the results of this call.
- timeStamps
- The timestamps for the requested data.
- server
- The list of server item handles for the items to be read.
- cancelID
- OUT: Place to return a Server generated ID to be used in case the operation needs to be canceled.
- errors
- OUT: Array of HRESULTs indicating whether the corresponding server handle was valid.
Return Value
S_OK, S_FALSE, E_NOTIMPL, E_INVALIDARG, E_FAILRemarks
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 specification Section 2.9 .
The OPCHDAitem structure will return OPCHDA_NOAGGREGATE in the aggregate field. If a value is found for the specified timestamp, the server will return OPCHDA_RAW in the quality. If the value is interpolated from the surrounding values, the server will return OPCHDA_INTERPOLATED in the quality.
Requirements
Target Platforms: Windows 7/8/10, Windows Server 2008/2012/2016, .NET 4.x