Biometrics Class (POS for .NET v1.12 SDK Documentation)
2/27/2008
Defines the programmatic interface for a UPOS Biometrics device.
Namespace: Microsoft.PointOfService
Assembly: Microsoft.PointOfService (in microsoft.pointofservice.dll)
Syntax
'Declaration
Public MustInherit Class Biometrics
Inherits PosCommon
public abstract class Biometrics : PosCommon
public ref class Biometrics abstract : public PosCommon
public abstract class Biometrics extends PosCommon
public abstract class Biometrics extends PosCommon
Remarks
Biometrics devices capture data by using a biometrics sensor. The biometrics data is encoded in Biometrics Information Records, each of which contains one or more Biometrics Data Blocks which in turn contain one or more biometric data samples or biometric templates.
This standard model uses the term template, as adapted from the BioAPI to refer to the biometric enrollment data for a user. The term Biometric Information Record refers to any biometric data that is returned to the application. This includes raw data, intermediate data, processed samples ready for verification or identification, and enrollment data. Typically, the only data that is stored persistently by the application is the Biometrics Information Record generated for enrollment.
The format of the Biometric Data Blocks is indicated by the Format field of the Header. This may be a standard or proprietary format. In this case, the Biometric Data Block may be encrypted. The digital signature is optional, and may be used to verify integrity of the data during transmission and storage. When present, the digital signature is calculated on the Header and the Biometric Data Block. For standardized Biometrics Information Record formats, the signature would take a standard form, but, for proprietary Biometrics Information Record formats, the signature can take any form that suits the Service. Therefore, there is no C structure definition of the signature. The Biometrics Information Record Data Type indicates whether the Biometrics Information Record is signed and encrypted or only encrypted.
Capabilities
All Biometrics devices have the following capabilities:
The device can capture Biometrics data for enrollment. The notion of enrollment requires better quality for the final Biometrics Information Record that is created. Generally, the Biometrics Information Record aggregates a series of biometric captures.
The device may capture Biometrics data for verification. Verification does not require the same level of quality as enrollment.
The device can determine whether two Biometrics Information Records match within the degree of error specified by the False Accept Rate (FAR) and False Reject Rate (FRR). The FAR is the margin of percentage error acceptable that two nonmatching biometric samples are falsely regarded as not matching.
The device can compare a Biometrics Information Record against a sample population of Biometrics Information Records and create a rank ordering of the population for identification.
Some Biometrics devices may have the following additional capabilities:
- The device returns the raw biometric data in "real time" as it is captured by the device. If this capability is true and has been enabled by the application having set the RealTimeDataEnabled property to true, a series of StatusUpdateEventare queued, each as a raw image representing a partial biometrics image capture.
Programming Model
The Biometrics device usage model is as follows:
The Biometrics Device follows the general Device Input Model for event driven input:
When input is received by the Service, it queues a DataEvent event.
If AutoDisable is true, the Device automatically disables itself when a DataEvent event is queued.
A queued DataEvent event can be delivered to the application when the property DataEventEnabled is true and other event delivery requirements are met. Just before delivering this event, data is copied into properties, and additional data events are disabled by setting DataEventEnabled to false. This causes later input data to be queued while the application processes the current input and associated properties. When the application has finished processing the current input and is ready for more data, it re-enables events by setting DataEventEnabled to true.
A ErrorEvent event is queued if an error occurs while collecting or processing input, and is delivered to the application when DataEventEnabled is true and other event delivery requirements are met.
The DataCount property may be read to obtain the number of queued DataEvent events.
All queued input may be deleted by calling the ClearInput method.
Deviations from the general Device Input Model for event-driven input are as follows:
The capture of biometrics data begins when the BeginEnrollCapture or BeginVerifyCapture method is called.
If biometrics capture is stopped by calling EndCapture then no DataEvent or ErrorEvent events will be queued.
Device Sharing
The Biometrics device is exclusive-use, as follows:
The application must claim the device before the application enables it.
The application must claim and enable the device before the application accesses many of the Biometrics specific properties.
The application must claim and enable the device before the application calls methods that manipulate the device or before the application changes some writable properties.
Platforms
The Biometrics class requires POS for .NET version 1.10 or later versions.
Inheritance Hierarchy
System.Object
Microsoft.PointOfService.PosDevice
Microsoft.PointOfService.PosCommon
Microsoft.PointOfService.Biometrics
Microsoft.PointOfService.BasicServiceObjects.BiometricsBasic
Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread-safe. Any instance members are not guaranteed to be thread-safe.