CIFaceFeature的所有属性都是只读的，请问自己创建一个实例，怎样初始化它的值啊？谢谢

[benbenRH]

请教一问题，我新建一个CIFaceFeature对象：

CIFaceFeature *feture = [[CIFaceFeature alloc]init];

这个CIFaceFeature的所有属性都是只读的，请问自己创建一个实例，怎样初始化它的值啊？谢谢！

CIFaceFeature的定义如下（苹果的官方定义）：

/** A face feature found by a CIDetector.
 All positions are relative to the original image. */
CORE_IMAGE_CLASS_EXPORT
@interface CIFaceFeature : CIFeature
{
	CGRect bounds;
	BOOL hasLeftEyePosition;
	CGPoint leftEyePosition;
	BOOL hasRightEyePosition;
	CGPoint rightEyePosition;
	BOOL hasMouthPosition;
	CGPoint mouthPosition;
	
    
	BOOL hasTrackingID;
	int trackingID;
	BOOL hasTrackingFrameCount;
	int trackingFrameCount;
	
	BOOL hasFaceAngle;
	float faceAngle;
	
	BOOL hasSmile;
	BOOL leftEyeClosed;
	BOOL rightEyeClosed;
	
}

/** coordinates of various cardinal points within a face.
 
 Note that the left eye is the eye on the left side of the face
 from the observer's perspective. It is not the left eye from
 the subject's perspective. */

@property (readonly, assign) CGRect bounds;
@property (readonly, assign) BOOL hasLeftEyePosition;
@property (readonly, assign) CGPoint leftEyePosition;
@property (readonly, assign) BOOL hasRightEyePosition;
@property (readonly, assign) CGPoint rightEyePosition;
@property (readonly, assign) BOOL hasMouthPosition;
@property (readonly, assign) CGPoint mouthPosition;

@property (readonly, assign) BOOL hasTrackingID;
@property (readonly, assign) int trackingID;
@property (readonly, assign) BOOL hasTrackingFrameCount;
@property (readonly, assign) int trackingFrameCount;

@property (readonly, assign) BOOL hasFaceAngle;
@property (readonly, assign) float faceAngle;

@property (readonly, assign) BOOL hasSmile;
@property (readonly, assign) BOOL leftEyeClosed;
@property (readonly, assign) BOOL rightEyeClosed;

@end