public SiftFeature(VlSiftKeypoint keypoint, SiftKeyPointOrientation[] keypointOrientations)
{
this.keypoint = keypoint;
this.keypointOrientations = keypointOrientations;
}
/// <summary>
/// 进行SIFT检测，并返回检测的结果
/// </summary>
/// <param name="im">单通道浮点型图像数据，图像数据不必归一化到区间[0,1]</param>
/// <param name="resultType">SIFT检测的结果类型</param>
/// <returns>返回SIFT检测结果——SIFT特征列表；如果检测失败，返回null。</returns>
public unsafe List<SiftFeature> Process(IntPtr im, SiftDetectorResultType resultType)
{
//定义变量
List<SiftFeature> features = null; //检测结果：SIFT特征列表
VlSiftFilt siftFilt; //
VlSiftKeypoint* pKeyPoints; //指向关键点的指针
VlSiftKeypoint keyPoint; //关键点
SiftKeyPointOrientation[] orientations; //关键点对应的方向及描述
double[] angles = new double[4]; //关键点对应的方向（角度）
int angleCount; //某个关键点的方向数目
double angle; //方向
float[] descriptors; //关键点某个方向的描述
IntPtr ptrDescriptors = Marshal.AllocHGlobal(128 * sizeof(float)); //指向描述的缓冲区指针
//依次遍历每一阶
if (VlFeatInvoke.vl_sift_process_first_octave(ptrSiftFilt, im) != VlFeatInvoke.VL_ERR_EOF)
{
features = new List<SiftFeature>(100);
while (true)
{
//计算每组中的关键点
VlFeatInvoke.vl_sift_detect(ptrSiftFilt);
//遍历每个点
siftFilt = (VlSiftFilt)Marshal.PtrToStructure(ptrSiftFilt, typeof(VlSiftFilt));
pKeyPoints = (VlSiftKeypoint*)siftFilt.keys.ToPointer();
for (int i = 0; i < siftFilt.nkeys; i++)
{
keyPoint = *pKeyPoints;
pKeyPoints++;
orientations = null;
if (resultType == SiftDetectorResultType.Normal || resultType == SiftDetectorResultType.Extended)
{
//计算并遍历每个点的方向
angleCount = VlFeatInvoke.vl_sift_calc_keypoint_orientations(ptrSiftFilt, angles, ref keyPoint);
orientations = new SiftKeyPointOrientation[angleCount];
for (int j = 0; j < angleCount; j++)
{
angle = angles[j];
descriptors = null;
if (resultType == SiftDetectorResultType.Extended)
{
//计算每个方向的描述
VlFeatInvoke.vl_sift_calc_keypoint_descriptor(ptrSiftFilt, ptrDescriptors, ref keyPoint, angle);
descriptors = new float[128];
Marshal.Copy(ptrDescriptors, descriptors, 0, 128);
}
orientations[j] = new SiftKeyPointOrientation(angle, descriptors); //保存关键点方向和描述
}
}
features.Add(new SiftFeature(keyPoint, orientations)); //将得到的特征添加到列表中
}
//下一阶
if (VlFeatInvoke.vl_sift_process_next_octave(ptrSiftFilt) == VlFeatInvoke.VL_ERR_EOF)
break;
}
}
//释放资源
Marshal.FreeHGlobal(ptrDescriptors);
//返回
return features;
}