The class ``SURF_GPU`` implements Speeded Up Robust Features descriptor. There is a fast multi-scale Hessian keypoint detector that can be used to find the keypoints (which is the default option). But the descriptors can also be computed for the user-specified keypoints. Only 8-bit grayscale images are supported.
The class ``SURF_GPU`` can store results in the GPU and CPU memory. It provides functions to convert results between CPU and GPU version ( ``uploadKeypoints``, ``downloadKeypoints``, ``downloadDescriptors``). The format of CPU results is the same as ``SURF`` results. GPU results are stored in ``GpuMat``. The ``keypoints`` matrix is :math:`\texttt{nFeatures} \times 6` matrix with the ``CV_32FC1`` type.
*``keypoints.ptr<float>(SF_X)[i]`` contains x coordinate of the i-th feature.
*``keypoints.ptr<float>(SF_Y)[i]`` contains y coordinate of the i-th feature.
*``keypoints.ptr<float>(SF_LAPLACIAN)[i]`` contains the laplacian sign of the i-th feature.
*``keypoints.ptr<float>(SF_SIZE)[i]`` contains the size of the i-th feature.
*``keypoints.ptr<float>(SF_DIR)[i]`` contain orientation of the i-th feature.
*``keypoints.ptr<float>(SF_HESSIAN)[i]`` contains the response of the i-th feature.
The ``descriptors`` matrix is :math:`\texttt{nFeatures} \times \texttt{descriptorSize}` matrix with the ``CV_32FC1`` type.
Brute-force descriptor matcher. For each descriptor in the first set, this matcher finds the closest descriptor in the second set by trying each one. This descriptor matcher supports masking permissible matches between descriptor sets. ::
The class ``BruteForceMatcher_GPU`` has an interface similar to the class :ocv:class:`DescriptorMatcher`. It has two groups of ``match`` methods: for matching descriptors of one image with another image or with an image set. Also, all functions have an alternative to save results either to the GPU memory or to the CPU memory. The ``Distance`` template parameter is kept for CPU/GPU interfaces similarity. ``BruteForceMatcher_GPU`` supports only the ``L1<float>``, ``L2<float>``, and ``Hamming`` distance types.
:param trainIdx:Output single-row ``CV_32SC1`` matrix that contains the best train index for each query. If some query descriptors are masked out in ``mask`` , it contains -1.
:param distance:Output single-row ``CV_32FC1`` matrix that contains the best distance for each query. If some query descriptors are masked out in ``mask``, it contains ``FLT_MAX``.
:param trainCollection::ocv:class:`gpu::GpuMat` containing train collection. It can be obtained from the collection of train descriptors that was set using the ``add`` method by :ocv:func:`gpu::BruteForceMatcher_GPU::makeGpuCollection`. Or it may contain a user-defined collection. This is a one-row matrix where each element is ``DevMem2D`` pointing out to a matrix of train descriptors.
:param trainIdx:Output single-row ``CV_32SC1`` matrix that contains the best train index for each query. If some query descriptors are masked out in ``maskCollection`` , it contains -1.
:param imgIdx:Output single-row ``CV_32SC1`` matrix that contains image train index for each query. If some query descriptors are masked out in ``maskCollection`` , it contains -1.
:param distance:Output single-row ``CV_32FC1`` matrix that contains the best distance for each query. If some query descriptors are masked out in ``maskCollection`` , it contains ``FLT_MAX``.
:param maskCollection:``GpuMat`` containing a set of masks. It can be obtained from ``std::vector<GpuMat>`` by :ocv:func:`gpu::BruteForceMatcher_GPU::makeGpuCollection` or it may contain a user-defined mask set. This is an empty matrix or one-row matrix where each element is a ``PtrStep`` that points to one mask.
Finds the k best matches for each descriptor from a query set with train descriptors. The function returns detected k (or less if not possible) matches in the increasing order by distance.
:param trainIdx:Output matrix of ``queryDescs.rows x k`` size and ``CV_32SC1`` type. ``trainIdx.at<int>(i, j)`` contains an index of the j-th best match for the i-th query descriptor. If some query descriptors are masked out in ``mask``, it contains -1.
:param distance:Output matrix of ``queryDescs.rows x k`` size and ``CV_32FC1`` type. ``distance.at<float>(i, j)`` contains a distance from the j-th best match for the i-th query descriptor to the query descriptor. If some query descriptors are masked out in ``mask``, it contains ``FLT_MAX``.
:param allDist:Floating-point matrix of the size ``queryDescs.rows x trainDescs.rows``. This is a buffer to store all distances between each query descriptors and each train descriptor. On output, ``allDist.at<float>(queryIdx, trainIdx)`` contains ``FLT_MAX`` if ``trainIdx`` is one from k best.
Downloads ``trainIdx`` and ``distance`` matrices obtained via :ocv:func:`gpu::BruteForceMatcher_GPU::knnMatch` to CPU vector with :ocv:class:`DMatch`. If ``compactResult`` is true, the ``matches`` vector does not contain matches for fully masked-out query descriptors.
For each query descriptor, finds the best matches with a distance less than a given threshold. The function returns detected matches in the increasing order by distance.
:param trainIdx:``trainIdx.at<int>(i, j)`` , the index of j-th training descriptor, which is close enough to i-th query descriptor. If ``trainIdx`` is empty, it is created with the size ``queryDescs.rows x trainDescs.rows``. When the matrix is pre-allocated, it can have less than ``trainDescs.rows`` columns. Then, the function returns as many matches for each query descriptor as fit into the matrix.
:param nMatches:``nMatches.at<unsigned int>(0, i)`` containing the number of matching descriptors for the i-th query descriptor. The value can be larger than ``trainIdx.cols`` , which means that the function could not store all the matches since it does not have enough memory.
:param distance:Distance ``distance.at<int>(i, j)`` between the j-th match for the j-th query descriptor and this very query descriptor. The matrix has the ``CV_32FC1`` type and the same size as ``trainIdx``.
Downloads ``trainIdx``, ``nMatches`` and ``distance`` matrices obtained via :ocv:func:`gpu::BruteForceMatcher_GPU::radiusMatch` to CPU vector with :ocv:class:`DMatch`. If ``compactResult`` is true, the ``matches`` vector does not contain matches for fully masked-out query descriptors.
