CMake Error at F:/Download/opencv_contrib-master/modules/dnn/cmake/download_protobuf.cmake:23 (ocv_download):
Unknown CMake command "ocv_download".
Call Stack (most recent call first):
F:/Download/opencv_contrib-master/modules/dnn/cmake/download_protobuf.cmake:51 (ocv_protobuf_download)
F:/Download/opencv_contrib-master/modules/dnn/cmake/OpenCVFindLibProtobuf.cmake:30 (include)
F:/Download/opencv_contrib-master/modules/dnn/CMakeLists.txt:35 (include)
这个错误是什么意思啊，是ovc_download这行代码无法识别吗？ 怎么修改才能使编译通过啊？
