Save STD descriptors

[ubgaokk]

Thanks for sharing the good work. I am wondering whether it is possible to add the way to save STD descriptors to files in the codes, and for another place recognition, reload STD descriptors from the files.

[OliverShaoPT]

You can save data_base_ using "fwrite()" with iteration and index list, and save plane_cloud_vector_ using "pcl::io::savePCDFileBinary".