[PCL]keypoint

1. Harris角点

http://www.cnblogs.com/ironstark/p/5064848.html

2. ISS关键点

http://www.cnblogs.com/ironstark/p/5069311.html

3. NARF

http://pointclouds.org/documentation/tutorials/narf_keypoint_extraction.php#narf-keypoint-extraction