Add FlannIndex abstract interface and implement NanoFlannIndex subclass (#1744)

* Add FlannIndex abstract interface and implement NanoFlannIndex subclass

* Refactored: made NanoFlann a new NN type instead of inheriting FlannIndex. Added tests. Vendoring nanoflann.h directly in the repo. RegistrationVis now use NANOFLANN_INDEX_KDTREE_SINGLE (instead of FLANN_INDEX_KDTREE_SINGLE) flann index for 2d points matching.

* cleanup comments, added FlannIndex doxygen

* Fixing windows tests

* updating flaky test

* Simplified interface, added flann kdtree single approach selectable by parameters.

* RegVis: symmetry of nanoflann for two branches of guess feature matching

* cv::BFMatcher baseline

* Small cmake optimization FLANN_KDTREE_MEM_OPT only defined for FlannIndex

* Refactored where FLANN_KDTREE_MEM_OPT is defined

* fixed file name already exist

* cleanup

* fixup build

---------

Co-authored-by: matlabbe <[email protected]>

corelib/src/rtflann/config.h.in

@@ -35,4 +35,11 @@
 #endif
 #define FLANN_VERSION_ "1.8.4"
 
+// Generated by CMake from config.h.in, as upstream flann does. Carrying the
+// option here rather than in a compile definition keeps a toggle of it from
+// rebuilding the whole library: a definition given to the compiler lands in the
+// target's flags, which every object file depends on, while this header is only
+// included where rtflann is.
+#cmakedefine FLANN_KDTREE_MEM_OPT
+
 #endif /* RTABMAP_FLANN_CONFIG_H_ */

corelib/src/rtflann/defines.h

@@ -29,7 +29,7 @@
 #ifndef RTABMAP_FLANN_DEFINES_H_
 #define RTABMAP_FLANN_DEFINES_H_
 
-#include "config.h"
+#include "rtflann/config.h" // generated by CMake
 
 #ifdef FLANN_EXPORT
 #undef FLANN_EXPORT