Added Features2d::limitKeypoints() with grid options. Odometry: if imu is provided and no guess is provided, the change of orientation of imu is used for rotation guess (overwrite rotation from Odom/GuessFromMotion). OdometryInfo: added gravity errors when imu is used. Preferences: added a second GravitySigma parameter (overwritting Optimizer/GravitySigma for odometry is not negative) for F2M odometry panel.

corelib/src/Rtabmap.cpp

@@ -3132,6 +3132,8 @@ bool Rtabmap::process(
 				UINFO("Set loop closure transform = %s", loopIter->second.transform().prettyPrint().c_str());
 				statistics_.setLoopClosureTransform(loopIter->second.transform());
 
+				statistics_.addStatistic(Statistics::kLoopVisual_words(), sLoop->getWords().size());
+
 				// if ground truth exists, compute localization error
 				if(!sLoop->getGroundTruthPose().isNull() && !signature->getGroundTruthPose().isNull())
 				{