stuff:		is a general library containing utilities to manipulate
       		strings, to open files and other unsorted components.  

core:  		this is the base library of g2o

math_groups:	classes to represent some domainsfor variables used by 
		the types. These are for example SE2, SE3, Sim3, 
		ProjectiveCamera.

types: 		Here are some types plugins for g2o, organized as
		application domain.  This is the list:

		slam2d: types for 2d SLAM. The vertices can represent
		robot poses and point landmarks. The edges can
		represent pose-pose constraints, pose-landmark
		constraints, and pose-landmark (bearing only)
		constraints.
			
		slam3d: types for 3D slam. The vertices can represent
		robot poses with 6dof and the constraints can
		represent pose-pose constraint.
		
		sim3: types for representing an unknown-scale SLAM
		problem.  the vertices represent elements of sim3 (3d
		pose + scale), and the edges represent constraints
		spatial constraints between these sim3 vertices.

		sba: types for bundle adjustment. The vertices include
		intrinsic camera parameters, 3D points, extrinsic
		parameters.  The edges include: monocular projection,
		monocular projection with parameters (3-edge), stereo
		projection and scale constraint between extrinsic
		nodes.  There are also types for BA that are based on
		the exponential map parameterization.

		icp: hmmmm dunno what this is....

solvers:	Here are the linear solver plugins: PCG, colamd, and CHOLMOD.

examples: 	Application examples. These dirs build executables
		
		ba: a simple demo on bundle adjustment that constructs
		a simulated scene and optimizes it
		
		tutorial_slam2d: a complete tutorial on how to build a
		slam2d subsystem. It does not require the types
		plugins, as it defines everything from scratch.

		icp: ???
		
apps: 		here are the main applications that use g2o. they
		include a command line interface and a gui
		application.  
