First, thanks for some very clear technical writing - you are going at just the right speed for me.

External libraries :
Two things I would like to see discussed. Several external libraries are referenced in the source code. For example, openscenegraph and opencv, both of which I tried to install on my Windows 7 and OS X last night without success. The internet has a lot to say on those subjects and given the motivation, I'm sure I would figure it out, but it would be nice to know how they would be used, to calibrate my motivation, or if there a minimal install of compiled libraries to reduce the needed motivation.

using git :
I came across the issue after trying to update my local copy of your repository by doing git pull from the top directory of an older version then following with git submodule init etc as in the Readme.md. cmake failed and started me down the external library path. After starting from a clean clone everything worked fine. Of course, I need to know git better, but if there are a few simple git commands you could layout to do a proper update as a stop gap measure, that would be appreciated.

There have been a number of review comments along the lines of asking for improvements in the instructions for getting set up with the examples, so we're going to try to address that in the next version of the MEAP (or the one after that) and I'll try to update the repo README to make the steps clearer.

The use of OpenCV is limited right now. Some of the examples later in the book might require it, since it provides some cross-platform functionality that isn't otherwise easily available, in particular pulling images from webcams. In the absence of OpenCV, the example project is designed to fall back on an embedded copy of libPNG

OpenSceneGraph usage was just an experiment to see how difficult it would be to work with. It probably shouldn't have made it to the public repository, so I'm sorry if it caused any confusion. I'll take a look at cleaning up the repository and dependencies tonight, since apparently some of my more experimental paths are bleeding through from the private version I'm using for development.