theBorneo

I was wondering if anyone could explain or clear me out -- I am currently doing some project to identify an object e.g. a tree using an android. I suppose the main components I must use at this project is GPS, Camera API and Compass (Please let me know if anyone can think anything) -- I am still in a middle of researching about the project before implement them but the problem I am having is:

If for example if there are two trees are in the same line of sight or same line (overlapping), what information is going to be displayed? How I can tell my software that I am actually facing e.g. north and want to display the front tree not the back of the tree? What sort of information or algorithm will I use to determine this? I mean does the camera or compass or GPS or even the database of the location of tree will determine it? Or do I have to use sensor or some kind of distance degree?

Can anyone please give me some idea, how I can tackle this kind of problem? Or perhaps if anyone know any tutorials that I can learn etc?

Much appreciated.
theBorneo