wifi position indoors/inside buildings?

i want to create an application that is able to detect the users position inside buildings but i'm unsure where to start. The actual 'map' i believe it will be just an imagine and the iphone position tracker will be overlayed on top of it (or is there a particular way to deal with this). I believe that the position of the user will be tracked via wifi - but i have done some research into this and it seems that the minimum amount of wifi points needs to be 3+? in order to triangulate the position. (also how accurate will this be?). I saw on the app store a few applications that track the p开发者_JAVA技巧osition of the user inside supermarkets, how is this done? Would appreciate some help on this, any articles/tutorials you could share would be of great value :]. Thanks ..

Take a look at Core Location. It's the framework that provides positioning and GPS info for your app. Its precision is not likely to be fine enough to tell exactly where in a single building you are.