Sunday, June 19, 2005

Bringing Global Co-Ordinates Indoors.

As every one knows, GPSes don't work indoors, To fix this we can use some new technology we haven't implemented yet. Possibly using beacon signals, Signals from Cell Phone towers etc. But the incentive to reuse existing technologies is very high. Let me explain a way through which my earlier suggestion of snappable barcoded co-ordinates can be extended to work inside buildings.

If you have not read my previous post titled "The Poor Man's GPS" this post might not make sense to you. That aricle discusses how Camera Phones without GPS capabilities can be used as a "virtual GPS unit" by taking snaps of barcoded co-ordinates imprinted all over the world on all kinds of immovable objects like buildings,doors,lamp posts, road signs etc.

One way to achieve this could be a position sensing device wrt. to a fixed point (maybe using sound, radio signals etc) within the building. Then use GPS to determine some points outside the building for reference. The co-ordinate spraying device I discussed in "The Poor Man's GPS" post could be extended in this manner to be used inside buildings. Remember this is a one time activity. Once the co-ordinates are imprinted, all one needs to do is just use a camera phone to find out the co-ordinates one is at.

Another source of co-ordinates info could be CAD files created by the Architects of those buildings.

Have you heard of photogrammetry? Check out In fact they have some very interesting (though a bit dragging for a nerd) videos of creating 3D models from photographs taken from arbitrary directions. The guys at Google are doing something similar by driving thru and creating a 3D model of San Fransisco. The same thing can be done with a building like a hospital, airport, historical site, resort, office building etc. Once you have a 3D model you can determine the co-ordinate of any door knob or speck of dust. If you know the GPS co-ordinate of even a few points(I guess 3) in the building the rest can be trivially determined.