Monday, June 27, 2005

How hard is it for the “Common Man” to use the Poor Man’s GPS mentioned earlier?

Many of the readers quickly grasped how the users with a camera phone or with just a cellphone might use the system. However the common question was how will a person without these use these reach their destination? Some even asked if he needs to know pythogoras theorem or distance formula from analytical geometry. So here is my answer.

Latitudes: A degree of latitude always corresponds to about 111 km. So if there is difference of one in the first decimal point of the latitude, it corresponds to a difference of ~10 km. If the difference is 3 then the difference is something like ~30km. If the numbers differ on the second decimal point of the latitude by 5, the difference is like 5 km. On the third, it is like 100m per digit change. On the fourth it is like a 10m change and on the fifth it is like a one meter change.

Longitudes: A degree of longitude corresponds to a distance from 0 to 111 km depending on how far away it is from the equator. For a certain city or town these differences shall be negligible between different parts except for places like the North and south pole which are very sparsely inhabited. We just need to multiply the difference in longitudes with a constant which applies to that city. For cities and places close to the equator, we can treat it just like we trated the latitude, assuming approximately that each digit change in the first decimal place of the longitude meant a 10km difference. Each digit change in the second place meant one km and so on… As you go up you could compute the changes as 3/4, 1/2,1/4th and so on.

That way you don’t have to actually do any serious multiplication division etc. And any way you are never going to the destination through the shortest path or geodesic. So you can coolly add the two numbers you found out earlier i.e the diff b/w longitudes in km and the same for latitudes and just tell yourself roughly how far you are from your destination. You also always know whether you destination lies towards your north or south, east or west. So moving around is more like Golf. First you hit far away and as you keep getting closer to your destination, you start hitting more carefully. It does not need any extra ordinary brilliance to move around the city with some simple heuristics about big barriers like rivers, major highways etc. and some common sense along with the co-ordinates of your target scribbled in your addressbook and co-ordinates imprinted on various objects like mailboxes of houses, power poles etc..