# Can known object be used to back-calculate my location?

I apologize if this is in the wrong forum. Wasn't sure to put it here or navigation.

Say I have a map, and on it, I know the range and bearing/heading of a known object. Is it possible to somehow back-calculate MY position on the map? Obviously if I know the range to the object is say 50m, then of course I'm 50m away. But is it possible to find my exact location with the other information given? I get bearing and heading confused, so I put both there depending on which would make more sense to have.

## 2 Answers

If you know absolute angle between you and the object relative to a fixed direction (such as north), then yes, otherwise, no. However, in that sense, you have, in effect, another point of reference, but this one is infinitely far away.

• So assuming I know which way true north is, I could figure it out? – pfinferno Nov 24 '14 at 0:52
• Yes. Because what you then have is a new origin for a coordinate system. You need two pieces of information to find your 2D position, so that you have 2 equations and 2 unknowns. If you reference from true east, you have the equivalent of polar coordinates. :) – FundThmCalculus Nov 24 '14 at 2:33
• Is there a specific formula for this? I've been looking around but couldn't find anything. I know that true north will be a known factor in all this. – pfinferno Dec 1 '14 at 12:45

Using the definitions given here, the object's bearing relative to you is sufficient, but your heading is generally not. (However, your heading would be sufficient if you knew you were traveling directly toward the object, since then your heading is the same as the object's bearing. If there is drift involved then you will need this information as well.)

Your bearing relative to the object is also obviously sufficient, if the object has a heading, then it is in motion; you can't use that to find your location.