How would you calculate an estimate of earth's circumpolar circumference using coordinates from your GPS?

Answer 1

This will provide an estimate, but it would be fun to see how close this method would bring you. Of course, you could simply look up the answer, but the process here involves the fun of estimating the distance with a little hands-on effort. Your GPS has to be capable of giving you your location in map coordinates.

Find a stretch of highway that is as straight as you can reckon; usually the stretches where you can check your mileage readings are straight. In fact, stretches where there are mileage markers by the tenth of a mile would be ideal. If you find a stretch that is true N-S, you are golden. If not you can still calculate an estimate.

Guarantee that you can do this with complete safety, and without violating any regulations, or putting any individuals or property at risk.

Pull over at a marker near the beginning of your straight stretch of road; record the marker indication, and record your location in coordinates.

Drive as far as you can on your straight stretch, as long as there is a marker you can stop at. Stop after a mile (or more if you can manage it), record the marker, and record your location in coordinates.

With this information you can construct a right triangle with the line you drove as the hypotenuse. Work your coordinates so that you can express the N-S leg in, say, a decimal fraction of degrees latitude, or in other units if you prefer. Do the same for the E-W leg of the triangle to get degrees longitude.

Calculate the number of degrees that would represent the length of the hypotenuse (yes, degrees Lat and degrees Long are not necessarily equal where you are-- this is an estimate). Using the distance calculated from the mileage markers, figure the length of a degree, and multiply that length by 360.

Your estimate will probably be closer to the accepted length the closer you are to the equator. Can you predict whether your estimate will get smaller or larger, the farther away from the equator you are?

If you find a true N-S stretch of highway, just calculate what you estimate to be the length of a degree based on your coordinates off-set and the markers you used, and multiply a degree of length by 360.