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Photomap - how it works

If the location of photos are known they can be overlayed on a map at the correct position. This section describes a way of recording longitude, latitude, orientation, date and time information in the filename of a digital photo. It enables them to be located anywhere in the world to accuracy of one metre, and in time to one second.

One millionth of a degre equals ten centimetres.

An arc of one millionth of a degree equates to about 10cm at the Earth's surface.

How many decimal places of longitude and latitude are needed to narrow a photo down to 1 metre accuracy on the Earth's surface?

Earth bulges at the equator, and so it is there that one degreee of longitude or latitude covers the most distance on the ground. Earth's equatorial diameter is 12,756.3 km. Assuming everything is perfectly spherical this gives a circumference of 12756.3 x pi = 40075.098km. Therefore 1 metre subtends (/ 360 40075098.0) = 0.00000898 degrees. That figure then is the minimum accuracy needed to identify 1 metre. Rounding this down to 0.000001 degrees (six decimal places: a millionth of a degree) gives accuracy of about 10 cm at the Earth's surface.

So, Lattitude can go from -90.000000 to +90.000000 and Longitude from -180.000000 to 180.000000. URLs do not like the + symbol, so n, s, e, and w are used instead of plus and minus symbols.

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