Frequently Asked Questions: FAQ about GPS

Topic

8	Distance between two positions

Distance between two positions

Question:

I have two positions in Lat and Lon, and want to find out the distance between them.

Answer:

For short distances, one can take the line of sight between the two points:

Say you have two points: (Lat1, Lon1) and (Lat2 and Lon2) which are not too far (kilometers) from each other.

- Take the differences:

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dLat = Lat1 - Lat2
dLon = Lon1 - Lon2
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- Convert these to meters:

One degree of Latitude has 111'199.233 Meters:

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dMLat = dLat * 111'199.233
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One degree of Longitude is dependent on the Latitude. One degree Longitude has 111'199.233 * cosine ( Latitude ) Meters. Please note that usually, the cosine library function expects it argument in radians, rather than degrees, so conversion might be necessary.

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dMLon = dLon * ( 111'199.233 * cos ( Lat * PI / 180 ) )
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- We now have the differences in meters in north/south direction dMLat, and in east/west direction dMLon. Using Pythagoras, we get the true distance

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D = square_root( dMLon² + dMLat² )
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Keep in mind that this is only true for relatively short distances. For longer distances, the "Great Circle" algorithm can be used, which is documented in literature.

Further Information

FAQ about GPS

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last modified: 06.10.2004

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