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Formula for converting coords to distance?


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Hi...so recently I've found myself in a position of having to navigate by coordinates as opposed to waypoint. While walking around checking the change in my coordinates against the coords that I'm supposed to go to, I found myself wondering what the formula might be for converting Minutes/Seconds to Miles/Feet? e.g. If I see that I am at N 38* 51.233 and I need to get to N38* 52.128 What distance does that represent in Feet or miles?

 

Thanks mucho in advance for the help ;)

Edited by Springsman
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The answer depends on how accurate you want to be. I actually have to do calculations like this as part of my job sometimes. If you assume a flat earth, you can basically use the Pythagorean theorem to determine the distance between two lat/lon locations. This is probably close enough for you since it's a small distance and you're not near either of the poles. For better accuracy over longer distances, you assume a spherical earth and use spherical trigonometry. Not a lot of fun.

 

However, there is a rule of thumb you can use. By definition, one nautical mile (6076 feet approximately) is one minute of longitude at the equator. So for the values you gave, they are a little less than one minute apart, so it should be about 1 mile between them.

 

Hope that helps.

 

Eric.

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http://www.movable-type.co.uk/scripts/latlong.html

 

Not a tidy formula as such, but this webpage lets you enter your two points and it calculates distance and bearing. Further down the page it shows the algorithm it uses. One method is the spherical law of cosines, and you can do this in an Excel cell:

 

=ACOS(SIN(lat1)*SIN(lat2)+COS(lat1)*COS(lat2)*COS(lon2-lon1))*6371

 

That's straight from the webpage, by the way - have a look for more geeky stuff!

 

P.S. That's all in metric by the way...

Edited by tiiiim
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Hi...so recently I've found myself in a position of having to navigate by coordinates as opposed to waypoint. While walking around checking the change in my coordinates against the coords that I'm supposed to go to, I found myself wondering what the formula might be for converting Minutes/Seconds to Miles/Feet? e.g. If I see that I am at N 38* 51.233 and I need to get to N38* 52.128 What distance does that represent in Feet or miles?

 

Thanks mucho in advance for the help ;)

Hello from just up north a short distance in Longmont.

 

At our latitude, you can figure each 0.001 east/west represents about 4 feet. North/south, figure 0.001 represents about 6' (it's more like 6.1'). Those are rounded, so they're more accurate when closer in. So in the case above where you were off by 0.105, that's roughly 630'.

 

Edit: OOPS! I saw the 233 and 128, and didn't pay attention to the 51 vs 52. So it's 1.105, not 0.105 that we're calculating. Still, to get a sense of the distance, you'd add another 6,000 feet (6 x 1000). Call it 6,630' in very rounded terms. More accurately, it would be closer to 6,752 feet.

Edited by ecanderson
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Ummm....

 

Maybe I'm missing something here, but regardless of whether you are navigating in lat/long, UTM, or whatever, why not just make a waypoint of your destination, and then navigate to it? Your GPSr will tell you distance and bearing, updated in real time.

 

Sorry if I am being a bit thick! :rolleyes:

Edited by julianh
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