After a quick search on stackoverflow.com I found the following post http://stackoverflow.com/questions/569980/how-to-calculate-distance-from-a-gpx-file.
Below is my Ruby version of the formula shown in the second post:
This will calculate in meters. To get KM, remove "*1000" on line 3. To get miles, change line 3 to "r = 3959". I'll post the whole GPX parse code in a few days.
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| def haversine(lat1, long1, lat2, long2) | |
| dtor = Math::PI/180 | |
| r = 6378.14*1000 | |
| rlat1 = lat1 * dtor | |
| rlong1 = long1 * dtor | |
| rlat2 = lat2 * dtor | |
| rlong2 = long2 * dtor | |
| dlon = rlong1 - rlong2 | |
| dlat = rlat1 - rlat2 | |
| a = power(Math::sin(dlat/2), 2) + Math::cos(rlat1) * Math::cos(rlat2) * power(Math::sin(dlon/2), 2) | |
| c = 2 * Math::atan2(Math::sqrt(a), Math::sqrt(1-a)) | |
| d = r * c | |
| return d | |
| end |
This will calculate in meters. To get KM, remove "*1000" on line 3. To get miles, change line 3 to "r = 3959". I'll post the whole GPX parse code in a few days.
Hey. You are using a function called power which isnt part of ruby. Care you include it here?
ReplyDeleteThanks!
Hi,
DeleteSorry about that.
Here's the power function:
def power(num, pow)
num ** pow
end
For that function, what do you make num and pow equal to as I can't get my head around it. The line is -
ReplyDeletea = power(Math::sin(dlat/2), 2) + Math::cos(rlat1) * Math::cos(rlat2) * power(Math::sin(dlon/2), 2)
Just confused as to what to declare num and pow as in this instance.
Any help appreciated.
Hi,
DeleteThe power method takes a number and the power, and returns number**power, just as you've described in your other comment.
If you are doing this in Ruby, I'd recommend checking out the geo_magic gem (https://github.com/kristianmandrup/geo_magic)
Just found a slightly different implementation which does the powers manually, would this work instead?
ReplyDeletea = (Math.sin(dlat_rad/2))**2 + Math.cos(lat1_rad) * Math.cos(lat2_rad) * (Math.sin(dlon_rad/2))**2
Many thanks.
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ReplyDelete