Figure ground distance from GPS coordinates?

[dwilson]

I want to take the GPS data from my GRT data dumps and figure distance from one point to the next. Does anyone know a slick easy way to do it?

Thanks,
Duane

[asav8tor]

http://gc.kls2.com/

[Radomir]

If you're looking for something with a higher geek factor, take a look at this site:


http://williams.best.vwh.net/avform.htm

[jmartinez443]

You can throw the Lat/Long into an excel spreadsheet and apply this formula for the distance:

d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos (lon1-lon2))

[az_gila]

Originally Posted by jmartinez443

You can throw the Lat/Long into an excel spreadsheet and apply this formula for the distance:

d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos (lon1-lon2))

Jorge... isn't there a constant missing from your formula (possibly the radius of the earth?)

gil A

[szicree]

You gotta multiply that whole thing by radius to get the answer.

[DGlaeser]

Originally Posted by az_gila

Jorge... isn't there a constant missing from your formula (possibly the radius of the earth?)

gil A

Actually no. A nautical mile is equal to 1 great circle arc minute on the earth's surface. So once you know the angle, you know the mileage

[szicree]

Originally Posted by DGlaeser

Actually no. A nautical mile is equal to 1 great circle arc minute on the earth's surface. So once you know the angle, you know the mileage

Wouldn't this still require multiplying by 60? Additionally, Excel gives the output in radians, requiring conversion to degrees first if this approach is to be used.

[az_gila]

Originally Posted by DGlaeser

Actually no. A nautical mile is equal to 1 great circle arc minute on the earth's surface. So once you know the angle, you know the mileage

Ahh... but you didn't state any units.... - and most people would use degrees for angles, not minutes ...... just like most GPS boxes output....

This is the formula the FAI use for aviation record calculations for great circle distance (from the SSA web site) - use 7-8 digit accuracy in your calculations...

Q:
What is the Great Circle Distance formula and how do I apply it to my flight?

A:
The formula is:

Distance = K ~ arccos([sin A * sin B] + [cosA * cos B * cos(X - Y)])

A = North latitude of the departure point (or Lat A)
X = West longitude of the departure point (or Long X)
B = North latitude of the destination (or Lat B)
Y = West longitude of the destination (or Long Y)
K = conversion factor from degrees to distance
= 69.09332414 (the FAI value of K resulting in statute miles).

gil A

SSA = Soaring Society of America - above lat/long assumes North America area and the use of decimal degrees

[az_gila]

This web site will calculate great circle distances and draw a course line on a Google map/satellite picture.

It does recognize three letter airport codes...

http://www.acscdg.com/

gil A