formula to determine distance between GPS LOCs?

[hartmut77]

Hi

I have heard that there is a formula to determine the distance between two

gps ( latitude and longitude ) values. Does anyone know about this or have a sample file where they use this? Thanks

Dave

[BobWeaver]

What you are looking for is called the great circle distance formula:

Distance=arccos(sin(LatitudeLocation1)*sin(LatitudeLocation2)+cos(LatitudeLocation1)*cos(LatitudeLocation2)*cos(LongitudeLocation2-LongitudeLocation1))*60

This formula is from my old HP-21 calculator manual. I think the result is in miles. Filemaker's trig functions require the Latitude and Longitude values to be in radians, not degrees. So you may need to use the Radian() function to convert from degrees, and Filemaker doesn't have an arccos() function. You can derive it with the sin cos and atan function, but I have forgotten the formula. Maybe someone else can help out here.

[Vaughan]

Wow Bob, I'm impressed. You still have the *manual* from an HP-21!

[BobWeaver]

I never throw anything out. I still have the manual. I see you still have 5 stars. Wanna trade?

In fact I still have the calculator. Old HP's never die!

[djgogi]

ASIN(x)=Int(Degrees(ATAN((1/SQR(1-x^2))))

ACOS(x)=Int(Degrees(ATAN(SQR((1-x^2)/x^2))))

Dj

[BobWeaver]

Dj, is there a reason why you put everything inside the Int() function?