How do I convert two g . p. s . readings to feet measurement ?

Question

I have two g. p.s. readings and would like to know how many feet they are apart ?

Answer 1

Let First location be with co-ordinate LAT1 and LON1
second location be LAT2 and LON2
where LAT is lattitude and LON is longitude

LAT on the nothern hemisphere is +ve and southern -ve
similarly LOngitude on easter side of GMT line is +ve and west is -ve

LAT LON units are in radians

The shortest distance connecting these two points on earth would virtually cut the globe into equal halfs. In other words the shortest distance when stretched around the globe is called the GREAT CIRCLE.

Now using the spherical cordinate system we can derive the distance between these two co-ordinates.
RADIUS=radius of earth (~6378.7 KM)

Distance can be found out by finding out the subtended angle between the radii(from earth centre) joining those two GPS points and the arc distance is found by multiplying the angle by radius.
DIST=RADIUSx[ACOS(COS(LAT1)
*COS(LON1)*COS(LAT2)*COS(LON2)
+COS(LAT1)*SIN(LON1)
*COS(LAT2)*SIN(LON2)
+SIN(LAT1)*SIN(LAT2))]

DIST is distance in KM
Convert the KM to feet using conversion

If the distance between these points is short a flat earth model can be used which saves computation time.

Answer 2

is that gallons per second or global positioning satellite