What exactly do you want to calculate ?
If it's the angle, in degrees, of the height difference between 2 points?
You need the distance between the 2 points and the height difference.
The angle is:
adeg = Atan(diff_heigth/distance)*180/cPi
To calculate the distance between the 2 points, the calculation depends on the units of the 2 points.
If the units are long and lat, the distance is calculated :
ang = 2*ASin(Sqrt(Sin((lat2-lat1)/2)*Sin((lat2-lat1)/2)+Cos(lat1)*Cos(lat2)*Sin((long2-long1)/2)*Sin((long2-long1)/2)))
EarthRadiusKm=6371.01
Distance=EarthRadiusKm*ang
Best regards.