I am having a difficult time trying to figure out how to add feet to a latitude and longitude because I am very unfamiliar with lat and long coordinates. I have found several formulas to try and convert latitude and longitude to feet but I am not sure which ones are correct. For example, this website: http://www.colorado.edu/geography/gcraft/warmup/aquifer/html/distance.html I am not sure how to use or apply this method.
I have the latitude and longitude of two points and I want to be able to find the vector of the points. I believe I have to convert the latitude and longitude to feet in order for this to work. Can anyone please help me out in trying to figure this out?
Best Answer
You can use the results given in that website to good approximation as long as the distance between your two points is much less than the radius of the Earth.
If your two points are $A$ and $B$ and their latitudes and longitudes are $\lambda_A$, $\phi_A$, and $\lambda_B$, $\phi_B$ ($\lambda$ is lat, $\phi$ is lon) then the distance between them in latitude is 69.172mi $\times$ ($\lambda_B - \lambda_A$). (I am assuming $\phi_A$ and $\phi_B$ are in degrees.)
Distance in longitude is a bit more complicated. The latitudes $\lambda_A$ and $\lambda_B$ should not differ by very much. (Which is a consequence of what I said above, that the distance between the two points should be much smaller than the radius of the Earth.) If this is the case, we can settle on a "compromise" $\lambda_C = (\lambda_A+\lambda_B)/2$. Then, distance in longitude is
$69.172$ mi $\times \cos (\lambda_C) \times (\phi_B - \phi_A)$.
Again, I am assuming that all angle are in degrees. I am also assuming you will have a $\cos$ function that calculates in terms of degrees.
So now you have your distance in lat and your distance in lon, so there's your vector. If you calculate as I describe, your numbers will be in miles. To get feet, multiply them both by 5280 ft/mi.