Converting Longitude coordinates to feet (for separation)

[John1397]

TL;DR Summary

I have two longitude decimals readings and they are .11330 apart how many feet is this? One is 98.000000 and other is 98.113300

I have two longitude decimals readings and they are .11330 apart how many feet is this?

 

[BvU]

On the north pole it's zero. Where are you ?

 

[John1397]

On the north pole it's zero. Where are you ?

98 puts it in North Dakota

 

[BvU]

that would be latitude 47 or thereabouts. Latitude matters to convert longitude differences to furlongs!

$\$

 

[BvU]

Here we have 1 degree of longitude = 288200 ft. That's at 38 deg latitude. So for latitude 47 you have $\cos 47/\cos 38$ times 288200 feet per degree of longitude.

Someone should check this

And don't forget to set the calculator to 'degrees' !

$\$

 

[gmax137]

@John1397 you need to figure the circumference at the latitude then divide by 360 to get the arc distance per degree.

 

[jedishrfu]

Here's a calculator that does it for you:

https://www.nhc.noaa.gov/gccalc.shtml

Here's a detailed description of hos the conversion works:

https://www.geeksforgeeks.org/program-distance-two-points-earth/

https://www.thoughtco.com/degree-of-latitude-and-longitude-distance-4070616

 

[jbriggs444]

98 puts it in North Dakota

With the range of latitudes in North Dakota, that leaves an uncertainty of about 800 feet plus or minus for the east/west distance corresponding to .113300 degrees of longitude.

Meanwhile, with six significant figures, that angular measurement claims to be good to within 2.5 inches, plus or minus.

*mumbles to self for a bit... derivative of cosine is sine... latitude around 45 degrees... sine is about .7... *

If your north/south position is off by 4 inches, then your estimate of east/west distance will be less accurate than that angular uncertainty calls for.

*mumbles to self again... *

At the 2.5 inch accuracy level, we need to be worrying about the ellipsoidal shape of the Earth, local topography and the distinction between a great circle and a rhumb line.