How to convert arc length to km?

My goal is to find a good function to calculate the distance for two points for millions of data points. I found the fucntion lldistkm in the FileExchange. Unfortunately, that function does not seem to work well for column data. It only works well for single data points.

Lon1 = -78.1982;
Lat1 = 33.8282;
 
Lon2 = -77.5003;
Lat2 = 32.8499;
 
Distance_km = lldistkm([Lat1, Lon1],[Lat2, Lon2])
Distance_arc = distance(Lat1, Lon1, Lat2, Lon2)

Here is my question. If I will rely on the Matlab function distance (see above) in the mapping toolbox to calcualte the distance. It's results will be in arc length? How do I convert it from arc length to km? Their ratio should be around 111 depending on the latitude.

So rad2km is the wrong function? It does not give me a number close to 111 at all.

Many thanks.

Answer 1

[Sean de Wolski]

Arc length from the distance function is the distance. It will be in units of the ellipsoid or the value of the fifth input argument:

https://www.mathworks.com/help/releases/R2021a/map/working-with-distances-on-the-sphere.html

[Leon]

It works! That's exactly what I want.

Many thanks.