c#: Distance from point to a line segment (in longitude and latitude)

I have a position (A) in longitude and latitude.

I have a line segment with start (B) and end (C) points in longitude and latitude.

What I am trying to calculate is the shortest distance from A to lin开发者_Python百科e B<->C. In other words the distance from A to the closest point (on line BC) in meters.

Thanks in advance.