Distance Between Points Command

[alleyjo]

Do you have a command that can programatically report the distance between two geodectic points, i.e., longitudes and latitudes, in an XY plot?

[DPlotAdmin]

No, but there isn't that much to it and you can incorporate this into your own code easily enough. In FORTRAN:

Code: Select all

c
c==============================================================================
c
      real*8 function r_earth(lat)
      implicit none
      real*8   lat    ! latitude in radians

      real*8   a, b
      parameter (a=3963.191)    ! equatorial radius in miles
      parameter (b=3949.903)    ! polar radius in miles
      real*8   r

      r = sqrt( ( (a*a*cos(lat))**2 + (b*b*sin(lat))**2 ) /
     1          ( (a*cos(lat))**2   + (b*sin(lat))**2   )
     2        )
      r_earth = r
      return
      end
c
c==============================================================================
c
      real*8 function latlontodistance(lat1, lon1, lat2, lon2)
      implicit none
      real*8 lat1, lon1, lat2, lon2   ! latitude and longitude in degrees

      real*8 lat1r, lat2r, lon1r, lon2r
      real*8 d, pi
      real*8 dlon, dlat, a, c

      real*8 r_earth
      external r_earth

      if((lat1 .eq. lat2) .and. (lon1 .eq. lon2)) then
        d = 0.0
      else
        pi = 4.0*atan(1.D0)
        lat1r = lat1 * pi/1.8D2
        lon1r = lon1 * pi/1.8D2
        lat2r = lat2 * pi/1.8D2
        lon2r = lon2 * pi/1.8D2

c       Haversine formula:

        dlon = lon2r - lon1r
        dlat = lat2r - lat1r

        a = (sin(dlat/2))**2 +
     1      (cos(lat1r) * cos(lat2r) * (sin(dlon/2))**2)
        c = 2 * atan2(sqrt(a), sqrt(1.D0-a))
        d = r_earth(lat1r) * c
      endif
      latlontodistance = d
      return
      end

latlontodistance returns the distance between 2 points in miles, given the input latitude and longitude of 2 points in degrees.