;*********************************************
;  Calculate the distance in meters from two points on the earth
;
;  Point 1
;  lat1 = latitude of point 1
;  lon1 = longitude of point 1
;
;  Point(s) 2
;  lat2 = latitude of point 2 OR array
;  lon2 = longitude of point 2 OR array
;
;  Returned value
;  dm = distance in meters
;*********************************************

pro haversine_distance,lat1,lon1,lat2,lon2,dm

;  Convert from degrees to radians
rlat1=double(lat1*(!dpi/180.0)) 
rlon1=double(lon1*(!dpi/180.0))
rlat2=double(lat2*(!dpi/180.0)) 
rlon2=double(lon2*(!dpi/180.0)) 

;  Calculate these differences
drlat=rlat2-rlat1
drlon=rlon2-rlon1

;  Earth radius - km converted to meters
re=double(6378.0*1000.0)

;  Haversine formula for small distances - most accurate
;  dm = distance in meters
a=(sin(drlat/2))^2 + cos(rlat1) *cos(rlat2)*(sin(drlon/2))^2
c=2*atan(sqrt(a),sqrt(1-a))
dm=re*c

return
end