Re: longitude / latitude distance calculations

[Barbara Morris <bmorris@xxxxxxxxxx>]

Karen Brasier wrote:
> 
> Working on a project and need to know the distance in miles between two
> locations.  The information that I have in the file to use to do this is the
> longitude and latitude.  I have seen the code in PC jargon, but have not
> been able to find anything about how to accomplish this in RPG.    Any
> suggestions would be appreciated... I am cutting/pasting the calc to
> accomplish this below...    as I look at this, I am lost! (or worse, lol)
> surely, there is an easier way, but in searching the archives, I found
> nothing on this...

You can convert this fairly easily to RPG.  You will have to define
prototypes for some math functions in the C runtime library: sin, cose,
acos.  They all have the same pattern:

D sin         pr         8F   extproc('sin')
D   arg                  8F   value

For the deg2rad function, you can define an RPG subprocedure to handle
that.  I'm guessing that "cdbl" just converts to double, and that you
can just define deg2rad like this (similarly for rad2deg).

P deg2rad     b
D deg2rad     pi         8F
D   deg                  8F   value
C       return   deg * pi / 180
P             e

You don't need their acos function since C runtime has it.

Define all the variables as 8F.

Then the calculations are the same.  (I would use the name "temp"
instead of "dist".  I find it icky to call rad2deg with a  parameter
called "dist").

  theta = lon1 - lon2;
  dist = sin(deg2rad(lat1)) * sin(deg2rad(lat2)) + 
        cos(deg2rad(lat1)) * cos(deg2rad(lat2)) * cos(deg2rad(theta));
  dist = acos(dist);
  dist = rad2deg(dist);
  distance = dist * 60 * 1.1515;
  Select;
    When unit = 'k';  // kilometres
      distance = distance * 1.609344;
    When unit = 'n';  // nautical?
      distance = distance * 0.8684;
  Endsl;
  Return distance;

You'll need BNDDIR('QC2LE') in your H spec.

Hope this helps you some.

> 
> const pi = 3.14159265358979323846
> 
> Function distance(lat1, lon1, lat2, lon2, unit)
>   Dim theta, dist
>   theta = lon1 - lon2
>   dist = sin(deg2rad(lat1)) * sin(deg2rad(lat2)) + cos(deg2rad(lat1)) *
> cos(deg2rad(lat2)) * cos(deg2rad(theta))
>   response.write "dist = " & dist & "<br>"
>   dist = acos(dist)
>   dist = rad2deg(dist)
>   response.write "dist = " & dist & "<br>"
>   distance = dist * 60 * 1.1515
>   Select Case ucase(unit)
>     Case "k"
>       distance = distance * 1.609344
>     Case "n"
>       distance = distance * 0.8684
>   End Select
> End Function
> 
> '::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> ':::  this function get the arccos function using arctan function   :::
> '::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> Function acos(rad)
>   If abs(rad) <> 1 Then
>     acos = pi/2 - atn(rad / sqr(1 - rad * rad))
>   ElseIf rad = -1 Then
>     acos = pi
>   End If
> End function
> 
> '::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> ':::  this function converts decimal degrees to radians             :::
> '::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> Function deg2rad(deg)
>         deg2rad = cdbl(deg * pi / 180)
> End Function
> 
> '::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> ':::  this function converts radians to decimal degrees             :::
> '::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> Function rad2deg(rad)
>         rad2deg = cdbl(rad * 180 / pi)
> End Function
> 
> msgbox(distance(32.9697, -96.80322, 29.46786, -98.53506, "m") & "
> miles<br>")
> msgbox(distance(32.9697, -96.80322, 29.46786, -98.53506, "k") & "
> kilometers<br>")
> msgbox(distance(32.9697, -96.80322, 29.46786, -98.53506, "n") & " nautical
> miles<br>")
> 
> Karen Brasier
> I.T. Department - Software Analyst
> Standard Furniture Manufacturing Co.
> Bay Minette, Alabama 36507
> (251) 937-6741 ext 8848
> There are 10 kinds of people in the world, those that understand binary and
> those that do not.
> 
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