From: Josselin <josselin@...>
Date: 2007-05-19T00:40:09+09:00
Subject: Re: Math lib (even in C or C++... nobody is perfect !)

On 2007-05-18 15:38:27 +0200, Severin Schoepke 
<severin.schoepke@gmail.com> said:

> Hi!
> 
> Whenever I need to use a math lib in C, I use the GNU Scientific 
> Library (GSL): http://www.gnu.org/software/gsl/
> However, no idea if it contains what you need...
> 
> cheers, Severin
> 
> 
> 
> Josselin schrieb:
>> I am looking for a function to calculate the barycentre of a point list 
>> (GPS coordinates lat/lng) ..
>> 
>> anybody aware of such lib or utility I could rewrite in Ruby ? bet it 
>> doesn't exist yet
>> 
>> thanks for any hint
>> joss

got it from a PHP script..  translated into Ruby...

def deg2rad(d)
    (d/180.0)*Math::PI
end
def rad2deg(r)
    (r/Math::PI)*180
end


def self.gravity_center(placemarks)
  sumx = 0.0
  sumy = 0.0
  sumz = 0.0

  for  placemark in placemarks do
          # convert to radians
          lat = deg2rad(placemark[0])
          lon = deg2rad(placemark[1])
          # convert spherical coordinate into cartesian
          x = Math::cos(lat) * Math::sin(lon)
          y = Math::cos(lat) * Math::cos(lon)
          z = Math::sin(lat)
          # sum the vectors
          sumx += x
          sumy += y
          sumz += z
  end

  # convert cartesian coordinate back to spherical
  meanz = sumz / placemarks.nitems
  lon = rad2deg(Math::atan2(sumx, sumy))

  meanx = sumx / placemarks.nitems
  meany = sumy / placemarks.nitems
  lat = rad2deg(Math::atan(meanz / Math::sqrt(meanx**2 + meany**2)))
  return [lat, lon]
end