From: address@is.invalid   
      
   Paul,   
      
   > ************ CoPilot Answer *************   
   ...   
   > double y = 0.5 - (log(tan(PI/4.0 + rad/2.0)) / (2.0 * PI));   
   ...   
   > Enter Latitude in degrees: 39   
   > Enter Longitude in degrees: -77   
   > Your screen data point is at X=0.286111  Y=0.382179   
      
   :-)  That 0.382179 is 0.06+ larger than what I got from the formule I   
   posted - and that one was already *way* to big.   
      
   It looks like the result needs to be in the neighbourhood of 2.3   
      
   If I leave off the "0.5 -" part (likely a pre-inclusion of "half the images   
   height") than I get 0.118, which is still about half of what it needs to be.   
      
   For a test I put 89 degrees latitude into that CoPilot formule I get a   
   result of *minus* 0.2662 - which should never happen.   
      
   When I again leave out the "0.5 -" part I get a result of 0.766 - which   
   feels way to small.   
      
   I have absolutily no idea what is happening with those formules (I've now   
   tried four of them).   
      
      
   By the way: odd that it has brackets around the "log(...) / (2.0 *PI)" part,   
   as if CoPilot isn't sure about if division comes before subtraction.  Same   
   for the "/ (2.0 * PI)" part.   
      
   Here are the partial results from that CoPilot formule :   
      
   Lat: 39   
   Ang: .680952380952381   
   Tan: 2.09899066938588   
   Log: .741456595562241   
   Div: .117959003839447   
   Res: .382040996160553   
      
   Regards,   
   Rudy Wieser   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)