XPost: alt.windows7.general, alt.comp.os.windows-10   
   From: address@is.invalid   
      
   John,   
      
   >> Did you _try_ using just the tangent on a couple of places?   
   ...   
   > I have to do some more experiments.   
      
   After having done so, it looks like that   
      
   tan(DegToRad(Latitude)*0.78)\2.53627   
      
   gives a nice result.   
      
   Though I used 75 degree latitude as the reference for the "will the   
   calculated lines overlap the ones on the image?" test, causing all lower   
   calculations to be /just/ under the lines on the image.   
      
   Re-doing it using 65 degree latitude as a reference should give a better   
   result (75 degree just above its target, the others just below their target)   
      
   As I mentioned before, good enough to get an indication of the location   
   you're looking for, but it can be hundreds of miles to low (or high) ...   
      
   By the way, 0.78 is rather close to Pi/4 .  Somehow that raises my suspicion   
   that that is the actual value to be used, and my 0.78 is caused by my "that   
   looks good" eyeballing ...   
      
   Regards,   
   Rudy Wieser   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)