EDG-TK-FKI

Code:

• David A Cary shares this code:

  On page
  http://techref.massmind.org/techref/piclist/questions.htm
  you ask how to calculate the great-circle distance with a PIC18F452.
  (Microchip says the PIC18F452 is "Not Recommended for new design ... Please consider using device PIC18F4520").
  
  The article
  http://en.wikipedia.org/wiki/Great-circle_distance
  recommends using this formula for small distances:
  
  A = LAT1, B = LONG1
  C = LAT2, D = LONG2
  // (all in radians; multiply angles in degrees by pi/180 to get angles in radians)
  
  // find angular distance S in radians
  T = ( sin( (C-A)/2 ) )^2 + cos(A)*cos(C)*( sin( (D-B)/2 ) )^2;
  S = 2*arcsin( sqrt( T ) );
  // convert angular distance to distance in meters
  // (By definition, Earth has a circumference of 40 Megameters)
  distance = S * (40_000_000 / (2*pi));
  
  So ... What exactly seems to be the problem?
  If you are writing the program from scratch in assembly language,
  or C or BASIC compiler doesn't already include a floating-point or fixed-point trig library, you'll need an implementation of "sqrt()", "sin()", "cos()", and "arcsin()" of "enough" accuracy.
  Oh, and also "*" and "+".
  (This program, like all PIC programs I've written so far, doesn't need a "/" routine -- "/" is in the source code, but it is pre-computed by my desktop machine at compile time).
  
  I suspect all the routines you might need are in the app notes mentioned at
  http://techref.massmind.org/techref/method/math/fixed.htm
  .
  
  Possibly faster and/or smaller code, written after (?) those app notes were published, are listed at
  square root in assembly language:
  /techref/microchip/math/sqrt/
  trig functions in assembly language:
  /techref/microchip/math/index.htm
  
  Do you need more accuracy than those implementations give?
  Is there something we need to fix about the way those functions "fit together" ?
  
  What is the size of the resulting program, compared to the 32 KBytes of program space in the PIC18F4520 ?
  

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