Function DefineAxis

mapgraticule.c:1162–1239

********************************************************************************************************************** * DefineAxes - Copyright (c) 2000, Michael P.D. Bramley. * * Permission is granted to use this code without restriction as long as * this copyright notice appears in all source files. * * Minor tweaks to incrment calculations - jnovak */

 * Minor tweaks to incrment calculations - jnovak
 */
void DefineAxis( int iTickCountTarget, double *Min, double *Max, double *Inc )
{
  /* define local variables... */

  double Test_inc,    /* candidate increment value */
         Test_min,    /* minimum scale value */
         Test_max,    /* maximum scale value */
         Range = *Max - *Min ;  /* range of data */

  int i = 0 ;   /* counter */

  /* don't create problems -- solve them */

  if( Range < 0 )  {
    *Inc = 0 ;
    return ;
  }

  /* handle special case of repeated values */

  else if( Range == 0)  {   
    *Min = ceil(*Max) - 1 ;
    *Max = *Min + 1 ;
    *Inc = 1 ;
    return ;
  }

  /* compute candidate for increment */

  Test_inc = pow( 10.0, ceil( log10( Range/10 ) ) ) ;
  if(*Inc > 0 && ( Test_inc < *Inc || Test_inc > *Inc ))
     Test_inc = *Inc;

   /* establish maximum scale value... */
   Test_max = ( (long)(*Max / Test_inc)) * Test_inc ;

   if( Test_max < *Max )
      Test_max += Test_inc ;

   /* establish minimum scale value... */
   Test_min = Test_max ;
   do {
     ++i ;
     Test_min -= Test_inc ;
   } while( Test_min > *Min ) ;

   /* subtracting small values can screw up the scale limits, */
   /* eg: if DefineAxis is called with (min,max)=(0.01, 0.1), */
   /* then the calculated scale is 1.0408E17 TO 0.05 BY 0.01. */
   /* the following if statment corrects for this... */

   /* if(fabs(Test_min) < 1E-10) */
   /* Test_min = 0 ; */

   /* adjust for too few tick marks */

   if(iTickCountTarget <= 0)
     iTickCountTarget   = MAPGRATICULE_ARC_MINIMUM;