Algorithms for processing Compass data.

4:39 PM 3/13/98 Dave Wright


To remove "jaggies" from a times series of compass data prior
to plotting, do the following:


  if(input_value>270)     
     bias_value=180;     
  if(180<input_value<270) 
     bias_value=0;
  if(input_value<180)
    {
     plotted_value=input_value+bias_value;
    }
  else
    {
     plotted_value=input_value;
    }

this will cause the output data range to be 0 to 540 degrees,
with the "East" half ot the compass being represented as
either 0 to 180 degrees or 360 to 540 degrees as required
to eliminate the jaggie caused by frequent 359 to 0 transitions
in the raw data.


To determine the difference in two compass values (shortest path):

  if(ABS(plotted_value=first_value-second_value)>180)   */ is answer "long way around"? /*
    {
     if(plotted_value<0)                                */ yes, normalize according to sign /*
       {
        plotted_value+=360;
       }
     else
       {
        plotted_value-=360;
       }
    }


                     END