code: public String calcDirection(Instruction nextI) {
          double azimuth = calcAzimuth(nextI);
          if (Double.isNaN(azimuth))
              return "";
  
          return AC.azimuth2compassPoint(azimuth);
      }
docs: Return the direction like 'NE' based on the first tracksegment of the instruction. If
  Instruction does not contain enough coordinate points, an empty string will be returned.