code: public void setVeIncrement(double value)
      {
          if (value < 0)
          {
              String message = Logging.getMessage("generic.ArgumentOutOfRange", value);
              Logging.logger().severe(message);
              throw new IllegalArgumentException(message);
          }
          this.veStep = value;
      }
docs: Set the vertical exaggeration increment. At each iteration the current vertical exaggeration will be increased or
  decreased by this amount. Must be greater than or equal to zero. Default value is 0.1.
  
  @param value the vertical exaggeration increment.
  
  @throws IllegalArgumentException