code: function(position1, velocity1, position2, velocity2) {
      var tcpa = this.calcCPATime(position1, velocity1, position2, velocity2);
      if(tcpa === undefined)
        return undefined;
      return this.getPositionByVeloAndTime(position1, velocity1, tcpa);
    }
docs: Calculates the position of closest point of approach (CPA) of track 1.
  @method calcCPAPositionTarget1
  @param position1 {Vector3d} The position of track 1.
  @param velocity1 {Vector3d} The velocity of track 1.
  @param position2 {Vector3d} The position of track 2.
  @param velocity2 {Vector3d} The velocity of track 2.
  @return {Vector3d} The position of CPA or undefined if CPA does not exists.
  @for motionpredict