code: public void set(Vector3D v1, Vector3D v2, Vector3D v3) {
          this.MODE = TRIANGLE_3D;
          this.x1 = v1.getX();
          this.y1 = v1.getY();
          this.z1 = v1.getZ();
          this.x2 = v2.getX();
          this.y2 = v2.getY();
          this.z1 = v2.getZ();
          this.x3 = v3.getX();
          this.y3 = v3.getY();
          this.z1 = v3.getZ();
          calcG();
      }
docs: Sets x,y-coordinate of corners.
  
  @param v1 The coordinates of the first corner.
  @param v2 The coordinates of the second corner.
  @param v3 The coordinates of the third corner.