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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17  package org.apache.commons.geometry.euclidean.threed.rotation;
    18
    19  /** Enum defining the possible reference frames for locating axis
    20   * positions during a rotation sequence.
    21   */
    22  public enum AxisReferenceFrame {
    23
    24      /** Defines a relative reference frame for a rotation sequence. Sequences
    25       * with this type of reference frame are called <em>intrinsic rotations</em>.
    26       *
    27       * <p>
    28       * When using a relative reference frame, each successive axis
    29       * is located relative to the "thing" being rotated and not to some
    30       * external frame of reference. For example, say that a rotation sequence
    31       * is defined around the {@code x}, {@code y}, and {@code z} axes in
    32       * that order. The first rotation will occur around the standard {@code x}
    33       * axis. The second rotation, however, will occur around the {@code y}
    34       * axis after it has been rotated by the first rotation; we can call this
    35       * new axis {@code y'}. Similarly, the third rotation will occur around
    36       * {@code z''}, which may or may not match the original {@code z} axis.
    37       * A good real-world example of this type of situation is an airplane,
    38       * where a pilot makes a sequence of rotations in order, with each rotation
    39       * using the airplane's own up/down, left/right, back/forward directions
    40       * as the frame of reference.
    41       * </p>
    42       */
    43      RELATIVE,
    44
    45      /** Defines an absolute reference frame for a rotation sequence. Sequences
    46       * with this type of reference frame are called <em>extrinsic rotations</em>.
    47       *
    48       * <p>
    49       * In contrast with the relative reference frame, the absolute reference frame
    50       * remains fixed throughout a rotation sequence, with each rotation axis not
    51       * affected by the rotations.
    52       * </p>
    53       */
    54      ABSOLUTE
    55  }