View Javadoc

    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;
    18
    19  import java.util.Objects;
    20
    21  import org.apache.commons.geometry.core.Transform;
    22  import org.apache.commons.geometry.core.partitioning.AbstractHyperplane;
    23  import org.apache.commons.geometry.core.partitioning.Hyperplane;
    24  import org.apache.commons.geometry.core.precision.DoublePrecisionContext;
    25  import org.apache.commons.geometry.euclidean.threed.line.Line3D;
    26  import org.apache.commons.geometry.euclidean.threed.line.Lines3D;
    27  import org.apache.commons.geometry.euclidean.threed.rotation.QuaternionRotation;
    28  import org.apache.commons.geometry.euclidean.twod.ConvexArea;
    29
    30  /** Class representing a plane in 3 dimensional Euclidean space. Each plane is defined by a
    31   * {@link #getNormal() normal} and an {@link #getOriginOffset() origin offset}. If \(\vec{n}\) is the plane normal,
    32   * \(d\) is the origin offset, and \(p\) and \(q\) are any points in the plane, then the following are true:
    33   * <ul>
    34   *  <li>\(\lVert \vec{n} \rVert\) = 1</li>
    35   *  <li>\(\vec{n} \cdot (p - q) = 0\)</li>
    36   *  <li>\(d = - (\vec{n} \cdot q)\)</li>
    37   *  </ul>
    38   *  In other words, the normal is a unit vector such that the dot product of the normal and the difference of
    39   *  any two points in the plane is always equal to \(0\). Similarly, the {@code origin offset} is equal to the
    40   *  negation of the dot product of the normal and any point in the plane. The projection of the origin onto the
    41   *  plane (given by {@link #getOrigin()}), is computed as \(-d \vec{n}\).
    42   *
    43   * <p>Instances of this class are guaranteed to be immutable.</p>
    44   * @see Planes
    45   */
    46  public class Plane extends AbstractHyperplane<Vector3D> {
    47
    48      /** Plane normal. */
    49      private final Vector3D.Unit normal;
    50
    51      /** Offset of the origin with respect to the plane. */
    52      private final double originOffset;
    53
    54      /** Construct a plane from its component parts.
    55       * @param normal unit normal vector
    56       * @param originOffset offset of the origin with respect to the plane
    57       * @param precision precision context used to compare floating point values
    58       */
    59      Plane(final Vector3D.Unit normal, final double originOffset,
    60            final DoublePrecisionContext precision) {
    61
    62          super(precision);
    63
    64          this.normal = normal;
    65          this.originOffset = originOffset;
    66      }
    67
    68      /** Get the orthogonal projection of the 3D-space origin in the plane.
    69       * @return the origin point of the plane frame (point closest to the 3D-space
    70       *         origin)
    71       */
    72      public Vector3D getOrigin() {
    73          return normal.multiply(-originOffset);
    74      }
    75
    76      /** Get the offset of the spatial origin ({@code 0, 0, 0}) with respect to the plane.
    77       * @return the offset of the origin with respect to the plane.
    78       */
    79      public double getOriginOffset() {
    80          return originOffset;
    81      }
    82
    83      /** Get the plane normal vector.
    84       * @return plane normal vector
    85       */
    86      public Vector3D.Unit getNormal() {
    87          return normal;
    88      }
    89
    90      /** Return an {@link EmbeddingPlane} instance suitable for embedding 2D geometric objects
    91       * into this plane. Returned instances are guaranteed to be equal between invocations.
    92       * @return a plane instance suitable for embedding 2D subspaces
    93       */
    94      public EmbeddingPlane getEmbedding() {
    95          final Vector3D.Unit u = normal.orthogonal();
    96          final Vector3D.Unit v = normal.cross(u).normalize();
    97
    98          return new EmbeddingPlane(u, v, normal, originOffset, getPrecision());
    99      }
    100
    101     /** {@inheritDoc} */
    102     @Override
    103     public double offset(final Vector3D point) {
    104         return point.dot(normal) + originOffset;
    105     }
    106
    107     /** Get the offset (oriented distance) of the given line with respect to the plane. The value
    108      * closest to zero is returned, which will always be zero if the line is not parallel to the plane.
    109      * @param line line to calculate the offset of
    110      * @return the offset of the line with respect to the plane or 0.0 if the line
    111      *      is not parallel to the plane.
    112      */
    113     public double offset(final Line3D line) {
    114         if (!isParallel(line)) {
    115             return 0.0;
    116         }
    117         return offset(line.getOrigin());
    118     }
    119
    120     /** Get the offset (oriented distance) of the given plane with respect to this instance. The value
    121      * closest to zero is returned, which will always be zero if the planes are not parallel.
    122      * @param plane plane to calculate the offset of
    123      * @return the offset of the plane with respect to this instance or 0.0 if the planes
    124      *      are not parallel.
    125      */
    126     public double offset(final Plane plane) {
    127         if (!isParallel(plane)) {
    128             return 0.0;
    129         }
    130         return originOffset + (similarOrientation(plane) ? -plane.originOffset : plane.originOffset);
    131     }
    132
    133     /** Check if the instance contains a point.
    134      * @param p point to check
    135      * @return true if p belongs to the plane
    136      */
    137     @Override
    138     public boolean contains(final Vector3D p) {
    139         return getPrecision().eqZero(offset(p));
    140     }
    141
    142     /** Check if the instance contains a line.
    143      * @param line line to check
    144      * @return true if line is contained in this plane
    145      */
    146     public boolean contains(final Line3D line) {
    147         return isParallel(line) && contains(line.getOrigin());
    148     }
    149
    150     /** Check if the instance contains another plane. Planes are considered similar if they contain
    151      * the same points. This does not mean they are equal since they can have opposite normals.
    152      * @param plane plane to which the instance is compared
    153      * @return true if the planes are similar
    154      */
    155     public boolean contains(final Plane plane) {
    156         final double angle = normal.angle(plane.normal);
    157         final DoublePrecisionContext precision = getPrecision();
    158
    159         return ((precision.eqZero(angle)) && precision.eq(originOffset, plane.originOffset)) ||
    160                 ((precision.eq(angle, Math.PI)) && precision.eq(originOffset, -plane.originOffset));
    161     }
    162
    163     /** {@inheritDoc} */
    164     @Override
    165     public Vector3D project(final Vector3D point) {
    166         return getOrigin().add(point.reject(normal));
    167     }
    168
    169     /** Project a 3D line onto the plane.
    170      * @param line the line to project
    171      * @return the projection of the given line onto the plane.
    172      */
    173     public Line3D project(final Line3D line) {
    174         final Vector3D direction = line.getDirection();
    175         final Vector3D projection = normal.multiply(direction.dot(normal) * (1 / normal.normSq()));
    176
    177         final Vector3D projectedLineDirection = direction.subtract(projection);
    178         final Vector3D p1 = project(line.getOrigin());
    179         final Vector3D p2 = p1.add(projectedLineDirection);
    180
    181         return Lines3D.fromPoints(p1, p2, getPrecision());
    182     }
    183
    184     /** {@inheritDoc} */
    185     @Override
    186     public PlaneConvexSubset span() {
    187         return Planes.subsetFromConvexArea(getEmbedding(), ConvexArea.full());
    188     }
    189
    190     /** Check if the line is parallel to the instance.
    191      * @param line line to check.
    192      * @return true if the line is parallel to the instance, false otherwise.
    193      */
    194     public boolean isParallel(final Line3D line) {
    195         final double dot = normal.dot(line.getDirection());
    196
    197         return getPrecision().eqZero(dot);
    198     }
    199
    200     /** Check if the plane is parallel to the instance.
    201      * @param plane plane to check.
    202      * @return true if the plane is parallel to the instance, false otherwise.
    203      */
    204     public boolean isParallel(final Plane plane) {
    205         return getPrecision().eqZero(normal.cross(plane.normal).norm());
    206     }
    207
    208     /** {@inheritDoc} */
    209     @Override
    210     public boolean similarOrientation(final Hyperplane<Vector3D> other) {
    211         return (((Plane) other).normal).dot(normal) > 0;
    212     }
    213
    214     /** Get the intersection of a line with this plane.
    215      * @param line line intersecting the instance
    216      * @return intersection point between between the line and the instance (null if
    217      *         the line is parallel to the instance)
    218      */
    219     public Vector3D intersection(final Line3D line) {
    220         final Vector3D direction = line.getDirection();
    221         final double dot = normal.dot(direction);
    222
    223         if (getPrecision().eqZero(dot)) {
    224             return null;
    225         }
    226
    227         final Vector3D point = line.pointAt(0);
    228         final double k = -(originOffset + normal.dot(point)) / dot;
    229
    230         return Vector3D.linearCombination(
    231                 1.0, point,
    232                 k, direction);
    233     }
    234
    235     /** Get the line formed by the intersection of this instance with the given plane.
    236      * The returned line lies in both planes and points in the direction of
    237      * the cross product <code>n<sub>1</sub> x n<sub>2</sub></code>, where <code>n<sub>1</sub></code>
    238      * is the normal of the current instance and <code>n<sub>2</sub></code> is the normal
    239      * of the argument.
    240      *
    241      * <p>Null is returned if the planes are parallel.</p>
    242      *
    243      * @param other other plane
    244      * @return line at the intersection of the instance and the other plane, or null
    245      *      if no such line exists
    246      */
    247     public Line3D intersection(final Plane other) {
    248         final Vector3D direction = normal.cross(other.normal);
    249
    250         if (getPrecision().eqZero(direction.norm())) {
    251             return null;
    252         }
    253
    254         final Vector3D point = intersection(this, other, Planes.fromNormal(direction, getPrecision()));
    255
    256         return Lines3D.fromPointAndDirection(point, direction, getPrecision());
    257     }
    258
    259     /** Build a new reversed version of this plane, with opposite orientation.
    260      * @return a new reversed plane
    261      */
    262     @Override
    263     public Plane reverse() {
    264         return new Plane(normal.negate(), -originOffset, getPrecision());
    265     }
    266
    267     /** {@inheritDoc}
    268      *
    269      * <p>Instances are transformed by selecting 3 representative points from the
    270      * plane, transforming them, and constructing a new plane from the transformed points.
    271      * Since the normal is not transformed directly, but rather is constructed new from the
    272      * transformed points, the relative orientations of points in the plane are preserved,
    273      * even for transforms that do not
    274      * {@link Transform#preservesOrientation() preserve orientation}. The example below shows
    275      * a plane being transformed by a non-orientation-preserving transform. The normal of the
    276      * transformed plane retains its counterclockwise relationship to the points in the plane,
    277      * in contrast with the normal that is transformed directly by the transform.
    278      * </p>
    279      * <pre>
    280      * // construct a plane from 3 points; the normal will be selected such that the
    281      * // points are ordered counterclockwise when looking down the plane normal.
    282      * Vector3D p1 = Vector3D.of(0, 0, 0);
    283      * Vector3D p2 = Vector3D.of(+1, 0, 0);
    284      * Vector3D p3 = Vector3D.of(0, +1, 0);
    285      *
    286      * Plane plane = Planes.fromPoints(p1, p2, p3, precision); // normal is (0, 0, +1)
    287      *
    288      * // create a transform that negates all x-values; this transform does not
    289      * // preserve orientation, i.e. it will convert a right-handed system into a left-handed
    290      * // system and vice versa
    291      * AffineTransformMatrix3D transform = AffineTransformMatrix3D.createScale(-1, 1,  1);
    292      *
    293      * // transform the plane
    294      * Plane transformedPlane = plane.transform(transform);
    295      *
    296      * // the plane normal is oriented such that transformed points are still ordered
    297      * // counterclockwise when looking down the plane normal; since the point (1, 0, 0) has
    298      * // now become (-1, 0, 0), the normal has flipped to (0, 0, -1)
    299      * transformedPlane.getNormal();
    300      *
    301      * // directly transform the original plane normal; the normal is unchanged by the transform
    302      * // since the target space of the transform is left-handed
    303      * AffineTransformMatrix3D normalTransform = transform.normalTransform();
    304      * Vector3D directlyTransformedNormal = normalTransform.apply(plane.getNormal()); // (0, 0, +1)
    305      * </pre>
    306      */
    307     @Override
    308     public Plane transform(final Transform<Vector3D> transform) {
    309         // create 3 representation points lying on the plane, transform them,
    310         // and use the transformed points to create a new plane
    311
    312         final Vector3D u = normal.orthogonal();
    313         final Vector3D v = normal.cross(u);
    314
    315         final Vector3D p1 = getOrigin();
    316         final Vector3D p2 = p1.add(u);
    317         final Vector3D p3 = p1.add(v);
    318
    319         final Vector3D t1 = transform.apply(p1);
    320         final Vector3D t2 = transform.apply(p2);
    321         final Vector3D t3 = transform.apply(p3);
    322
    323         return Planes.fromPoints(t1, t2, t3, getPrecision());
    324     }
    325
    326     /** Translate the plane by the specified amount.
    327      * @param translation translation to apply
    328      * @return a new plane
    329      */
    330     public Plane translate(final Vector3D translation) {
    331         final Vector3D tOrigin = getOrigin().add(translation);
    332
    333         return Planes.fromPointAndNormal(tOrigin, normal, getPrecision());
    334     }
    335
    336     /** Rotate the plane around the specified point.
    337      * @param center rotation center
    338      * @param rotation 3-dimensional rotation
    339      * @return a new plane
    340      */
    341     public Plane rotate(final Vector3D center, final QuaternionRotation rotation) {
    342         final Vector3D delta = getOrigin().subtract(center);
    343         final Vector3D tOrigin = center.add(rotation.apply(delta));
    344
    345         // we can directly apply the rotation to the normal since it will transform
    346         // it properly (there is no translation or scaling involved)
    347         final Vector3D.Unit tNormal = rotation.apply(normal).normalize();
    348
    349         return Planes.fromPointAndNormal(tOrigin, tNormal, getPrecision());
    350     }
    351
    352     /** Return true if this instance should be considered equivalent to the argument, using the
    353      * given precision context for comparison. Instances are considered equivalent if they contain
    354      * the same points, which is determined by comparing the plane {@code origins} and {@code normals}.
    355      * @param other the point to compare with
    356      * @param precision precision context to use for the comparison
    357      * @return true if this instance should be considered equivalent to the argument
    358      * @see Vector3D#eq(Vector3D, DoublePrecisionContext)
    359      */
    360     public boolean eq(final Plane other, final DoublePrecisionContext precision) {
    361         return getOrigin().eq(other.getOrigin(), precision) &&
    362                 normal.eq(other.normal, precision);
    363     }
    364
    365     /** {@inheritDoc} */
    366     @Override
    367     public int hashCode() {
    368         return Objects.hash(normal, originOffset, getPrecision());
    369     }
    370
    371     /** {@inheritDoc} */
    372     @Override
    373     public boolean equals(final Object obj) {
    374         if (this == obj) {
    375             return true;
    376         } else if (obj == null || obj.getClass() != this.getClass()) {
    377             return false;
    378         }
    379
    380         final Plane other = (Plane) obj;
    381
    382         return Objects.equals(this.normal, other.normal) &&
    383                 Double.compare(this.originOffset, other.originOffset) == 0 &&
    384                 Objects.equals(this.getPrecision(), other.getPrecision());
    385     }
    386
    387     /** {@inheritDoc} */
    388     @Override
    389     public String toString() {
    390         final StringBuilder sb = new StringBuilder();
    391         sb.append(getClass().getSimpleName())
    392             .append("[origin= ")
    393             .append(getOrigin())
    394             .append(", normal= ")
    395             .append(normal)
    396             .append(']');
    397
    398         return sb.toString();
    399     }
    400
    401     /** Get the intersection point of three planes. Returns null if no unique intersection point
    402      * exists (ie, there are no intersection points or an infinite number).
    403      * @param plane1 first plane1
    404      * @param plane2 second plane2
    405      * @param plane3 third plane2
    406      * @return intersection point of the three planes or null if no unique intersection point exists
    407      */
    408     public static Vector3D intersection(final Plane plane1, final Plane plane2, final Plane plane3) {
    409
    410         // coefficients of the three planes linear equations
    411         final double a1 = plane1.normal.getX();
    412         final double b1 = plane1.normal.getY();
    413         final double c1 = plane1.normal.getZ();
    414         final double d1 = plane1.originOffset;
    415
    416         final double a2 = plane2.normal.getX();
    417         final double b2 = plane2.normal.getY();
    418         final double c2 = plane2.normal.getZ();
    419         final double d2 = plane2.originOffset;
    420
    421         final double a3 = plane3.normal.getX();
    422         final double b3 = plane3.normal.getY();
    423         final double c3 = plane3.normal.getZ();
    424         final double d3 = plane3.originOffset;
    425
    426         // direct Cramer resolution of the linear system
    427         // (this is still feasible for a 3x3 system)
    428         final double a23 = (b2 * c3) - (b3 * c2);
    429         final double b23 = (c2 * a3) - (c3 * a2);
    430         final double c23 = (a2 * b3) - (a3 * b2);
    431         final double determinant = (a1 * a23) + (b1 * b23) + (c1 * c23);
    432
    433         // use the precision context of the first plane to determine equality
    434         if (plane1.getPrecision().eqZero(determinant)) {
    435             return null;
    436         }
    437
    438         final double r = 1.0 / determinant;
    439         return Vector3D.of((-a23 * d1 - (c1 * b3 - c3 * b1) * d2 - (c2 * b1 - c1 * b2) * d3) * r,
    440                 (-b23 * d1 - (c3 * a1 - c1 * a3) * d2 - (c1 * a2 - c2 * a1) * d3) * r,
    441                 (-c23 * d1 - (b1 * a3 - b3 * a1) * d2 - (b2 * a1 - b1 * a2) * d3) * r);
    442     }
    443 }