commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/AbstractAffineTransformMatrix.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.geometry.euclidean;

import org.apache.commons.geometry.euclidean.internal.Vectors;

/** Base class for affine transform matrices in Euclidean space.
 *
 * @param <V> Vector/point implementation type defining the space.
 */
public abstract class AbstractAffineTransformMatrix<V extends EuclideanVector<V>>
    implements EuclideanTransform<V> {

    /** Apply this transform to the given vector, ignoring translations and normalizing the
     * result. This is equivalent to {@code transform.applyVector(vec).normalize()} but without
     * the intermediate vector instance.
     *
     * @param vec the vector to transform
     * @return the new, transformed unit vector
     * @throws IllegalArgumentException if the transformed vector coordinates cannot be normalized
     * @see #applyVector(EuclideanVector)
     */
    public abstract V applyDirection(V vec);

    /** Get the determinant of the matrix.
     * @return the determinant of the matrix
     */
    public abstract double determinant();

    /** {@inheritDoc}
     *
     * <p>This method returns true if the determinant of the matrix is positive.</p>
     */
    @Override
    public boolean preservesOrientation() {
        return determinant() > 0.0;
    }

    /** Get the determinant of the instance for use in calculating the matrix
     * inverse. An {@link IllegalStateException} is thrown if the determinant is
     * NaN, infinite, or zero.
     * @return the determinant of the matrix
     * @throws IllegalStateException if the matrix determinant value is NaN, infinite,
     *      or zero
     */
    protected double getDeterminantForInverse() {
        final double det = determinant();
        if (!Vectors.isRealNonZero(det)) {
            nonInvertibleTransform("matrix determinant is " + det);
        }
        return det;
    }

    /** Check that the given matrix element is valid for use in calculation of
     * a matrix inverse, throwing an {@link IllegalStateException} if not.
     * @param element matrix entry to check
     * @throws IllegalStateException if the element is not valid for use
     *      in calculating a matrix inverse, ie if it is NaN or infinite.
     */
    protected void validateElementForInverse(final double element) {
        if (!Double.isFinite(element)) {
            nonInvertibleTransform("invalid matrix element: " + element);
        }
    }

    /** Create an exception indicating that a transform matrix is not able
     * to be inverted.
     * @param msg message containing specific information for the failure
     * @return an exception indicating that a transform matrix is not able
     *      to be inverted
     */

    /** Throw an exception indicating that the instance is not able to be inverted.
     * @param msg message containing the specific reason that the matrix cannot
     *      be inverted
     * @throws IllegalStateException containing the given error message
     */
    protected void nonInvertibleTransform(final String msg) {
        throw new IllegalStateException("Transform is not invertible; " + msg);
    }
}