Normalize Angle (from https://github.com/apache/commons-math/blob/53ec46ba272e23c0c96ada42f26f4e70e96f3115/src/main/java/org/apache/commons/math4/util/MathUtils.java#L107 )

MathUtils.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.
 */

public final class MathUtils {
   /**
     * Normalize an angle in a 2π wide interval around a center value.
     * <p>This method has three main uses:</p>
     * <ul>
     *   <li>normalize an angle between 0 and 2&pi;:<br>
     *       {@code a = MathUtils.normalizeAngle(a, FastMath.PI);}</li>
     *   <li>normalize an angle between -&pi; and +&pi;<br>
     *       {@code a = MathUtils.normalizeAngle(a, 0.0);}</li>
     *   <li>compute the angle between two defining angular positions:<br>
     *       {@code angle = MathUtils.normalizeAngle(end, start) - start;}</li>
     * </ul>
     * <p>Note that due to numerical accuracy and since &pi; cannot be represented
     * exactly, the result interval is <em>closed</em>, it cannot be half-closed
     * as would be more satisfactory in a purely mathematical view.</p>
     * @param a angle to normalize
     * @param center center of the desired 2&pi; interval for the result
     * @return a-2k&pi; with integer k and center-&pi; &lt;= a-2k&pi; &lt;= center+&pi;
     * @since 1.2
     */
     public static double normalizeAngle(double a, double center) {
       double r = Math.toRadians(lon);
       double norm_r = r - (2 * Math.PI) * Math.floor((r + Math.PI - Math.toRadians(center)) / (2 * Math.PI));

       return Math.toDegrees(norm_r);
     }
 }