+/*
+ * Copyright 2006 the original author or authors.
+ *
+ * Licensed 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.wamblee.gps.geometry;
+
+import org.wamblee.general.Pair;
+
+/**
+ * Represents a plane. Usually used to represent a tangent plane to the earth surface to
+ * locally approximate the earth as flat.
+ */
+public class Plane {
+
+ private static final double EPS = 1e-4;
+
+ private Coordinates _point;
+ private Coordinates _normal;
+ private Coordinates _north;
+ private Coordinates _east;
+
+ /**
+ * Constructs a plane.
+ * @param aPoint Point on the plane.
+ * @param aNormal Normal, not necessarily normalized.
+ */
+ public Plane(Point aPoint, Point aNormal) {
+ _point = aPoint.getReferenceCoordinates();
+ _normal = aNormal.getReferenceCoordinates().normalize();
+ Coordinates north = new Coordinates(0.0, 0.0, 1.0);
+ _north = north.subtract(_normal.scale(north.innerProduct(_normal))).normalize();
+ _east = _north.outerProduct(_normal);
+
+ if ( _normal.innerProduct(_north) > EPS ) {
+ throw new IllegalArgumentException("North access is not within the plane");
+ }
+ }
+
+ /**
+ * Projects a point onto the plane.
+ * @param aPoint Point to project.
+ * @return Projected point.
+ */
+ private Coordinates project(Point aPoint) {
+ Coordinates ref = aPoint.getReferenceCoordinates();
+ double lambda = _normal.innerProduct(
+ _point.subtract(ref));
+ return ref.add(_normal.scale(lambda));
+ }
+
+ /**
+ * Returns normalized coordinates within the plane of the projection of a point.
+ */
+ public Pair<Double,Double> normalizedProjection(Point aPoint) {
+ Coordinates projection = project(aPoint);
+ Coordinates delta = projection.subtract(_point);
+ double x1 = delta.innerProduct(_north);
+ double x2 = delta.innerProduct(_east);
+ return new Pair<Double,Double>(x1, x2);
+ }
+}