Raymond | dee0849 | 2015-04-02 10:43:13 -0700 | [diff] [blame] | 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.math.analysis.interpolation; |
| 18 | |
| 19 | import java.util.ArrayList; |
| 20 | import java.util.HashMap; |
| 21 | import java.util.List; |
| 22 | import java.util.Map; |
| 23 | |
| 24 | import org.apache.commons.math.DimensionMismatchException; |
| 25 | import org.apache.commons.math.analysis.MultivariateRealFunction; |
| 26 | import org.apache.commons.math.exception.NoDataException; |
| 27 | import org.apache.commons.math.linear.ArrayRealVector; |
| 28 | import org.apache.commons.math.linear.RealVector; |
| 29 | import org.apache.commons.math.random.UnitSphereRandomVectorGenerator; |
| 30 | import org.apache.commons.math.util.FastMath; |
| 31 | |
| 32 | /** |
| 33 | * Interpolating function that implements the |
| 34 | * <a href="http://www.dudziak.com/microsphere.php">Microsphere Projection</a>. |
| 35 | * |
| 36 | * @version $Revision: 990655 $ $Date: 2010-08-29 23:49:40 +0200 (dim. 29 août 2010) $ |
| 37 | */ |
| 38 | public class MicrosphereInterpolatingFunction |
| 39 | implements MultivariateRealFunction { |
| 40 | /** |
| 41 | * Space dimension. |
| 42 | */ |
| 43 | private final int dimension; |
| 44 | /** |
| 45 | * Internal accounting data for the interpolation algorithm. |
| 46 | * Each element of the list corresponds to one surface element of |
| 47 | * the microsphere. |
| 48 | */ |
| 49 | private final List<MicrosphereSurfaceElement> microsphere; |
| 50 | /** |
| 51 | * Exponent used in the power law that computes the weights of the |
| 52 | * sample data. |
| 53 | */ |
| 54 | private final double brightnessExponent; |
| 55 | /** |
| 56 | * Sample data. |
| 57 | */ |
| 58 | private final Map<RealVector, Double> samples; |
| 59 | |
| 60 | /** |
| 61 | * Class for storing the accounting data needed to perform the |
| 62 | * microsphere projection. |
| 63 | */ |
| 64 | private static class MicrosphereSurfaceElement { |
| 65 | |
| 66 | /** Normal vector characterizing a surface element. */ |
| 67 | private final RealVector normal; |
| 68 | |
| 69 | /** Illumination received from the brightest sample. */ |
| 70 | private double brightestIllumination; |
| 71 | |
| 72 | /** Brightest sample. */ |
| 73 | private Map.Entry<RealVector, Double> brightestSample; |
| 74 | |
| 75 | /** |
| 76 | * @param n Normal vector characterizing a surface element |
| 77 | * of the microsphere. |
| 78 | */ |
| 79 | MicrosphereSurfaceElement(double[] n) { |
| 80 | normal = new ArrayRealVector(n); |
| 81 | } |
| 82 | |
| 83 | /** |
| 84 | * Return the normal vector. |
| 85 | * @return the normal vector |
| 86 | */ |
| 87 | RealVector normal() { |
| 88 | return normal; |
| 89 | } |
| 90 | |
| 91 | /** |
| 92 | * Reset "illumination" and "sampleIndex". |
| 93 | */ |
| 94 | void reset() { |
| 95 | brightestIllumination = 0; |
| 96 | brightestSample = null; |
| 97 | } |
| 98 | |
| 99 | /** |
| 100 | * Store the illumination and index of the brightest sample. |
| 101 | * @param illuminationFromSample illumination received from sample |
| 102 | * @param sample current sample illuminating the element |
| 103 | */ |
| 104 | void store(final double illuminationFromSample, |
| 105 | final Map.Entry<RealVector, Double> sample) { |
| 106 | if (illuminationFromSample > this.brightestIllumination) { |
| 107 | this.brightestIllumination = illuminationFromSample; |
| 108 | this.brightestSample = sample; |
| 109 | } |
| 110 | } |
| 111 | |
| 112 | /** |
| 113 | * Get the illumination of the element. |
| 114 | * @return the illumination. |
| 115 | */ |
| 116 | double illumination() { |
| 117 | return brightestIllumination; |
| 118 | } |
| 119 | |
| 120 | /** |
| 121 | * Get the sample illuminating the element the most. |
| 122 | * @return the sample. |
| 123 | */ |
| 124 | Map.Entry<RealVector, Double> sample() { |
| 125 | return brightestSample; |
| 126 | } |
| 127 | } |
| 128 | |
| 129 | /** |
| 130 | * @param xval the arguments for the interpolation points. |
| 131 | * {@code xval[i][0]} is the first component of interpolation point |
| 132 | * {@code i}, {@code xval[i][1]} is the second component, and so on |
| 133 | * until {@code xval[i][d-1]}, the last component of that interpolation |
| 134 | * point (where {@code dimension} is thus the dimension of the sampled |
| 135 | * space). |
| 136 | * @param yval the values for the interpolation points |
| 137 | * @param brightnessExponent Brightness dimming factor. |
| 138 | * @param microsphereElements Number of surface elements of the |
| 139 | * microsphere. |
| 140 | * @param rand Unit vector generator for creating the microsphere. |
| 141 | * @throws DimensionMismatchException if the lengths of {@code yval} and |
| 142 | * {@code xval} (equal to {@code n}, the number of interpolation points) |
| 143 | * do not match, or the the arrays {@code xval[0]} ... {@code xval[n]}, |
| 144 | * have lengths different from {@code dimension}. |
| 145 | * @throws NoDataException if there are no data (xval null or zero length) |
| 146 | */ |
| 147 | public MicrosphereInterpolatingFunction(double[][] xval, |
| 148 | double[] yval, |
| 149 | int brightnessExponent, |
| 150 | int microsphereElements, |
| 151 | UnitSphereRandomVectorGenerator rand) |
| 152 | throws DimensionMismatchException, NoDataException { |
| 153 | if (xval.length == 0 || xval[0] == null) { |
| 154 | throw new NoDataException(); |
| 155 | } |
| 156 | |
| 157 | if (xval.length != yval.length) { |
| 158 | throw new DimensionMismatchException(xval.length, yval.length); |
| 159 | } |
| 160 | |
| 161 | dimension = xval[0].length; |
| 162 | this.brightnessExponent = brightnessExponent; |
| 163 | |
| 164 | // Copy data samples. |
| 165 | samples = new HashMap<RealVector, Double>(yval.length); |
| 166 | for (int i = 0; i < xval.length; ++i) { |
| 167 | final double[] xvalI = xval[i]; |
| 168 | if ( xvalI.length != dimension) { |
| 169 | throw new DimensionMismatchException(xvalI.length, dimension); |
| 170 | } |
| 171 | |
| 172 | samples.put(new ArrayRealVector(xvalI), yval[i]); |
| 173 | } |
| 174 | |
| 175 | microsphere = new ArrayList<MicrosphereSurfaceElement>(microsphereElements); |
| 176 | // Generate the microsphere, assuming that a fairly large number of |
| 177 | // randomly generated normals will represent a sphere. |
| 178 | for (int i = 0; i < microsphereElements; i++) { |
| 179 | microsphere.add(new MicrosphereSurfaceElement(rand.nextVector())); |
| 180 | } |
| 181 | |
| 182 | } |
| 183 | |
| 184 | /** |
| 185 | * @param point Interpolation point. |
| 186 | * @return the interpolated value. |
| 187 | */ |
| 188 | public double value(double[] point) { |
| 189 | |
| 190 | final RealVector p = new ArrayRealVector(point); |
| 191 | |
| 192 | // Reset. |
| 193 | for (MicrosphereSurfaceElement md : microsphere) { |
| 194 | md.reset(); |
| 195 | } |
| 196 | |
| 197 | // Compute contribution of each sample points to the microsphere elements illumination |
| 198 | for (Map.Entry<RealVector, Double> sd : samples.entrySet()) { |
| 199 | |
| 200 | // Vector between interpolation point and current sample point. |
| 201 | final RealVector diff = sd.getKey().subtract(p); |
| 202 | final double diffNorm = diff.getNorm(); |
| 203 | |
| 204 | if (FastMath.abs(diffNorm) < FastMath.ulp(1d)) { |
| 205 | // No need to interpolate, as the interpolation point is |
| 206 | // actually (very close to) one of the sampled points. |
| 207 | return sd.getValue(); |
| 208 | } |
| 209 | |
| 210 | for (MicrosphereSurfaceElement md : microsphere) { |
| 211 | final double w = FastMath.pow(diffNorm, -brightnessExponent); |
| 212 | md.store(cosAngle(diff, md.normal()) * w, sd); |
| 213 | } |
| 214 | |
| 215 | } |
| 216 | |
| 217 | // Interpolation calculation. |
| 218 | double value = 0; |
| 219 | double totalWeight = 0; |
| 220 | for (MicrosphereSurfaceElement md : microsphere) { |
| 221 | final double iV = md.illumination(); |
| 222 | final Map.Entry<RealVector, Double> sd = md.sample(); |
| 223 | if (sd != null) { |
| 224 | value += iV * sd.getValue(); |
| 225 | totalWeight += iV; |
| 226 | } |
| 227 | } |
| 228 | |
| 229 | return value / totalWeight; |
| 230 | |
| 231 | } |
| 232 | |
| 233 | /** |
| 234 | * Compute the cosine of the angle between 2 vectors. |
| 235 | * |
| 236 | * @param v Vector. |
| 237 | * @param w Vector. |
| 238 | * @return cosine of the angle |
| 239 | */ |
| 240 | private double cosAngle(final RealVector v, final RealVector w) { |
| 241 | return v.dotProduct(w) / (v.getNorm() * w.getNorm()); |
| 242 | } |
| 243 | |
| 244 | } |