/*
* 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.math4.analysis.interpolation;
import org.apache.commons.math4.analysis.MultivariateFunction;
import org.apache.commons.math4.util.FastMath;
import org.junit.Assert;
import org.junit.Test;
/**
* Test case for the {@link MicrosphereProjectionInterpolator
* "microsphere projection"} interpolator.
*/
public final class MicrosphereProjectionInterpolatorTest {
/**
* Test of interpolator for a plane.
* <p>
* y = 2 x<sub>1</sub> - 3 x<sub>2</sub> + 5
*/
@Test
public void testLinearFunction2D() {
MultivariateFunction f = new MultivariateFunction() {
@Override
public double value(double[] x) {
if (x.length != 2) {
throw new IllegalArgumentException();
}
return 2 * x[0] - 3 * x[1] + 5;
}
};
final double darkFraction = 0.5;
final double darkThreshold = 1e-2;
final double background = Double.NaN;
final double exponent = 1.1;
final boolean shareSphere = true;
final double noInterpolationTolerance = Math.ulp(1d);
// N-dimensional interpolator.
final MultivariateInterpolator interpolator
= new MicrosphereProjectionInterpolator(2, 500,
darkFraction,
darkThreshold,
background,
exponent,
shareSphere,
noInterpolationTolerance);
// 2D interpolator.
final MultivariateInterpolator interpolator2D
= new MicrosphereProjectionInterpolator(new InterpolatingMicrosphere2D(16,
darkFraction,
darkThreshold,
background),
exponent,
shareSphere,
noInterpolationTolerance);
final double min = -1;
final double max = 1;
final double range = max - min;
final int res = 5;
final int n = res * res; // Number of sample points.
final int dim = 2;
double[][] x = new double[n][dim];
double[] y = new double[n];
int index = 0;
for (int i = 0; i < res; i++) {
final double x1Val = toCoordinate(min, range, res, i);
for (int j = 0; j < res; j++) {
final double x2Val = toCoordinate(min, range, res, j);
x[index][0] = x1Val;
x[index][1] = x2Val;
y[index] = f.value(x[index]);
++index;
}
}
final MultivariateFunction p = interpolator.interpolate(x, y);
final MultivariateFunction p2D = interpolator2D.interpolate(x, y);
double[] c = new double[dim];
double expected, result, result2D;
final int sampleIndex = 2;
c[0] = x[sampleIndex][0];
c[1] = x[sampleIndex][1];
expected = f.value(c);
result = p.value(c);
result2D = p2D.value(c);
Assert.assertEquals("on sample point (exact)", expected, result2D, FastMath.ulp(1d));
Assert.assertEquals("on sample point (ND vs 2D)", result2D, result, FastMath.ulp(1d));
// Interpolation.
c[0] = 0.654321;
c[1] = -0.345678;
expected = f.value(c);
result = p.value(c);
result2D = p2D.value(c);
Assert.assertEquals("interpolation (exact)", expected, result2D, 1e-1);
Assert.assertEquals("interpolation (ND vs 2D)", result2D, result, 1e-1);
// Extrapolation.
c[0] = 0 - 1e-2;
c[1] = 1 + 1e-2;
expected = f.value(c);
result = p.value(c);
result2D = p2D.value(c);
Assert.assertFalse(Double.isNaN(result));
Assert.assertFalse(Double.isNaN(result2D));
Assert.assertEquals("extrapolation (exact)", expected, result2D, 1e-1);
Assert.assertEquals("extrapolation (ND vs 2D)", result2D, result, 1e-2);
// Far away.
c[0] = 20;
c[1] = -30;
result = p.value(c);
Assert.assertTrue(result + " should be NaN", Double.isNaN(result));
result2D = p2D.value(c);
Assert.assertTrue(result2D + " should be NaN", Double.isNaN(result2D));
}
/**
* @param min Minimum of the coordinate range.
* @param range Extent of the coordinate interval.
* @param res Number of pixels.
* @param pixel Pixel index.
*/
private static double toCoordinate(double min,
double range,
int res,
int pixel) {
return pixel * range / (res - 1) + min;
}
}