feat: add RadialKDTreeInterpolatorFactory (#360)

feat: add RadialKDTreeInterpolatorFactory and RadialKDTreeInterpolator

---------

Co-authored-by: Stephan Saalfeld <saalfelds@janelia.hhmi.org>

src/main/java/net/imglib2/interpolation/neighborsearch/RadialKDTreeInterpolator.java

@@ -0,0 +1,85 @@
+package net.imglib2.interpolation.neighborsearch;
+
+import java.util.function.DoubleUnaryOperator;
+
+import net.imglib2.KDTree;
+import net.imglib2.RealPoint;
+import net.imglib2.RealRandomAccess;
+import net.imglib2.neighborsearch.RadiusNeighborSearch;
+import net.imglib2.neighborsearch.RadiusNeighborSearchOnKDTree;
+import net.imglib2.type.numeric.NumericType;
+
+/**
+ * A {@link RealRandomAccess} for {@link KDTree}s using a radial function used
+ * by {@link RadialKDTreeInterpolatorFactory}.
+ */
+public class RadialKDTreeInterpolator< T extends NumericType< T > > extends RealPoint implements RealRandomAccess< T >
+{
+	protected static final double minThreshold = Double.MIN_VALUE * 1000;
+
+	protected final RadiusNeighborSearch< T > search;
+
+	protected final double maxRadius;
+
+	protected final double maxSquaredRadius;
+
+	protected final KDTree< T > tree;
+
+	protected final T value;
+
+	protected final T tmp;
+
+	protected final DoubleUnaryOperator squaredRadiusFunction;
+
+	public RadialKDTreeInterpolator(
+			final KDTree< T > tree,
+			final DoubleUnaryOperator squaredRadiusFunction,
+			final double maxRadius,
+			final T t )
+	{
+		super( tree.numDimensions() );
+
+		this.squaredRadiusFunction = squaredRadiusFunction;
+		this.tree = tree;
+		this.search = new RadiusNeighborSearchOnKDTree< T >( tree );
+		this.maxRadius = maxRadius;
+		this.maxSquaredRadius = maxRadius * maxRadius;
+		this.value = t.copy();
+		this.tmp = t.copy();
+	}
+
+	public double getMaxRadius()
+	{
+		return maxRadius;
+	}
+
+	@Override
+	public T get()
+	{
+		value.setZero();
+		search.search( this, maxRadius, false );
+		if ( search.numNeighbors() == 0 )
+			return value;
+
+		for ( int i = 0; i < search.numNeighbors(); ++i )
+		{
+			// can't multiply the value returned
+			tmp.set( search.getSampler( i ).get() );
+			tmp.mul( squaredRadiusFunction.applyAsDouble( search.getSquareDistance( i ) ) );
+			value.add( tmp );
+		}
+		return value;
+	}
+
+	@Override
+	public RadialKDTreeInterpolator< T > copy()
+	{
+		return new RadialKDTreeInterpolator< T >( tree, squaredRadiusFunction, maxRadius, value );
+	}
+
+	@Override
+	public RadialKDTreeInterpolator< T > copyRealRandomAccess()
+	{
+		return copy();
+	}
+}

src/main/java/net/imglib2/interpolation/neighborsearch/RadialKDTreeInterpolatorFactory.java

@@ -0,0 +1,47 @@
+package net.imglib2.interpolation.neighborsearch;
+
+import java.util.function.DoubleUnaryOperator;
+
+import net.imglib2.KDTree;
+import net.imglib2.RealInterval;
+import net.imglib2.RealRandomAccess;
+import net.imglib2.interpolation.InterpolatorFactory;
+import net.imglib2.type.numeric.NumericType;
+
+/**
+ * An {@link InterpolatorFactory} for {@link KDTree}s using a radial function.
+ * <p>
+ * The resulting {@link RealRandomAccess} produced by this InterpolatorFactory
+ * returns values as a linear combination of all points within a certain radius.
+ * The contribution of each point is weighted according to a function of its
+ * squared radius.
+ */
+public class RadialKDTreeInterpolatorFactory< T extends NumericType< T > > implements InterpolatorFactory< T, KDTree< T > >
+{
+	protected final double maxRadius;
+
+	protected final DoubleUnaryOperator squaredRadiusFunction;
+
+	protected final T val;
+
+	public RadialKDTreeInterpolatorFactory(
+			final DoubleUnaryOperator squaredRadiusFunction,
+			final double maxRadius, final T t )
+	{
+		this.maxRadius = maxRadius;
+		this.squaredRadiusFunction = squaredRadiusFunction;
+		this.val = t;
+	}
+
+	@Override
+	public RadialKDTreeInterpolator< T > create( final KDTree< T > tree )
+	{
+		return new RadialKDTreeInterpolator< T >( tree, squaredRadiusFunction, maxRadius, val );
+	}
+
+	@Override
+	public RealRandomAccess< T > create( final KDTree< T > tree, final RealInterval interval )
+	{
+		return create( tree );
+	}
+}