reduce spatial function in itaHRTF

applications/Binaural-HRTF/HRTF_class/@itaHRTF/reduce_spatial.m

@@ -14,5 +14,44 @@ function [ cThis ] = reduce_spatial( this, newCoordinates, varargin )
 % Author:  Jan-Gerrit Richter <jri@akustik.rwth-aachen.de>
 % Version: 2017-11-23
 
+oldCoords = this.getEar('L').channelCoordinates;
+
+% if the desired sampling has more points, its probably unfeasable with
+% findnearest search. Abort
+if oldCoords.nPoints < newCoordinates.nPoints
+    error('There are more points in the wanted sampling than are available. You probably want the interp function');
 end
 
+% the new coords should have the same radius as the old ones to reduce
+% errors
+newCoordinates.r = mean(oldCoords.r);
+
+
+oldCoords = oldCoords.build_search_database;
+
+newIndex = oldCoords.findnearest(newCoordinates);
+
+% calculate all distances from the wanted points to the found points
+pointDistances = getVectorLength(newCoordinates,oldCoords.n(newIndex));
+
+% calculate the distance between two neighboring points of the new sampling
+newSamplingDistance = getVectorLength(newCoordinates.n(1),newCoordinates.n(2));
+
+% the maximum of the found points should always be smaller
+if max(pointDistances) > newSamplingDistance
+   error('The found points are further apart than the sampling allows. Something is wrong') 
+end
+
+
+cThis = this.direction(newIndex);
+
+end
+
+
+function length = getVectorLength(pointsA, pointsB)
+    
+    pointsA.r = pointsB.r;
+    vector = pointsA - pointsB;
+    length = sqrt(vector.x.^2 + vector.y.^2 + vector.z.^2);
+
+end
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