/*
* Copyright (c) 2011-2015, Peter Abeles. All Rights Reserved.
*
* This file is part of BoofCV (http://boofcv.org).
*
* 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 boofcv.alg.shapes.polyline;
import georegression.geometry.UtilPoint2D_I32;
import georegression.metric.Distance2D_F64;
import georegression.struct.point.Point2D_I32;
import org.ddogleg.struct.GrowQueue_I32;
import java.util.List;
/**
* Implementation of {@link SplitMergeLineFit} for looped lists of points. The beginning and end of the list are
* assumed to be connected. An additional check is done in the start to find two points which are far apart.
*
* @author Peter Abeles
*/
// TODO only check lines that changed for splitting
public class SplitMergeLineFitLoop extends SplitMergeLineFit {
// number of points in the contour
protected int N;
/**
* @see SplitMergeLineFit#SplitMergeLineFit(double,double, int)
*/
public SplitMergeLineFitLoop(double splitFraction,
double minimumSplitFraction,
int maxIterations)
{
super(splitFraction,minimumSplitFraction, maxIterations);
}
@Override
public boolean process( List<Point2D_I32> contour ) {
this.contour = contour;
this.N = contour.size();
this.minimumSideLengthPixel = (int)Math.ceil(N* minimumSideLengthFraction);
// ------------- find initial line segments
splits.reset();
// can't fit a line to a single point
if( N <= 1 ) {
return false;
}
// Go around the contour looking for two points on opposite ends which are far apart
int startIndex = selectFarthest(contour);
int middleIndex = (startIndex+N/2)%N;
// split each half recursively
splits.add(startIndex);
splitPixels(startIndex, N / 2);
splits.add(middleIndex);
splitPixels(middleIndex, N - (N / 2));
// ------------ Refine the initial segments by splitting and merging each segment
if( splits.size <= 2 )
return false; // can't merge a single line
// System.out.println("Enter loop");
for( int i = 0; i < maxIterations; i++ ) {
boolean merged = mergeSegments();
if( splits.size() <= 0)
return false;
if( !merged && !splitSegments() )
break;
if( splits.size() <= 2 || splits.size() >= abortSplits )
return false;
}
return true;
}
/**
* Recursively splits pixels between indexStart to indexStart+length. A split happens if there is a pixel
* more than the desired distance away from the two end points. Results are placed into 'splits'
*/
protected void splitPixels(int indexStart, int length) {
// too short to split
if( length < minimumSideLengthPixel)
return;
// end points of the line
int indexEnd = (indexStart+length)%N;
int splitOffset = selectSplitOffset(indexStart,length);
if( splitOffset >= 0 ) {
// System.out.println(" splitting ");
splitPixels(indexStart, splitOffset);
int indexSplit = (indexStart+splitOffset)%N;
splits.add(indexSplit);
splitPixels(indexSplit, circularDistance(indexSplit, indexEnd));
}
}
/**
* Computes the distance between pairs of points which are separated by 1/2 the contour list. The index of the
* first pixel in the pair with the greatest distance is returned
* @return Index of the first pixel which should be used to split the list. The other end is ret + N/2
*/
protected int selectFarthest( List<Point2D_I32> contour ) {
int bestIndex = -1;
int bestDistance = 0;
int N = contour.size();
int half = N/2;
for( int i = 0; i < half; i++ ) {
int end = (i+half)%N;
Point2D_I32 a = contour.get(i);
Point2D_I32 b = contour.get(end);
int dist = UtilPoint2D_I32.distanceSq(a.x,a.y,b.x,b.y);
if( bestDistance < dist ) {
bestIndex = i;
bestDistance = dist;
}
}
// if( bestIndex == -1 )
// System.out.println();
return bestIndex;
}
/**
* Merges lines together if the common corner is close to a common line
* @return true the list being changed
*/
protected boolean mergeSegments() {
// See if merging will cause a degenerate case
if( splits.size() <= 3 )
return false;
boolean change = false;
work.reset();
for( int i = 0; i < splits.size; i++ ) {
int start = splits.data[i];
int end = splits.data[(i+2)%splits.size];
if( selectSplitOffset(start,circularDistance(start,end)) < 0 ) {
// merge the two lines by not adding it
change = true;
} else {
work.add(splits.data[(i + 1)%splits.size]);
}
}
// swap the two lists
GrowQueue_I32 tmp = work;
work = splits;
splits = tmp;
return change;
}
/**
* Splits a line in two if there is a point that is too far away
* @return true for change
*/
protected boolean splitSegments() {
boolean change = false;
work.reset();
for( int i = 0; i < splits.size-1; i++ ) {
change |= checkSplit(change, i,i+1);
}
change |= checkSplit(change, splits.size - 1, 0);
// swap the two lists
GrowQueue_I32 tmp = work;
work = splits;
splits = tmp;
return change;
}
private boolean checkSplit(boolean change, int i0 , int i1) {
int start = splits.data[i0];
int end = splits.data[i1];
int length = circularDistance(start, end);
int bestOffset = selectSplitOffset(start,length);
if( bestOffset >= 0 ) {
change = true;
work.add(start);
work.add((start+bestOffset)%N);
} else {
work.add(start);
}
return change;
}
/**
* Finds the point between indexStart and the end point which is the greater distance from the line
* (set up prior to calling). Returns the index of the element with a distances greater than tolerance, otherwise -1
*/
protected int selectSplitOffset( int indexStart , int length ) {
int bestOffset = -1;
int indexEnd = (indexStart + length) % N;
Point2D_I32 startPt = contour.get(indexStart);
Point2D_I32 endPt = contour.get(indexEnd);
line.p.set(startPt.x,startPt.y);
line.slope.set(endPt.x-startPt.x,endPt.y-startPt.y);
double bestDistanceSq = splitThresholdSq(contour.get(indexStart), contour.get(indexEnd));
// adjusting using 'minimumSideLengthPixel' to ensure it doesn't create a new line which is too short
int minLength = Math.max(1,minimumSideLengthPixel);// 1 is the minimum so that you don't split on the same corner
length -= minLength;
for( int i = minLength; i <= length; i++ ) {
Point2D_I32 b = contour.get((indexStart+i)%N);
point2D.set(b.x,b.y);
double dist = Distance2D_F64.distanceSq(line, point2D);
if( dist >= bestDistanceSq ) {
bestDistanceSq = dist;
bestOffset = i;
}
}
return bestOffset;
}
/**
* Distance the two points are apart in clockwise direction
*/
protected int circularDistance( int start , int end ) {
if( end >= start )
return end-start;
else
return N-start+end;
}
}