opencv/modules/imgproc/src/approx.cpp

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#include "precomp.hpp"

/****************************************************************************************\
*                                  Chain Approximation                                   *
\****************************************************************************************/

typedef struct _CvPtInfo
{
    CvPoint pt;
    int k;                      /* support region */
    int s;                      /* curvature value */
    struct _CvPtInfo *next;
}
_CvPtInfo;


/* curvature: 0 - 1-curvature, 1 - k-cosine curvature. */
CvSeq* icvApproximateChainTC89( CvChain* chain, int header_size,
                                CvMemStorage* storage, int method )
{
    static const int abs_diff[] = { 1, 2, 3, 4, 3, 2, 1, 0, 1, 2, 3, 4, 3, 2, 1 };

    cv::AutoBuffer<_CvPtInfo> buf(chain->total + 8);

    _CvPtInfo       temp;
    _CvPtInfo       *array = buf, *first = 0, *current = 0, *prev_current = 0;
    int             i, j, i1, i2, s, len;
    int             count = chain->total;

    CvChainPtReader reader;
    CvSeqWriter     writer;
    CvPoint         pt = chain->origin;
    
    CV_Assert( CV_IS_SEQ_CHAIN_CONTOUR( chain ));
    CV_Assert( header_size >= (int)sizeof(CvContour) );
    
    cvStartWriteSeq( (chain->flags & ~CV_SEQ_ELTYPE_MASK) | CV_SEQ_ELTYPE_POINT,
                     header_size, sizeof( CvPoint ), storage, &writer );
    
    if( chain->total == 0 )
    {        
        CV_WRITE_SEQ_ELEM( pt, writer );
        return cvEndWriteSeq( &writer );
    }

    cvStartReadChainPoints( chain, &reader );

    temp.next = 0;
    current = &temp;

    /* Pass 0.
       Restores all the digital curve points from the chain code.
       Removes the points (from the resultant polygon)
       that have zero 1-curvature */
    for( i = 0; i < count; i++ )
    {
        int prev_code = *reader.prev_elem;

        reader.prev_elem = reader.ptr;
        CV_READ_CHAIN_POINT( pt, reader );

        /* calc 1-curvature */
        s = abs_diff[reader.code - prev_code + 7];

        if( method <= CV_CHAIN_APPROX_SIMPLE )
        {
            if( method == CV_CHAIN_APPROX_NONE || s != 0 )
            {
                CV_WRITE_SEQ_ELEM( pt, writer );
            }
        }
        else
        {
            if( s != 0 )
                current = current->next = array + i;
            array[i].s = s;
            array[i].pt = pt;
        }
    }

    //assert( pt.x == chain->origin.x && pt.y == chain->origin.y );

    if( method <= CV_CHAIN_APPROX_SIMPLE )
        return cvEndWriteSeq( &writer );

    current->next = 0;

    len = i;
    current = temp.next;

    assert( current );

    /* Pass 1.
       Determines support region for all the remained points */
    do
    {
        CvPoint pt0;
        int k, l = 0, d_num = 0;

        i = (int)(current - array);
        pt0 = array[i].pt;

        /* determine support region */
        for( k = 1;; k++ )
        {
            int lk, dk_num;
            int dx, dy;
            Cv32suf d;

            assert( k <= len );

            /* calc indices */
            i1 = i - k;
            i1 += i1 < 0 ? len : 0;
            i2 = i + k;
            i2 -= i2 >= len ? len : 0;

            dx = array[i2].pt.x - array[i1].pt.x;
            dy = array[i2].pt.y - array[i1].pt.y;

            /* distance between p_(i - k) and p_(i + k) */
            lk = dx * dx + dy * dy;

            /* distance between p_i and the line (p_(i-k), p_(i+k)) */
            dk_num = (pt0.x - array[i1].pt.x) * dy - (pt0.y - array[i1].pt.y) * dx;
            d.f = (float) (((double) d_num) * lk - ((double) dk_num) * l);

            if( k > 1 && (l >= lk || ((d_num > 0 && d.i <= 0) || (d_num < 0 && d.i >= 0))))
                break;

            d_num = dk_num;
            l = lk;
        }

        current->k = --k;

        /* determine cosine curvature if it should be used */
        if( method == CV_CHAIN_APPROX_TC89_KCOS )
        {
            /* calc k-cosine curvature */
            for( j = k, s = 0; j > 0; j-- )
            {
                double temp_num;
                int dx1, dy1, dx2, dy2;
                Cv32suf sk;

                i1 = i - j;
                i1 += i1 < 0 ? len : 0;
                i2 = i + j;
                i2 -= i2 >= len ? len : 0;

                dx1 = array[i1].pt.x - pt0.x;
                dy1 = array[i1].pt.y - pt0.y;
                dx2 = array[i2].pt.x - pt0.x;
                dy2 = array[i2].pt.y - pt0.y;

                if( (dx1 | dy1) == 0 || (dx2 | dy2) == 0 )
                    break;

                temp_num = dx1 * dx2 + dy1 * dy2;
                temp_num =
                    (float) (temp_num /
                             sqrt( ((double)dx1 * dx1 + (double)dy1 * dy1) *
                                   ((double)dx2 * dx2 + (double)dy2 * dy2) ));
                sk.f = (float) (temp_num + 1.1);

                assert( 0 <= sk.f && sk.f <= 2.2 );
                if( j < k && sk.i <= s )
                    break;

                s = sk.i;
            }
            current->s = s;
        }
        current = current->next;
    }
    while( current != 0 );

    prev_current = &temp;
    current = temp.next;

    /* Pass 2.
       Performs non-maxima supression */
    do
    {
        int k2 = current->k >> 1;

        s = current->s;
        i = (int)(current - array);

        for( j = 1; j <= k2; j++ )
        {
            i2 = i - j;
            i2 += i2 < 0 ? len : 0;

            if( array[i2].s > s )
                break;

            i2 = i + j;
            i2 -= i2 >= len ? len : 0;

            if( array[i2].s > s )
                break;
        }

        if( j <= k2 )           /* exclude point */
        {
            prev_current->next = current->next;
            current->s = 0;     /* "clear" point */
        }
        else
            prev_current = current;
        current = current->next;
    }
    while( current != 0 );

    /* Pass 3.
       Removes non-dominant points with 1-length support region */
    current = temp.next;
    assert( current );
    prev_current = &temp;

    do
    {
        if( current->k == 1 )
        {
            s = current->s;
            i = (int)(current - array);

            i1 = i - 1;
            i1 += i1 < 0 ? len : 0;

            i2 = i + 1;
            i2 -= i2 >= len ? len : 0;

            if( s <= array[i1].s || s <= array[i2].s )
            {
                prev_current->next = current->next;
                current->s = 0;
            }
            else
                prev_current = current;
        }
        else
            prev_current = current;
        current = current->next;
    }
    while( current != 0 );

    if( method == CV_CHAIN_APPROX_TC89_KCOS )
        goto copy_vect;

    /* Pass 4.
       Cleans remained couples of points */
    assert( temp.next );

    if( array[0].s != 0 && array[len - 1].s != 0 )      /* specific case */
    {
        for( i1 = 1; i1 < len && array[i1].s != 0; i1++ )
        {
            array[i1 - 1].s = 0;
        }
        if( i1 == len )
            goto copy_vect;     /* all points survived */
        i1--;

        for( i2 = len - 2; i2 > 0 && array[i2].s != 0; i2-- )
        {
            array[i2].next = 0;
            array[i2 + 1].s = 0;
        }
        i2++;

        if( i1 == 0 && i2 == len - 1 )  /* only two points */
        {
            i1 = (int)(array[0].next - array);
            array[len] = array[0];      /* move to the end */
            array[len].next = 0;
            array[len - 1].next = array + len;
        }
        temp.next = array + i1;
    }

    current = temp.next;
    first = prev_current = &temp;
    count = 1;

    /* do last pass */
    do
    {
        if( current->next == 0 || current->next - current != 1 )
        {
            if( count >= 2 )
            {
                if( count == 2 )
                {
                    int s1 = prev_current->s;
                    int s2 = current->s;

                    if( s1 > s2 || (s1 == s2 && prev_current->k <= current->k) )
                        /* remove second */
                        prev_current->next = current->next;
                    else
                        /* remove first */
                        first->next = current;
                }
                else
                    first->next->next = current;
            }
            first = current;
            count = 1;
        }
        else
            count++;
        prev_current = current;
        current = current->next;
    }
    while( current != 0 );

copy_vect:

    // gather points
    current = temp.next;
    assert( current );

    do
    {
        CV_WRITE_SEQ_ELEM( current->pt, writer );
        current = current->next;
    }
    while( current != 0 );

    return cvEndWriteSeq( &writer );
}


/*Applies some approximation algorithm to chain-coded contour(s) and
  converts it/them to polygonal representation */
CV_IMPL CvSeq*
cvApproxChains( CvSeq*              src_seq,
                CvMemStorage*       storage,
                int                 method,
                double              /*parameter*/, 
                int                 minimal_perimeter, 
                int                 recursive )
{
    CvSeq *prev_contour = 0, *parent = 0;
    CvSeq *dst_seq = 0;
    
    if( !src_seq || !storage )
        CV_Error( CV_StsNullPtr, "" );
    if( method > CV_CHAIN_APPROX_TC89_KCOS || method <= 0 || minimal_perimeter < 0 )
        CV_Error( CV_StsOutOfRange, "" );

    while( src_seq != 0 )
    {
        int len = src_seq->total;

        if( len >= minimal_perimeter )
        {
            CvSeq *contour = 0;
            
            switch( method )
            {
            case CV_CHAIN_APPROX_NONE:
            case CV_CHAIN_APPROX_SIMPLE:
            case CV_CHAIN_APPROX_TC89_L1:
            case CV_CHAIN_APPROX_TC89_KCOS:
                contour = icvApproximateChainTC89( (CvChain *) src_seq, sizeof( CvContour ), storage, method );
                break;
            default:
                CV_Error( CV_StsOutOfRange, "" );
            }

            if( contour->total > 0 )
            {
                cvBoundingRect( contour, 1 );

                contour->v_prev = parent;
                contour->h_prev = prev_contour;

                if( prev_contour )
                    prev_contour->h_next = contour;
                else if( parent )
                    parent->v_next = contour;
                prev_contour = contour;
                if( !dst_seq )
                    dst_seq = prev_contour;
            }
            else                /* if resultant contour has zero length, skip it */
            {
                len = -1;
            }
        }

        if( !recursive )
            break;

        if( src_seq->v_next && len >= minimal_perimeter )
        {
            assert( prev_contour != 0 );
            parent = prev_contour;
            prev_contour = 0;
            src_seq = src_seq->v_next;
        }
        else
        {
            while( src_seq->h_next == 0 )
            {
                src_seq = src_seq->v_prev;
                if( src_seq == 0 )
                    break;
                prev_contour = parent;
                if( parent )
                    parent = parent->v_prev;
            }
            if( src_seq )
                src_seq = src_seq->h_next;
        }
    }

    return dst_seq;
}


/****************************************************************************************\
*                               Polygonal Approximation                                  *
\****************************************************************************************/

/* Ramer-Douglas-Peucker algorithm for polygon simplification */

/* the version for integer point coordinates */
template<typename T> static CvSeq*
icvApproxPolyDP( CvSeq* src_contour, int header_size, 
                 CvMemStorage* storage, double eps )
{
    typedef cv::Point_<T> PT;
    int             init_iters = 3;
    CvSlice         slice = {0, 0}, right_slice = {0, 0};
    CvSeqReader     reader, reader2;
    CvSeqWriter     writer;
    PT              start_pt(-1000000, -1000000), end_pt(0, 0), pt(0,0);
    int             i = 0, j, count = src_contour->total, new_count;
    int             is_closed = CV_IS_SEQ_CLOSED( src_contour );
    bool            le_eps = false;
    CvMemStorage*   temp_storage = 0;
    CvSeq*          stack = 0;
    CvSeq*          dst_contour;
    
    assert( CV_SEQ_ELTYPE(src_contour) == cv::DataType<PT>::type );
    cvStartWriteSeq( src_contour->flags, header_size, sizeof(pt), storage, &writer );

    if( src_contour->total == 0  )
        return cvEndWriteSeq( &writer );

    temp_storage = cvCreateChildMemStorage( storage );

    assert( src_contour->first != 0 );
    stack = cvCreateSeq( 0, sizeof(CvSeq), sizeof(CvSlice), temp_storage );
    eps *= eps;
    cvStartReadSeq( src_contour, &reader, 0 );

    if( !is_closed )
    {
        right_slice.start_index = count;
        end_pt = *(PT*)(reader.ptr);
        start_pt = *(PT*)cvGetSeqElem( src_contour, -1 );

        if( start_pt.x != end_pt.x || start_pt.y != end_pt.y )
        {
            slice.start_index = 0;
            slice.end_index = count - 1;
            cvSeqPush( stack, &slice );
        }
        else
        {
            is_closed = 1;
            init_iters = 1;
        }
    }
    
    if( is_closed )
    {
        /* 1. Find approximately two farthest points of the contour */
        right_slice.start_index = 0;

        for( i = 0; i < init_iters; i++ )
        {
            double dist, max_dist = 0;
            cvSetSeqReaderPos( &reader, right_slice.start_index, 1 );
            CV_READ_SEQ_ELEM( start_pt, reader );   /* read the first point */

            for( j = 1; j < count; j++ )
            {
                double dx, dy;

                CV_READ_SEQ_ELEM( pt, reader );
                dx = pt.x - start_pt.x;
                dy = pt.y - start_pt.y;

                dist = dx * dx + dy * dy;

                if( dist > max_dist )
                {
                    max_dist = dist;
                    right_slice.start_index = j;
                }
            }

            le_eps = max_dist <= eps;
        }

        /* 2. initialize the stack */
        if( !le_eps )
        {
            slice.start_index = cvGetSeqReaderPos( &reader );
            slice.end_index = right_slice.start_index += slice.start_index;

            right_slice.start_index -= right_slice.start_index >= count ? count : 0;
            right_slice.end_index = slice.start_index;
            if( right_slice.end_index < right_slice.start_index )
                right_slice.end_index += count;

            cvSeqPush( stack, &right_slice );
            cvSeqPush( stack, &slice );
        }
        else
            CV_WRITE_SEQ_ELEM( start_pt, writer );
    }

    /* 3. run recursive process */
    while( stack->total != 0 )
    {
        cvSeqPop( stack, &slice );

        cvSetSeqReaderPos( &reader, slice.end_index );
        CV_READ_SEQ_ELEM( end_pt, reader );

        cvSetSeqReaderPos( &reader, slice.start_index );
        CV_READ_SEQ_ELEM( start_pt, reader );

        if( slice.end_index > slice.start_index + 1 )
        {
            double dx, dy, dist, max_dist = 0;

            dx = end_pt.x - start_pt.x;
            dy = end_pt.y - start_pt.y;

            assert( dx != 0 || dy != 0 );

            for( i = slice.start_index + 1; i < slice.end_index; i++ )
            {
                CV_READ_SEQ_ELEM( pt, reader );
                dist = fabs((pt.y - start_pt.y) * dx - (pt.x - start_pt.x) * dy);

                if( dist > max_dist )
                {
                    max_dist = dist;
                    right_slice.start_index = i;
                }
            }

            le_eps = max_dist * max_dist <= eps * (dx * dx + dy * dy);
        }
        else
        {
            assert( slice.end_index > slice.start_index );
            le_eps = true;
            /* read starting point */
            cvSetSeqReaderPos( &reader, slice.start_index );
            CV_READ_SEQ_ELEM( start_pt, reader );
        }

        if( le_eps )
        {
            CV_WRITE_SEQ_ELEM( start_pt, writer );
        }
        else
        {
            right_slice.end_index = slice.end_index;
            slice.end_index = right_slice.start_index;
            cvSeqPush( stack, &right_slice );
            cvSeqPush( stack, &slice );
        }
    }

    is_closed = CV_IS_SEQ_CLOSED( src_contour );
    if( !is_closed )
        CV_WRITE_SEQ_ELEM( end_pt, writer );

    dst_contour = cvEndWriteSeq( &writer );
    
    // last stage: do final clean-up of the approximated contour -
    // remove extra points on the [almost] stright lines. 
    
    cvStartReadSeq( dst_contour, &reader, is_closed );
    CV_READ_SEQ_ELEM( start_pt, reader );

    reader2 = reader;
    CV_READ_SEQ_ELEM( pt, reader );

    new_count = count = dst_contour->total;
    for( i = !is_closed; i < count - !is_closed && new_count > 2; i++ )
    {
        double dx, dy, dist;
        CV_READ_SEQ_ELEM( end_pt, reader );

        dx = end_pt.x - start_pt.x;
        dy = end_pt.y - start_pt.y;
        dist = fabs((pt.x - start_pt.x)*dy - (pt.y - start_pt.y)*dx);
        if( dist * dist <= 0.5*eps*(dx*dx + dy*dy) && dx != 0 && dy != 0 )
        {
            new_count--;
            *((PT*)reader2.ptr) = start_pt = end_pt;
            CV_NEXT_SEQ_ELEM( sizeof(pt), reader2 );
            CV_READ_SEQ_ELEM( pt, reader );
            i++;
            continue;
        }
        *((PT*)reader2.ptr) = start_pt = pt;
        CV_NEXT_SEQ_ELEM( sizeof(pt), reader2 );
        pt = end_pt;
    }

    if( !is_closed )
        *((PT*)reader2.ptr) = pt;

    if( new_count < count )
        cvSeqPopMulti( dst_contour, 0, count - new_count );

    cvReleaseMemStorage( &temp_storage );
    return dst_contour;
}


CV_IMPL CvSeq*
cvApproxPoly( const void*  array, int  header_size,
              CvMemStorage*  storage, int  method, 
              double  parameter, int parameter2 )
{
    CvSeq* dst_seq = 0;
    CvSeq *prev_contour = 0, *parent = 0;
    CvContour contour_header;
    CvSeq* src_seq = 0;
    CvSeqBlock block;
    int recursive = 0;

    if( CV_IS_SEQ( array ))
    {
        src_seq = (CvSeq*)array;
        if( !CV_IS_SEQ_POLYLINE( src_seq ))
            CV_Error( CV_StsBadArg, "Unsupported sequence type" );

        recursive = parameter2;

        if( !storage )
            storage = src_seq->storage;
    }
    else
    {
        src_seq = cvPointSeqFromMat(
            CV_SEQ_KIND_CURVE | (parameter2 ? CV_SEQ_FLAG_CLOSED : 0),
            array, &contour_header, &block );
    }

    if( !storage )
        CV_Error( CV_StsNullPtr, "NULL storage pointer " );

    if( header_size < 0 )
        CV_Error( CV_StsOutOfRange, "header_size is negative. "
                  "Pass 0 to make the destination header_size == input header_size" );

    if( header_size == 0 )
        header_size = src_seq->header_size;

    if( !CV_IS_SEQ_POLYLINE( src_seq ))
    {
        if( CV_IS_SEQ_CHAIN( src_seq ))
        {
            CV_Error( CV_StsBadArg, "Input curves are not polygonal. "
                                    "Use cvApproxChains first" );
        }
        else
        {
            CV_Error( CV_StsBadArg, "Input curves have uknown type" );
        }
    }

    if( header_size == 0 )
        header_size = src_seq->header_size;

    if( header_size < (int)sizeof(CvContour) )
        CV_Error( CV_StsBadSize, "New header size must be non-less than sizeof(CvContour)" );

    if( method != CV_POLY_APPROX_DP )
        CV_Error( CV_StsOutOfRange, "Unknown approximation method" );

    while( src_seq != 0 )
    {
        CvSeq *contour = 0;

        switch (method)
        {
        case CV_POLY_APPROX_DP:
            if( parameter < 0 )
                CV_Error( CV_StsOutOfRange, "Accuracy must be non-negative" );

            if( CV_SEQ_ELTYPE(src_seq) == CV_32SC2 )
                contour = icvApproxPolyDP<int>( src_seq, header_size, storage, parameter );
            else
                contour = icvApproxPolyDP<float>( src_seq, header_size, storage, parameter );
            break;
        default:
            assert(0);
            CV_Error( CV_StsBadArg, "Invalid approximation method" );
        }

        assert( contour );

        if( header_size >= (int)sizeof(CvContour))
            cvBoundingRect( contour, 1 );

        contour->v_prev = parent;
        contour->h_prev = prev_contour;

        if( prev_contour )
            prev_contour->h_next = contour;
        else if( parent )
            parent->v_next = contour;
        prev_contour = contour;
        if( !dst_seq )
            dst_seq = prev_contour;

        if( !recursive )
            break;

        if( src_seq->v_next )
        {
            assert( prev_contour != 0 );
            parent = prev_contour;
            prev_contour = 0;
            src_seq = src_seq->v_next;
        }
        else
        {
            while( src_seq->h_next == 0 )
            {
                src_seq = src_seq->v_prev;
                if( src_seq == 0 )
                    break;
                prev_contour = parent;
                if( parent )
                    parent = parent->v_prev;
            }
            if( src_seq )
                src_seq = src_seq->h_next;
        }
    }

    return dst_seq;
}

/* End of file. */