minAreaRect-OpenCV

由于要将rRect利用仿射变换裁剪下来并旋正，需要知道rRect.point()的四个点的位置，查了一下资料，记在下面：

简介：Finds a circumscribed rectangle of the minimal area for 2D point set by building convex hull for the set and applying rotating calipers4 technique to the hull.1 建立外凸包，应用旋转卡尺技术来求2维点的最小面积包围矩形。 API reference OpenCV官方例程

源码： OpenCV249/opencv/sources/modules/imgPRoc/src/contours.cpp 1910行-1916行

cv::RotatedRect cv::minAreaRect( InputArray _points ){    Mat points = _points.getMat();    CV_Assert(points.checkVector(2) >= 0 && (points.depth() == CV_32F || points.depth() == CV_32S));    CvMat _cpoints = points;    return cvMinAreaRect2(&_cpoints, 0);}12345671234567
cvMinAreaRect2： 2
http://fossies.org/dox/OpenCV-2.4.4a/rotcalipers_8cpp_source.html 截取自第347行
 347 CV_IMPL  CvBox2D  348 cvMinAreaRect2( const CvArr* array, CvMemStorage* storage )  349 {  350     cv::Ptr<CvMemStorage> temp_storage;  351     CvBox2D box;  352     cv::AutoBuffer<CvPoint2D32f> _points;  353     CvPoint2D32f* points;  354   355     memset(&box, 0, sizeof(box));  356   357     int i, n;  358     CvSeqReader reader;  359     CvContour contour_header;  360     CvSeqBlock block;  361     CvSeq* ptseq = (CvSeq*)array;  362     CvPoint2D32f out[3];  363   364     if( CV_IS_SEQ(ptseq) )  365     {  366         if( !CV_IS_SEQ_POINT_SET(ptseq) &&  367             (CV_SEQ_KIND(ptseq) != CV_SEQ_KIND_CURVE ||  368             CV_SEQ_ELTYPE(ptseq) != CV_SEQ_ELTYPE_PPOINT ))  369             CV_Error( CV_StsUnsupportedFormat,  370                 "Input sequence must consist of 2d points or pointers to 2d points" );  371         if( !storage )  372             storage = ptseq->storage;  373     }  374     else  375     {  376         ptseq = cvPointSeqFromMat( CV_SEQ_KIND_GENERIC, array, &contour_header, &block );  377     }  378   379     if( storage )  380     {  381         temp_storage = cvCreateChildMemStorage( storage );  382     }  383     else  384     {  385         temp_storage = cvCreateMemStorage(1 << 10);  386     }  387   388     ptseq = cvConvexHull2( ptseq, temp_storage, CV_CLOCKWISE, 1 );  389     n = ptseq->total;  390   391     _points.allocate(n);  392     points = _points;  393     cvStartReadSeq( ptseq, &reader );  394   395     if( CV_SEQ_ELTYPE( ptseq ) == CV_32SC2 )  396     {  397         for( i = 0; i < n; i++ )  398         {  399             CvPoint pt;  400             CV_READ_SEQ_ELEM( pt, reader );  401             points[i].x = (float)pt.x;  402             points[i].y = (float)pt.y;  403         }  404     }  405     else  406     {  407         for( i = 0; i < n; i++ )  408         {  409             CV_READ_SEQ_ELEM( points[i], reader );  410         }  411     }  412   413     if( n > 2 )  414     {  415         icvRotatingCalipers( points, n, CV_CALIPERS_MINAREARECT, (float*)out );  416         box.center.x = out[0].x + (out[1].x + out[2].x)*0.5f;  417         box.center.y = out[0].y + (out[1].y + out[2].y)*0.5f;  418         box.size.width = (float)sqrt((double)out[1].x*out[1].x + (double)out[1].y*out[1].y);  419         box.size.height = (float)sqrt((double)out[2].x*out[2].x + (double)out[2].y*out[2].y);  420         box.angle = (float)atan2( (double)out[1].y, (double)out[1].x );  421     }  422     else if( n == 2 )  423     {  424         box.center.x = (points[0].x + points[1].x)*0.5f;  425         box.center.y = (points[0].y + points[1].y)*0.5f;  426         double dx = points[1].x - points[0].x;  427         double dy = points[1].y - points[0].y;  428         box.size.width = (float)sqrt(dx*dx + dy*dy);  429         box.size.height = 0;  430         box.angle = (float)atan2( dy, dx );  431     }  432     else  433     {  434         if( n == 1 )  435             box.center = points[0];  436     }  437   438     box.angle = (float)(box.angle*180/CV_PI);  439     return box;  440 }  44112345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091929394951234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495
OpenCV以图像的左上角为(0,0)，Point(x,y)，x对应列，y对应行，
RotatedRect rRect;rRect = minAreaRect(point);Point2f vertices[4];rRect.points(vertices);12341234
rRect.size.width，rRect.size.height，rRect.angle，vertices[0]，vertices[1]，vertices[2]，vertices[3]如下图所示，和mine1024博客3里Cvbox2D好像不太一样,改天验证下。
利用仿射变换，将该区域裁剪下来，并旋正：
    vector<Point> point;    vector<vector<Point>> contours ;    findContours( Itwe, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE );    if(!contours.size())    {        printf("No contours!/n");        return 0;    }    else    {        double maxarea = 0;        int maxareai = 0;        for (int i = 0; i<contours.size(); i++)        {            double tmparea = fabs(contourArea(contours[i]));            if(tmparea > maxarea)            {tmparea = tmparea;            maxareai = i;}          }        vector<Point> contourspoint = contours[maxareai];    }    RotatedRect rRect;    rRect = minAreaRect(point);    int dstw,dsth;    Point2f vertices[4];    Point2f verdst[4];    if(rRect.size.width>rRect.size.height)    {        //rRect.size.width += 100;  //宽度增加100，以防定位偏差        rRect.points(vertices);        dstw = rRect.size.width;        dsth = rRect.size.height;        verdst[0] = Point2f(0,dsth);        verdst[1] = Point2f(0,0);        verdst[2] = Point2f(dstw,0);        verdst[3] = Point2f(dstw,dsth);     }    else     {        //rRect.size.height += 100;        rRect.points(vertices);        dstw = rRect.size.height;        dsth = rRect.size.width;        verdst[0] = Point2f(dstw,dsth);        verdst[1] = Point2f(0,dsth);        verdst[2] = Point2f(0,0);        verdst[3] = Point2f(dstw,0);    }    Mat Idst = Mat(dsth,dstw,CV_8UC1);    Mat warpMatrix = getPerspectiveTransform(vertices, verdst);    warpPerspective(Isrc, Idst, warpMatrix, Idst.size(), INTER_LINEAR, BORDER_CONSTANT);