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)}
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 = 0 398 { 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 = 0 408 { 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 } 441
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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);
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.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.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);
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