c#如何按顺时针顺序（tl、tr、br、bl）排列4个点的列表，以便在opencv getPerspective中使用？

Question

我正在使用c#中的opencv来检测网络摄像头图像中的轮廓。如果轮廓有4个点，我想使用opencv的getPerspective和warpPerspective来校正轮廓中包含的像素的透视图。功能。你知道吗

下面是获得这4个点的代码：

    Imgproc.approxPolyDP(perimMat,polyMat,0.005 * perim, true); //get contour of the current detected perimeter as polyMat
    List<Point> polyMatList = polyMat.toList(); //convert it to a list of points
    if (polyMatList.Count == 4){ //this contour has 4 points, we can use it for getting perspective
      Debug.Log("p1x: " + polyMatList[0].x + "p1y: " + polyMatList[0].y); //example log: p1x: 203,p1y: 111
    }

现在我有了这个点列表，我需要确定它的顺序是左上，右上，右下，左下，这样我就可以在getPerspective中使用它了。我该怎么做？你知道吗

我见过其他语言的例子，但它们通常使用numpy之类的东西来进行排序。我对C#（使用它是因为统一）有点陌生，但我假设有一些辅助方法可以从中借鉴。你知道吗

This gist到目前为止是我调整透视图的主要指南，for_point_warp函数似乎提供了一个不错的指南。我只是不知道c的等价物。你知道吗

Answer 1

以下是我基于this tutorial实现的内容（尽管我确信我可以做一些更优雅的事情）。你知道吗

polyMat.convertTo(orientationMat, CvType.CV_32S); //conver MatOfPoint2f back to MatofPoint so it can be drawn
//sort by y val

polyMatList = polyMatList.OrderBy(p => p.x).ToList();

List<Point> leftmostPts = new List<Point>();
leftmostPts.Add(polyMatList[0]);
leftmostPts.Add(polyMatList[1]);

List<Point> rightmostPts = new List<Point>();
rightmostPts.Add(polyMatList[2]);
rightmostPts.Add(polyMatList[3]);

//we now have a top left point
leftmostPts = leftmostPts.OrderBy(p => p.y).ToList();

//calculate distance from top left to rightmost 2 points:
double dX0 = rightmostPts[0].x - leftmostPts[0].x;
double dY0 = rightmostPts[0].y - leftmostPts[0].y;
double d0 = Math.Sqrt(dX0 * dX0 + dY0 * dY0); 

double dX1 = rightmostPts[1].x - leftmostPts[0].x;
double dY1 = rightmostPts[1].y - leftmostPts[0].y;
double d1 = Math.Sqrt(dX1 * dX1 + dY1 * dY1);

List<Point> orderedPolyMat = new List<Point>();
orderedPolyMat.Add(leftmostPts[0]);
if (d0 > d1){ //greatest distance between right two points will be bottom right
    orderedPolyMat.Add(rightmostPts[1]);
    orderedPolyMat.Add(rightmostPts[0]);
} else {
    orderedPolyMat.Add(rightmostPts[0]);
    orderedPolyMat.Add(rightmostPts[1]);
}
orderedPolyMat.Add(leftmostPts[1]);

Answer 2

//Begin by sorting your list by y values using List.sort()

polyMatList.sort( (pnt_a, pnt_b) => pnt_b.y - pnt_a.y ); // points 0 & 1 will by definition be your top points and points 2, 3 will be definition be your bottom points.

// now your top 2 points may be out of order since we only sorted by y in the previous step
Point tempPoint;

if(polyMatList[0].x > polyMatList[1].x)
{
   tempPoint = polyMatList[0];
   polyMatList[0] = polyMatList[1];
   polyMatList[1] = tempPoint ;
}

// same goes for your bottom two points 
if(polyMatList[2].x > polyMatList[3].x)
{
   tempPoint = polyMatList[2];
   polyMatList[2] = polyMatList[3];
   polyMatList[3] = tempPoint ;
}

//now your list will be ordered tl, tr, bl, br