How to use Cvb.Foundation.CreateCircle2DByRegression


I am struggling to work out how to use Cvb.Foundation.CreateCircle2DByRegression but it always returns 0 and I am not sure what I am missing:

       Cvb.Image.PIXELLIST pIXELLIST= Cvb.Image.CreatePixelList(2);    
       //double[] values = new double[pixels.Count * 2];
      //for (int i = 0; i < pixels.Count; ++i)
      //  values[i * 2] = pixels[i].X;
      //  values[i * 2 + 1] = pixels[i].Y;

      double[] values = { 0, 1, -1, 0, 1, 0 };
      bool success = Cvb.Image.AddPixel(pIXELLIST, values);
      var cicrleRes = Cvb.Foundation.CreateCircle2DByRegression(pIXELLIST);

Any ideas would be appreciated.

Hi @Amicelli

I have an example, I just looked it up… it is VB6 :open_mouth: but let’s look at the logic

  1. creating a pixellist, in my case I’ve incorporated it into a threshold operation from a scrollbar. It looks like you are ok there.
pixelList = CreatePixelList(2)
For x = 1 To xdim - 1
    For y = 1 To ydim - 1
        gl = PixVal(imghandle, 0, x, y)
        If gl < HScrThresh.Value Then
            point(Index) = x
            point(Index + 1) = y
            result = AddPixel(pixelList, point(Index))
            Index = Index + 2
        End If
  1. after that it is easy… try these functions:

circleOutput = CreateCircle2DByRegression(pixelList)

result = GetCircle2DCenter(circleOutput, ctrX, ctrY)
result = GetCircle2DRadius(circleOutput, radius)

  1. and a display?

circPos(0).x = ctrX
circPos(0).y = ctrY
circPos(1).x = point(21)
circPos(1).y = point(22)

CVdisplay1.AddOverlayObject “Circle”, “Circle”, False, False, vbRed, vbGreen, False, 1, circPos(0).x, ObjectData

Hello Amicelli,

each pixel you add with AddPixel represents one coordinate ( x and y) on your circle. So you need to add every pixel value individually .

For example:

double[] value1 = { 2, 1 };
double[] value2 = { 3, 2 };
double[] value3 = { 2, 3 };
double[] value4 = { 1, 2 };
Image.AddPixel(pl, value1);
Image.AddPixel(pl, value2);
Image.AddPixel(pl, value3);
Image.AddPixel(pl, value4);


Hello @JonV,

this worked fine when I used a given set of values:

      Cvb.Image.PIXELLIST pIXELLIST = Cvb.Image.CreatePixelList(2);

      bool success = Cvb.Image.AddPixel(pIXELLIST, new double[] { -1, 0 });
      success = Cvb.Image.AddPixel(pIXELLIST, new double[] { 0, 1 });
      success = Cvb.Image.AddPixel(pIXELLIST, new double[] { 1, 0 });

      var cicrleRes = Cvb.Foundation.CreateCircle2DByRegression(pIXELLIST); 

But as soon as I put all the values from this image in there it was throwing an exception.


Any ideas why?


Hi @Amicelli,

Two questions:

  1. How many points did you add? You said “all”, but I find it hard to believe that you’d try to fit a circle through all the white dots in the image.
  2. Would it be possible to hand in a crash dump to

Generally: The edge image you show does not really contain a circle, the structure to me looks elliptic (as if looking at a circle from an angle), so even if the regression does yield a result, it will probably be a fairly poor match to a circle.

Hello @illusive.

thanks for coming back to me and sorry for the late reply as I started to do something else and disregarded this approach.

I did try to replicate it again, but it does not seem to crash (if I use the supplied image). New application. Maybe something was corrupt while I was handling it in my main application… who knows…

My hope was that it would give me the best circle regardless how much “crap” I put in.

However, you are right, the form I want to look at is elliptical. Unfortunately, this adds much more to the complexity. I did try hough circles (which went all over the place) and I am currently looking at smallest enclosing circles (I was thinking of using smallest enclosing ellipsoids but it adds too many unknowns and for the first version it might be enough).

Anyhow, thanks for your help.