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[Java OpenCV] Fatal error in Imgproc.arcLength

asked 2013-07-10 09:14:52 -0500

Sodat gravatar image

updated 2013-07-10 09:15:33 -0500

I've been trying to recode the squares.cpp C++ example in Java, using OpenCV 2.4.6, and I'm stuck with an error I don't understand:

OpenCV Error: Assertion failed (curve.checkVector(2) >= 0 && (curve.depth() == CV_32F || curve.depth() == CV_32S)) in arcLength, file /local/XXXX/libs/opencv-2.4.6/modules/imgproc/src/contours.cpp, line 1886

But when I check my curve, I get:

  • curve.checkVector(2) = 4

  • curve toString output: Mat [ 4 * 1 * CV_32SC2, isCont=true, isSubmat=false, nativeObj=0x7ffca453be90, dataAddr=0x7ffca4588720 ]

So I should be able to pass the assertion, but I fail.

Is CV_32SC2 different from CV_32S?

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"Is CV_32SC2 different from CV_32S?"

yes, CV_32SC2 has 2 channels, CV_32S has only 1

but your mat there has the type CV_32SC2 and the depth CV_32S

so, what did you feed in ?

  MatOfPoint2f m = new MatOfPoint2f(new Point(1,1),new Point(2,3),new Point(2,3));
  double d = Imgproc.arcLength(m, false);
      System.out.println("al " + d);
      // al 2.2360680103302
berak gravatar imageberak ( 2013-07-10 11:52:18 -0500 )edit

Thanks for the answer berak ! My mat is a MatOfPoint2f, in which I copy a MatOfPoint:

MatOfPoint contours = (previous code)

MatOfPoint2f contours2f = new MatOfPoint2f();


How can I copy the data in a MatOfPoint in a MatOfPoint2f and still keep type and depth coeherent?

Sodat gravatar imageSodat ( 2013-07-15 04:17:59 -0500 )edit

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answered 2013-07-15 09:48:05 -0500

Sodat gravatar image

Well, I seem to have solved the problem, though I'm not sure why...

By using:


instead of:


to copy the content of my MatOfPoint into my MatOfPoint2f, I don't fail the assertion anymore and my program is running fine (except it finds waaaay too many squares, but I'm trying to tweak it).

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ah, good. got a bit helpless, there ;)

berak gravatar imageberak ( 2013-07-15 09:59:51 -0500 )edit

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Asked: 2013-07-10 09:14:52 -0500

Seen: 1,941 times

Last updated: Jul 15 '13