Assertion Failed <0 <= i && i < <int>vv.size<>> in unknown function, file src\matrix.cpp, line 912

Question

First of all, i'm to new to the site (but i read and cacth info from it since a long time yet :D) so sorry if i'll make some error in structuring the question...and most important, i'm new to programming (ok not new, but i started 6 months ago).. anyway, this is the code (the interested part):

extern DWORD miothread3 (LPDWORD lpdwParam)
{

Mat epsilon(dest);
Mat finale;
Mat *super;
int ratio = 3;
int lowThreshold;
int kernel_size = 3;
int i = 0;
CvConvexityDefect convessione;
vector<vector<Point> > contorni;
vector<Vec4i> gerarchia;
Mat hull;

while(1)
{
    Canny(epsilon, finale, lowThreshold, lowThreshold*ratio, kernel_size );
    findContours(finale, contorni, CV_RETR_LIST, CV_CHAIN_APPROX_NONE);
    convexHull(contorni, hull);
}
return 0;
}

when i run it, i got the assertion in title ("Assertion Failed <0 <= i && i < <int>vv.size<>> in unknown function, file src\\matrix.cpp, line 912") and if i comment the line of convexHull(contorni, hull); it does work... i really cannot figure out what's the problem...so, if someone could help, would be lovable!:)

thank you in advance, best regards.

Answer 1

That assertion is due to the code trying to access an invalid index of the contorni object (see line 937 in the current source code) . I suspect this is ultimately due to passing an invalid contorni object into the convexHull() function, perhaps an empty vector. Normally, I would expect the function to check and reject invalid input although I don't know enough about openCV to know whether the function it requires valid input or not (the documentation doesn't mention it one way or the other).

To avoid this error I would explicitly check the input to convexHull() and/or findContours() to ensure it is valid and abort or do something appropriate if it isn't.