Invalid Arguments In Convexhull Android Ndk And Opencv

I have this C++ OpenCV code in my jni folder of android application hello-jni.cpp. I just want to find and draw convexhull but cause of hull[i] the convexhull method generate an er

Solution 1:

When you initialize hull

vector<vector<Point> > contours;
vector<vector<Point> > hull(contours.size());

hull size is 0, since contours size is 0. So when you access hull[i] you are accessing out of bounds.

Declare hull after findContours:

findContours(threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0));
 vector<vector<Point> > hull(contours.size());

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You can also simply call convexHull as:

 convexHull(contours[i], hull[i]);

since 3rd argument orientation is false by default, and 4th argument returnPoints is ignored when 2nd argument is a std::vector.

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thresh value is ignored when you use THRESH_OTSU.

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UPDATE

It seems that there are some problems with Android NDK. A simple workaround is:

• disable the error for invalid arguments, or
• use the following

Code:

Mat mHull;
convexHull(Mat(contours[i]), mHull, false, true);
hull[i].assign(mHull.begin<Point>(), mHull.end<Point>());