Equivalent of c++ std::vector<cv::Vec6f> in java with javacv?

[Luca96]

Hi, I'm trying to use the Subdiv2D (from opencv_imgproc) class to perform the Delaunay triangulation.
I need to call the getTriangleList(FloatPointer) method, but it need a FloatPointer object as parameter.
From Opencv documentation, the method getTriangleList need a std::vector<cv::Vec6f> as parameter.
How can i achieve the same in java with javacv?

[saudet]

Would you have some sample code in C++ that you are trying to translate to Java?

[Luca96]

Hi @saudet , here is the code:

cv::Subdiv2D subdiv(rect); //rect is a cv::Rect

// Insert points into subdiv (points is a vector<cv::Point2f>)
for (size_t i = 0; i < points.size(); ++i)
       subdiv.insert(points[i]);

//getting the triangles from subdiv
vector<cv::Vec6f> triangleList;
subdiv.getTriangleList(triangleList);

[saudet]

Something like this should work then:

FloatPointer triangleList = new FloatPointer(null);
subdiv.getTriangleList(triangleList);
int n = triangleList.limit() / 6;
...

Could you give it a try?

[Luca96]

It seems to work, here is my code:

FloatBuffer buffer = null;
FloatPointer triangleList = new FloatPointer(buffer); 

subdiv2D.getTriangleList(triangleList);
long n = triangleList.limit() * 6;

for (int i = 0; i < n; i++)
      float f = triangleList.get(i); //points coordinate

I only changed few things like:

FloatPointer triangleList = new FloatPointer(null);
//to
FloatPointer triangleList = new FloatPointer(buffer); 
//to avoid: Cannot resolve constructor: FloatPointer(null); ERROR

//and

int n = triangleList.limit() / 6; //number of triangles
//to
long n = triangleList.limit() * 6; //all points coordinate (that is what i need :D )

So, thanks again @saudet for your help!!

[saudet]

Hum, ok, so the number of points doesn't come out right with that hack. We'll need to do something about that. Thanks for reporting!

[Luca96]

Thank you sir!
But i notice that i can do strange things like this:

 //really strange, upper bound should not exceed triangleList.limit() * 6
long n = triangleList.limit() * 6 * 10; 

//getting coordinate
for (int i = 0; i < n; i += 2) { 
      float x = triangleList.get(i);
      float y = triangleList.get(i + 1);
}

When i >= 0 and i < triangleList.limit() * 6 i get the right coordinate with some strange value like this: (x: -1800.00, y: -1800.00)

But when i >= triangleList.limit() * 6 and i < n , i would expect an error instead i get other values (close to 0) like: (x: 0.000133, y: 0.000145), (x: -0.000192, y: 0.000035)), ... and a lot of zeroes (x: 0.00, y: 0.00)

Note that the right x and y are between 100 and 500.

Is this normal or caused by some memory inconsistencies or some algorithmic bugs of cv::Subdiv2D?

[saudet]

FloatPointer doesn't do bounds checking, that's normal.

[saudet]

This has now been fixed with JavaCV 1.5, which provides a nice Vec6fVector wrapper class for this. Thanks for reporting!