myselfesteem myselfesteem - 1 month ago 24
C++ Question

Create Mat from vector<point2f>

I am extremely new to computer vision and the opencv library.

I've done some googling around to try to find how to make a new image from a vector of Point2fs and haven't found any examples that work. I've seen

to
Mat
but when I use those examples I always get errors.

I'm working from this example and any help would be appreciated.

Code: I pass in occludedSquare.

resize(occludedSquare, occludedSquare, Size(0, 0), 0.5, 0.5);

Mat occludedSquare8u;
cvtColor(occludedSquare, occludedSquare8u, CV_BGR2GRAY);

//convert to a binary image. pixel values greater than 200 turn to white. otherwize black
Mat thresh;
threshold(occludedSquare8u, thresh, 170.0, 255.0, THRESH_BINARY);



GaussianBlur(thresh, thresh, Size(7, 7), 2.0, 2.0);

//Do edge detection
Mat edges;
Canny(thresh, edges, 45.0, 160.0, 3);

//Do straight line detection
vector<Vec2f> lines;
HoughLines( edges, lines, 1.5, CV_PI/180, 50, 0, 0 );

//imshow("thresholded", edges);


cout << "Detected " << lines.size() << " lines." << endl;

// compute the intersection from the lines detected...
vector<Point2f> intersections;
for( size_t i = 0; i < lines.size(); i++ )
{
for(size_t j = 0; j < lines.size(); j++)
{
Vec2f line1 = lines[i];
Vec2f line2 = lines[j];
if(acceptLinePair(line1, line2, CV_PI / 32))
{
Point2f intersection = computeIntersect(line1, line2);
intersections.push_back(intersection);
}
}

}

if(intersections.size() > 0)
{
vector<Point2f>::iterator i;
for(i = intersections.begin(); i != intersections.end(); ++i)
{
cout << "Intersection is " << i->x << ", " << i->y << endl;
circle(occludedSquare8u, *i, 1, Scalar(0, 255, 0), 3);
}
}

//Make new matrix bounded by the intersections
...
imshow("localized", localized);

Answer

Should be as simple as

std::vector<cv::Point2f> points;
cv::Mat image(points);
//or
cv::Mat image = cv::Mat(points) 

The probably confusion is that a cv::Mat is an image width*height*number of channels but it also a mathematical matrix , rows*columns*other dimension.

If you make a Mat from a vector of 'n' 2D points it will create a 2 column by 'n' rows matrix. You are passing this to a function which expects an image.

If you just have a scattered set of 2D points and want to display them as an image you need to make an empty cv::Mat of large enough size (whatever your maximum x,y point is) and then draw the dots using the drawing functions http://docs.opencv.org/doc/tutorials/core/basic_geometric_drawing/basic_geometric_drawing.html

If you just want to set the pixel values at those point coordinates search SO for opencv setting pixel values, there are lots of answers

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