Assertion Failed when trying to run projectPoints - c++

Question

I keep getting an assertion failed(0 <= i && i < (int)vv.size())in cv::_InputArray::getMat, in file matrix.cpp when trying to run projectPoints. I have checked everything I can think of but I can't work out what's wrong. My guess is something went wrong with the calibratecamera but I don't know how I would find out what is wrong exactly. Here is my code, thanks.
using namespace cv;
using namespace std;
std::vector<cv::Point3f> Generate3DPoints()
{
std::vector<cv::Point3f> points;
float x,y,z;
x=.5;y=.5;z=.5;
points.push_back(cv::Point3f(x,y,z));
x=0;y=0;z=0;
points.push_back(cv::Point3f(x,y,z));
x=-0;y=0;z=.5;
points.push_back(cv::Point3f(x,y,z));
x=0;y=.5;z=.5;
points.push_back(cv::Point3f(x,y,z));
x=0;y=-.5;z=0;
points.push_back(cv::Point3f(x,y,z));
x=.5;y=0;z=.5;
points.push_back(cv::Point3f(x,y,z));
x=.5;y=0;z=0;
points.push_back(cv::Point3f(x,y,z));
/*
for(unsigned int i = 0; i < points.size(); ++i)
{
std::cout << points[i] << std::endl;
}
*/
return points;
}
int main()
{
int numBoards = 4;
int numCornersHor = 6;
int numCornersVer = 9;
int numSquares = numCornersHor * numCornersVer;
Size board_sz = Size(numCornersHor, numCornersVer);
VideoCapture capture = VideoCapture(0);
vector<vector<Point3f>> object_points;
vector<vector<Point2f>> imagePoints;
vector<vector<Point2f>> image_points;
vector<Point3f> objectPoints1 = Generate3DPoints();
vector<Point2f> corners;
int successes=0;
Mat image;
Mat gray_image;
//capture >> image;
Sleep(1000);
capture.read(image);
imshow("Welcome", image);
vector<Point3f> obj;
for(int j=0;j<numSquares;j++)
obj.push_back(Point3f(j/numCornersHor, j%numCornersHor, 0.0f));
while(successes<numBoards)
{
cvtColor(image, gray_image, CV_BGR2GRAY);
bool found = findChessboardCorners(image, board_sz, corners, CV_CALIB_CB_ADAPTIVE_THRESH | CV_CALIB_CB_FILTER_QUADS);
if(found)
{
cornerSubPix(gray_image, corners, Size(11, 11), Size(-1, -1), TermCriteria(CV_TERMCRIT_EPS | CV_TERMCRIT_ITER, 30, 0.1));
drawChessboardCorners(gray_image, board_sz, corners, found);
cout << "SUCESS\n";
}
else
cout << "FAIL\n";
imshow("win1", image);
imshow("win2", gray_image);
capture.read(image);
image_points.push_back(corners);
object_points.push_back(obj);
printf("Snap stored!\n");
char continues;
cout << "Press c to continue\n";
cin >> continues;
successes++;
//if(successes>=numBoards)
// break;
}
Mat intrinsic = Mat(3, 3, CV_32FC1);
Mat distCoeffs;
vector<Mat> rvecs;
vector<Mat> tvecs;
intrinsic.ptr<float>(0)[0] = 1;
intrinsic.ptr<float>(1)[1] = 1;
calibrateCamera(object_points, image_points, image.size(), intrinsic, distCoeffs, rvecs, tvecs);
cout << "Done\n";
projectPoints(objectPoints1, rvecs, tvecs, intrinsic, distCoeffs, imagePoints);
cout << "done2";
return 0;
}

Answer 1

You are trying to pass rvecs and tvecs to the function projectPoints, which expects Mat and not vector<Mat>.
Basically, the calibrateCamera function estimates the intrinsics matrix and distortion coefficients of the camera using several images of a chessboard. The function also returns multiple versions of the extrinsics parameters (rotation+translation), one for each image you used. These extrinsic parameters are stored in rvecs and tvecs.
However, you want to project the 3D points in only one of these images, so you should choose what set of extrinsic parameters you want (i.e. rvecs[i] and tvecs[i], i corresponding to the image in which you want to project your object) and call projectPoints for these extrinsic parameters only, not the whole vectors<Mat>.