Detecting multiple squares within a square and extracting their coordinates

edit

again, i'm pretty sure, you won't need this, since you can easily infer the rectangle from the users position, and the position of the FloorMat , it's just plain maths after all

Rect floorMat(20,20, 600,600);  // let's assume, your mat is at 20,20, and it's 600 wide.   
Point user(344,523); // arbitrary user position

user -= floorMat.tl(); // translate to floorMat coords
cerr << user << endl;

int ix = int(user.x) / (floorMat.width / 3);  // get x,y square index
int iy = int(user.y) / (floorMat.height/ 3);    
cerr << ix << " " << iy << endl;

int rect_id = ix + iy *3 + 1; // +1, since you insist on starting to count at 1

cerr << "user is in square " << rect_id  << endl;

[324, 503]
1 2
user is in square 8

but here we go, let's try to detect the squares as well:

Mat ocv = imread("squares.jpg");
Mat image;
cvtColor(ocv,image,COLOR_BGR2GRAY);
threshold(image,image,20,255,1); // white on black required

vector<vector<Point>> contours;
findContours(image,contours,RETR_CCOMP,CHAIN_APPROX_SIMPLE);

vector<Rect> rects;
for ( int i=0; i<contours.size(); i++)
{
    double a = contourArea(contours[i]);
    if ( a > 5000 && a < 50000) // filter by size
    {
       drawContours(ocv,contours,i,Scalar(200,0,0));
       Rect r = boundingRect(contours[i]);
       rects.push_back(r);
    }
}

// for the fun of it, let's sort the rects l->r, t->d:
struct Less
{
    bool operator () (const Rect &a, const Rect &b) 
    {
        return (a.x + a.y*10000) < (b.x + b.y*10000);
    }
};

std::sort(rects.begin(),rects.end(), Less());

cerr << Mat(rects) << endl;

[6, 3, 89, 70;
 96, 3, 99, 70;
 196, 3, 87, 70;
 6, 74, 89, 91;
 96, 74, 99, 91;
 196, 74, 87, 91;
 6, 166, 89, 77;
 96, 166, 99, 77;
 196, 166, 87, 77]