In OpenCV what is CvMatND structure used for?

Question

I've noticed in the O'rielly book that when using histograms it refers to a cvMatND data structure. However, the book does not explain what this data structure is used for and how its different then cvMat. Can someone please explain this to me? Thank you.

Answer 1

Maybe this helps: http://opencv.willowgarage.com/documentation/python/basic_structures.html

Answer 2

cvMat is two-dimensional (multi-channel) array, i.e., a matrix.
cvMatND is an n-dimensional (multi-channel) array.

See the Basic Structures section in the CXCORE reference manual.

Update:

A histogram can be computed in arbitrary dimensions, therefore the definition of the CvHistogram structure uses CvMatND to store multidimensional histograms to a dense multidimensional array structure.

typedef struct CvHistogram
{
    int      type;
    CvArr* bins;
    float thresh[CV_MAX_DIM][2]; // for uniform histograms
    float** thresh2;             // for nonuniform histograms
    CvMatND mat;                 // embedded matrix header
                                 // for array histograms
}
CvHistogram;