opencv - Freak Descriptor Row type -

i have following code:

//newimg mat of image , orderedkeypoint result fast cv::freak extractor; cv::mat querydescriptors; extractor.compute(newimg, orderedkeypoint, querydescriptors); 

i trying access individual freak descriptors using querydescriptors.at< ???>(r,0) r arbitrary valid row value not sure of type. documentation states descriptor, of type mat or double or else? best way of doing it?

cv::mat descriptor2 = querydescriptors.at<cv::mat>(2,0); 

i able reconstruct querydescriptors (mat of descriptors) individual descriptors taking them , putting them in row values of cv::mat, ex:

querydescriptors.at<cv::mat>(2,0) = descriptor2; 

any or insight appreciated,

isaac

the freak descriptor uchar mat 64 cols , numkeypoints rows.

so, element of it:

uchar elm = descriptor.at<uchar>(row,col); 

where row keypoint id, , col element id.