Cuboid descriptor based on histogrammed gradient. Adaptation of Lowe's SIFT descriptor for cuboids. Creates a descriptor for an cuboid that is fairly robust to small perturbations of the cuboid. No histogramming (if histflag==-1) See "PCA-SIFT: A More Distinctive Representation for Local Image Descriptors" by Yan Ke for why this might be a good idea. Should not be called directly, instead use imagedesc. INPUTS I - MxNxT double array (cuboid) with most vals in range [-1,1] sigmas - n-element vector of spatial scales at which to look at gradient taus - n-element vector of temporal scales at which to look at gradient ch2params - see imagedesc_ch2desc ignGt - if 1 the temporal gradient is ignored OUTPUTS desc - 1xp feature vector, where p=n*prod(size(cuboid)) See also IMAGEDESC, IMAGEDESC_CH2DESC