kernel - Kernel operators

• gausskernel - Compute a 1D or 2D Gaussian filter.
• dirgausskernel - Compute an oriented Gaussian kernel.
• hourglasskernel - Compute an oriented non-linear spatial hourglass filter.
• euclidkernel - Create a kernel spatially weighted with the euclidean distance.
• local3x3kernel - Compute local kernels defined by zones and levels.
• neiposkernel - Create the kernel containing the indices and subscript positions of the grid pixels of a given square window.