I'm implementing an algorithm that uses a so called 6-point interpolation, which I never heard before. In the article I'm reading it's described like this:
$\phi(p\Delta x, q\Delta y)=[q(q-1)/2] \phi_{0,-1}+[p(p-1)/2]\phi _{-1,0}$ $+(1-pq-p^2-q^2)\phi_{0,0}+[p(p-2q+1)/2]\phi_{1,0}+[q(q-2p+1)/2]\phi_{0,1}$ $+pq\phi_{1,1}+O(max(\Delta x,\Delta y)^2\phi_{0,0})$
Also, this image should clarify who are $q$ and $p$. http://i.minus.com/ibogDgHRRWKAVc.jpg
My implementation is running into some problems and I would like to at least exclude this obscure interpolation algorithm as a source of problems. Does anyone know how to obtain it?