PRANCS is a novel approach to NCS operator determination that does not use any sequence information or heavy atom positions. In this approach, the main assumption is that regions related by NCS tend to have similar density patterns as opposed to regions unrelated by NCS. The similarity between density patterns is measured using the local density correlation metric. The density correlation calculations between all the regions in an electron density map are time and CPU intensive. In order to reduce the computational time rotation invariant features based on electron density are used to describe regions of the map. The similarity between features is used to filter out very dissimilar regions and the density correlations are computed only between regions that have very similar feature vectors.