The NDDI operator algorithm computes the Normalized Difference Drought Index from a given product.

The NDDI results from the following equation:

NDDI = (((N - R) / (N + R)) - ((G - N) / (G + N))) / (((N - R) / (N + R)) + ((G - N) / (G + N)))

, where:

The bands are:

- G is the Green band
- R is the Red band
- N is the NIR band

Also the processor computes an additional flags band called 'nddi_flags' with the following bit coding:

Bit Position	Description
Bit 0	The computed value for NDDI is NAN or is Infinite
Bit 1	The computed value for NDDI is less than -1 (minus one)
Bit 2	The computed value for NDDI is greater than 1 (one)