Since the intensity values are resampled in the mapping from the raw space of the LI to the geometrically rectified space of the SI, the flag values must also be appropriately mapped into this new space. In order to map the flag values from raw space to the new geometric space, a ``resampling'' algorithm is clearly not desired as the flags have a very specific discrete meaning which must be maintained. The flag values need to be mapped to their new coordinates such that they retain their initial values, but also are appropriately assigned to additional locations in the remapped space in accordance to the distribution of intensities.
The residuals from integer coordinates are computed for the sample and line final floating-point geometric coordinates. These residuals are then evaluated in combination against a pre-defined threshold of 0.25. This threshold represents an ``in-between'' region which determines if the flags should be mapped to 1, 2, 3, or 4 pixels in the final geometric space.