Setting the flt.zero_snr parameter will prevent samples contributing to the FLT model if they fall within map pixels that have SNR values greater than flt.zero_snr. A flt.zero_snr value of zero means no SNR mask is used. See also parameter "flt.zero_snr_ffclean" .

Note, the SNR values are only available once a map has been created, and so using this parameter results in no FLT masking on the first iteration. Consequently the map at the end of the first iteration will have deep rings around bright sources, since no FLT masking was done. Normally, these rings would polute the AST model derived from the map, and thus polute the residuals on the next iteration, resulting in the rings remaining in later maps. To avoid this, parameter "ast.skip" can be set to a positive value. This causes the AST model to be skipped (i.e. no AST signal is subtracted from the residuals) for the first " ast.skip" iterations. This means that a good FLT mask can be formed from these initial iterations before any AST model is calculated and used. [0.0]

MAKEMAP, CALCQU