Setting the com.zero_snr parameter will exclude samples from the COM estimate that fall within map pixels with SNR values greater than com.zero_snr. A com.zero_snr value of zero means no SNR mask is used. See also parameter "com.zero_snr_ffclean" .

Note, the SNR values are only available once a map has been created, and so using this parameter results in no COM masking on the first iteration. Consequently the map at the end of the first iteration will have a bowl around any bright sources, since no COM 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 bowls 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 COM mask can be formed from these initial iterations before any AST model is calculated and used. [0.0]

MAKEMAP, CALCQU