If flt.zero_mask is set to one of " REF" , " MASK2" or " MASK3" then an NDF will be obtained using the specified ADAM parameter (REF, MASK2 or MASK3) and used as a user-defined mask. Setting flt.zero_mask to an integer value larger than zero has the same effect as setting it to " REF" . Setting it to an integer less than or equal to zero results in no external mask being used with the COM model. Note, using " REF" ensures that the mask and the output image of MAKEMAP are on the same pixel grid - using " MASK2" or " MASK3" does not provide this guarantee (it is then the users responsibility to ensure that the supplied masks are aligned with the output image in pixel coordinates). The pixels in the map that are to be included in filtering performed by the FLT model should be set to the bad value in the mask. All other pixels will be excluded from the filtering (i.e. they will be replaced by artifical data interpolated from the adjacent data). [0]