The FLT.FILT_EDGE_LARGESCALE_LAST makemap configuration parameter allows you to create a map in which the background regions (i.e. the regions zeroed out by the AST mask) are filtered on a shorter scale than the source regions, thus producing a pleasingly flat background without removing structure from the source regions.
However, when using this option care needs to be taken when interpreting the variances stored with the map. Setting FLT.FILT_EDGE_LARGESCALE_LAST causes the filter size to be changed on the last iteration. Whilst this does not affect the data values in the source regions much (since the source signal has been extracted into a separate model by the time the final iteration occurs), it does affect the variances. This is because the variances are formed from the time-stream residuals that are left after removal of the astronomical signal estimated on the penultimate iteration, and all these residuals - no matter where they are on the sky - are filtered using the smaller filter size given by FLT.FILT_EDGE_LARGESCALE_LAST.
The upshot of all this is that the basic scheme described above results in artificially low variances in the source regions. To avoid this, a change was introduced into SMURF on 13th February so that now, if the FLT.FILT_EDGE_LARGESCALE_LAST parameter is set, the variances stored in the map are the ones generated on the penultimate iteration (that is, the final iteration that used the basic filter size rather than the special last-iteration filter size). This should give more realistic variances for the source regions, but at the cost of unrealistically high variances in the background regions.
However, when using this option care needs to be taken when interpreting the variances stored with the map. Setting FLT.FILT_EDGE_LARGESCALE_LAST causes the filter size to be changed on the last iteration. Whilst this does not affect the data values in the source regions much (since the source signal has been extracted into a separate model by the time the final iteration occurs), it does affect the variances. This is because the variances are formed from the time-stream residuals that are left after removal of the astronomical signal estimated on the penultimate iteration, and all these residuals - no matter where they are on the sky - are filtered using the smaller filter size given by FLT.FILT_EDGE_LARGESCALE_LAST.
The upshot of all this is that the basic scheme described above results in artificially low variances in the source regions. To avoid this, a change was introduced into SMURF on 13th February so that now, if the FLT.FILT_EDGE_LARGESCALE_LAST parameter is set, the variances stored in the map are the ones generated on the penultimate iteration (that is, the final iteration that used the basic filter size rather than the special last-iteration filter size). This should give more realistic variances for the source regions, but at the cost of unrealistically high variances in the background regions.
