Multiscale Logic in direction.py

[AHorneffer]

O.K. the logic that decides when to do multiscale cleaning for the facet and when to switch on the wavelet module in pyBDSM is confusing, but not as crazy as I first thought it is...
The current logic is (assuming it isn't set to either True or False in the directions file):

1. If a source somewhere in the facet is larger than 6 arcmin, then multiscale cleaning for the facet is switched on.
2. If a source in the calibrator region is larger than 6 arcmin, then the wavelet module is switched on in pyBDSM. (*)
3. If the wavelet module in pyBDSM is switched on, then multiscale cleaning for the calibrator is switched on.
4. In facetimage_pipeline.parset it is hardcoded that the wavelet module is always used when imaging the full facet.

So shall we change steps 2 and 3 to:

• If a source in the calibrator region is larger than 2 arcmin, then the wavelet module is switched on in pyBDSM.
• If the wavelet module is switched on and a source in the calibrator region is larger than 6 arcmin, then multiscale cleaning for the calibrator is switched on.

P.S. (*) If there are no sources in the calibrator region, then Factor fails. Even if it is told not to selfcal this facet. Which prompted me to look into this. I'll commit a fix for that once I'm done with this issue.

P.P.S. This supersedes also #39

[darafferty]

Sounds good to me.

One related issue: I just added a low-res imaging step for patch-type directions (i.e., those that lie outside of the faceted region) that is only done when multiscale clean is activated for selfcal (it's intended to pick up extended emission missed during selfcal so that it's included in the subtraction). We might revisit this once the new logic is implemented, as it might be better to do the low-res image when there is a source larger than 2 arcmin rather than 6 arcmin (i.e., trigger on wavelet module activation rather than on multiscale clean).