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ivoa-std / ObsCoreExtensionForRadioData

ObsCore model extension for radio data
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s_maximum_angular_scale #54

Open alle-ira opened 6 months ago

alle-ira commented 6 months ago

in Sect. 4.1 the definition of s_maximum_angular_scale should be corrected. The parameter l is the minimum distance between two antennas/stations in the array (instead of the typical smallest distance in the uv plane), expressed in meters.

Bonnarel commented 6 months ago

Can you explain why the smallest distance doesn't make sense here ?

kettenis commented 6 months ago

@alle-ira It really is a distance in the uv plane that sets the maximum angular scale instead of the physical distance between antennas. A more correct phrasing would perhaps be that the maximum angular scale is set by the track in the uv-plane that is closest to the origin of the uv plane. But there are all kinds of subtleties; those tracks are ellepsoids, so do you take the minor or major axis, or some sort of average? And if you only have one short baseline that is some sort of outlier, does that really set a useful maximum angular scale? Perhaps I'm worrying too much about the VLBI case, but I really don't think we can provide an exact formula in the standard here.

alle-ira commented 6 months ago

We were focusing on what seems to be a typo in the definition written in Sect 4.1 (and also in Sect. 3.4 regarding s_resolution). If $\lambda$/l is used, then l should be the minimum distance between two antennas/stations in the array.