Difference between `objects_ext.r_psfFluxNdata` and `objects.nrSources`

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#1

Hi Lasair team,
What is the difference between objects_ext.r_psfFluxNdata and objects.nrSources?
When I include these in a simple supernova query, I find:

  • Most of the objects have nrSources > 0
  • Some objects have nrSource == r_psfFluxNdata
  • Most objects have r_psfFluxNdata == 0

The schema browser says:
nrSources : ‘Number of r sources’
r_psfFluxNdata : ‘The number of r-band data points.’

So I guess a more fundamental question is, what is the difference between a source and a data point?

Thanks!
Chris

#2

The nrSources is made by Lasair, and pre-dates the Rubin attribute r_psfFluxNdata. I have no idea why the latter is often zero even when the number of r-band diaSources is not zero.