Re: Just what is a Dec Arc model?

Howard Hedlund

This looks like a great thread for some clarification and clean-up of our language.  Consistent  language is vital to avoiding confusion.
  • The theory behind the Dec-arc approach is that it concentrates the data used to model along the natural arc in declination that the object appears to trace across the sky.
  • The Dec-arc approach suffers the same naming pitfall as the all-sky approach. The biggest offender is the word *model*.
  • A model is a predictive set of algorithms that take existing real data, and apply that data to predict future outcomes.  Numerous algorithms are employed to optimize results.
  • To acquire that data, we employ a technique we call *mapping*.  The better the data we map, the better the predictive value.
  • We, as users, never see the model.  We don't create the model.  We do, however, collect the data that the model will employ, and we do this by *mapping* points in the sky.
  • APPM stands for Astro-Physics Point Mapper.  APPM is simply the data collector for APCC.  APPM allows you to strategize your data collection to best serve your individual needs. 
  • Our observing and imaging goals determine the best approach to mapping and using the data.
    • Are you worried about pointing?  Create an all-sky mapping in APPM and then go ahead and bounce from target to target.  
    • Are you tracking just one or two objects over the course of a night?  Then use APPM to map the relevant individual arcs in declination that you will be following as you track.
  • All we do is to map.  What APCC does is to take our mapped data and build a model.

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