Re: [boost] Is Boost.Astronomy feasible?

Subject: Re: [boost] Is Boost.Astronomy feasible?
From: Matthias Schabel (boost_at_[hidden])
Date: 2008-11-05 13:27:50

> Some examples on what calculations I think would be common are:
>
>  o sunrise, sunset, noon
>
>  o sun elevation, azimuth, declination
>
>  o length of the day
>
>  o phase of the moon, and whether the visible fraction is
>    increasing or not

Many of these types of calculations fall under the general domain of  
"astrometry" rather
than astronomy. I think this would be a very interesting addition to  
Boost, though, like
any non-trivial problem domain, it will be a challenge to find the  
appropriate balance
between feature-richness and excessive mission creep... Some of the  
functionality listed
here might be most sensible as an inclusion to Boost Date/Time...

>  o The sun may set/rise more than once during a day in polar regions,
>    or it may do neither.

Methods for getting all sunrises/sunsets within a given time window  
would make sense to me.

> o What is the definition for the length of the day if sunrise/sunset
>    occurs more than once during a day?

Again, a method for getting the interval between sunset and sunrise  
within a given time window
would sidestep this issue.

>  o Are separate methods needed for testing whether the given date
>    is of type "polar day" or "polar night" or "midnight sun"?
>    The definitions for the three seem to be a bit ambiguous. For
>    example, it is perfectly possible for the sun to be up at midnight
>    but still to set during the day, in which case you would have
>    "midnight sun" but not necessarily a "polar day", when the sun
>    shines 24h.

I would expect methods to query whether the sun is up or down at a  
given time/geographic location.
Special functionality for polar regions could be built on top of that...

> Many places refer to Meeus's work for the most accurate
> calculations.  The formulas have been ported to C++ in the form
> of the AA++ (astronomical algorithms) library. However, the
> library seems to be aimed for experts and there are no easy
> recipies for solving the common problems mentioned above.

Meeus' book is a good one. Another good source for astrometry code/ 
information is the Naval
Observatory Vector Astrometry Subroutines (NOVAS) library - this is  
more focused on astrometry,
but would be helpful if you wanted the library to support moonrise/ 
moonset or rise/set times for
planets.

>  o Would a boost::astronomy namespace as implied above be
>    a good addition to boost?

I would vote for boost::astrometry.

>  o Are there any experts out there who understand the subject
>    matter well enough to provide a robust implementation or
>    atleast guidance on the matter?

I have a fair amount of experience with astrometry software, but not  
tons of free time. I would be
happy to discuss interface issues and, where possible, to point you to  
existing implementations
that might be useful. Be forewarned : this is likely to become a much  
bigger undertaking than it
seems. To do all this correctly would require support for vector  
geometry, GIS, multiple time systems,
etc... I would recommend trying to add some of the basic sunrise/set  
functionality to Date-Time
first and see how that goes...

Matthias

>