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Frank,

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[NavList 12731] Re: DeltaT fits
From: FrankReed---com
Date: 5 Apr 2010 05:05

you wrote :

QUOTE

For one arcsecond accuracy, you can probably cram all the data for the ecliptic latitudes and longitudes of the navigational planets, Sun, and Moon into 500 bytes. Maybe more, maybe less. This would give the daily positions for the outer planets, the hourly positions for the Moon, and positions at other intervals for Mars and Venus. Now since each data line has a fixed length, the search algorithm is nothing more than an array index. After that you're doing simple linear interpolation on the actual positions. That's LIGHTNING fast. For some of the celestial objects, the data stored this way may even be SMALLER than the long algorithms that you're currently using. So your application will be dramatically faster, and, if you're lucky, a little smaller.

UNQUOTE

Very interesting idea.

I am going to figure out in my (expected upcoming) spare time the quantity of computer data space required for each day.

In order to fully agree about such "starting conditions" before I undertake this research, may I summarize this "friendly challenge" of yours under the following form ?

- We are to define a daily array of numerical data in order to get a 1 arc second accuracy on the coordinates of the SUN + Moon + 4 Navigational Planets through linear interpolation.

- We start with standard data as available from any Modern and recent Numerical Integration ( let's take the best current one from JPL : their magnificent DE421 ) and we are authorised to "drop" some of their published figures and published results in order to save some computer space, as long as we fully guarantee 1" accuracy anyday anytime. We are using the data as they are published (i.e. I would assume the X,Y,Z Variables in the Ecliptic 2000.0 reference frame).

- The idea here is to best estimate the MINIMUM SIZE of the daily tabular data required to compute the apparent equatorial positions of these Bodies for any hour in the day to the guaranteed accuracy of 1". Such tabular data are to be put under the form of a FIXED SIZE (TBD) daily array so that the appropriate computer programs can just perform all required computations.

- The current research does NOT take in account anything else other than just the daily required data. A specific mention may be made to such any and all additionnal data required to process the daily Array data (Precession and Nutation series an example) but such additionnal data are NOT to be part of the just daily tally.

- The final and only result of this little exercise is just a "best estimate" of the MINIMUM SIZE of such daily array.

Are these assumptions fair enough to the point that they correctly represent your ideas as I can best understand and guess them from the lines hereabove ?

Thank you for your reply and for your Kind Attention.

Best Regards

Antoine M. "Kermit" Couëtte

PS : Any taker here ? Do not hesitate !!! (Peter ???) it will always be very interesting to compare results. Enjoy !!!

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