Standardising units and formats (and ref frames?) in transmission

[Anita M. S. Richards]

This is slightly off the main topic, but:

VOSpec - and VOScope and many other tools - do indeed manage coordinate 
conversions perfectly well, and certainly the STILTS library is capable of 
very high precision.

However, there is always the issue of whether the number of decimal places 
or significant figures used, is appropriate.  Ideally, that should be the 
same as, or to one more digit of precision, than the input data, at 
equivalent resolution (e.g. a sexagessimal position at milli-arcsec 
accuracy needs 8 decimal places in decimal degrees).  Numbers should also 
be exact; if 1 becomes 0.99999324 etc., and that is then subtracted from 
1.0000007, an exact value, errors will quickly creep in.  Excessive 
accuracy is also misleading.

Rounding errors (especially upwards) are not a disaster in search boxes, 
but they are if we start converting the actual data or even just 
performing operations on it.

How hard is it in the languages used to catch the input accuracy and 
format output data to the appropriate accuracy?

It is one of the things which confuses and annoys users, and teaches 
students bad habits!

thanks
a

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Dr. A.M.S. Richards, UK ARC Node/AstroGrid,
Jodrell Bank Centre for Astrophysics, Alan Turing Building, 
University of Manchester, M13 9PL
+44 (0)161 275 4124
and
MERLIN/VLBI National Facility, Jodrell Bank Observatory, 
Cheshire SK11 9DL, U.K. +44 (0)1477 571321 (tel) 571618 (fax)

"Socialism or barbarism?" Rosa Luxemburg (1915)

On Tue, 19 May 2009, Jesus Salgado wrote:

> Petr wrote:
>> The VOspec allows only degrees but if you enter the H:M:S representation
>> it makes strange numbers and performs the query of strange coordinates
>> (no complain).
>
> the strange coordinates you mention are in degrees, my friend!
>
> VOSpec admits the following string coordinates formats for RA:
>
> DD:MM:SS.SSS
> 18:36:56.336 is 18degrees, 36 minutes, 56.336 seconds (degrees are the
> default)(transformed to 19.538933333 degrees by VOSpec)
>
> DDh:MM:SS.SSS
> 18h:36:56.336 is 18hours, 36 minutes, 56.336 seconds,
> (transformed to 271.538933333333 degrees by VOSpec)
>
> DDd:MM:SS.SSS
> 18d:36:56.336 is 18degrees, 36 minutes, 56.336 seconds,
> (transform to 19.538933333 degrees by VOSpec)
>
> DDh:MMm:SS.SSSs
> of course, you could also add "m" and "s" to any of the previous
> formats, e.g., 18h:36m:56.336s
> (transformed to 271.538933333333 degrees by VOSpec)
>
> This is described in the VOSpec help pages
> http://esavo.esac.esa.int/VOSpecManual/gui.html#target
>
> (no complain) :)
>
> Best Regards,
> -- 
> Jesus J. SALGADO                       Jesus.Salgado at sciops.esa.int
>
> ESAC Science Archives Team
> European Space Astronomy Centre (ESAC)
> European Space Agency (ESA)
>
> European Space Agency/European Space Astronomy Centre
> P.O. Box 78
> 28691 Villanueva de la Canada                 Tel: +34 91 813 12 71
> Madrid - SPAIN                                Fax: +34 91 813 13 08
> -------------------------------------------------------------------
>
>
> ================================================================================================
> This message and any attachments are intended for the use of the addressee or addressees only. The
> unauthorised disclosure, use, dissemination or copying (either in whole or in part) of its content
> is prohibited. If you received this message in error, please delete it from your system and notify
> the sender. E-mails can be altered and their integrity cannot be guaranteed. ESA shall not be liable
> for any e-mail if modified.
> =================================================================================================
>
>