DiscussionOnVOUnits < IVOA

---+ Discussion on <nop>VOUnits

This page is created to discuss the [[http://www.ivoa.net/internal/IVOA/UnitsDesc/WD-VOUnits-1.0-20111216.pdf][VOUnits 1.0 document]], and to find a consensus on undecided issues, by listing pros and cons on each item. For each item on the page, various options are presented, and the community is encouraged to express opinions in order to reach a consensus, by appending your wikiname to the preferred option, and/or commenting.


---++ Symbols

---+++ Electric resistance 
The IAU recommends to use the upper-case greek letter Omega, but this is not allowed with the adopted character set for VOUnits. OGIP uses ohm (lower-case o), while <nop>StdCats and FITS recommend Ohm (upper-case o).

The upper-case version seems more appropriate (refers to the name of Georg Simon Ohm).

Options for VOUnits :
   1. Accept both ohm and Ohm. pro: remains compatible with all current use. con: adds complexity to parsing.
   1. Only allow Ohm. pro: easier parsing. con: translation needed for OGIP (but is this unit really used in astronomy?). 

*Discussion:*

---+++ Micro-arcseconds
This is not yet widely used, but it will probably be the case
with future astrometric missions like GAIA.
We have arcsec, and mas (while IAU recommends nanoradians nrad). 
Options for VOUnits :
   1. Follow only IAU style: nrad, prad...
   1. uas
   1. uarcsec

*Discussion:*

---+++ Celcius
Do we keep a degC symbol?

*Discussion:*

---+++ Dropped deprecated symbols (Table 5)
Any objections to removing these from the standard ?
dyn, cal, bar, atm, Gal, eotvos, gamma, oersted

*Discussion:*

---+++ Other symbols (Table 6)
Is it OK to reuse the FITS 2010 notations?

*Discussion:*

-----

---++ Special cases

---+++ Quantity with no unit

For example a character string or a dimensionless ratio.
We suggest to use an empty string. Other possibilities are
one or 3 dashes, or blanks.

*Discussion:*

---+++ Percent
This means a factor 0.01, with no unit. Do we allow "%"?

*Discussion:*

---+++ Unknown unit
What to do when we know the unit is not known? 
   1. Use a question mark: ?
   1. Use an empty string
   1. Other notation?

*Discussion:*

-----

---++ Mathematic expressions

Any objections to following the FITS guidelines?

Regrets that VOUnits don't include trigonometric functions?

*Discussion:*

-----

---++ AOB ?








<br/>
<!--
      * Set ALLOWTOPICRENAME = %MAINWEB%.TWikiAdminGroup
-->
This topic: IVOA > WebHome > IvoaDataModel > UnitsDesc > DiscussionOnVOUnits
Topic revision: r1 - 2011-12-16 - SebastienDerriere