<div dir="ltr"><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Sexagesimal values are strings that can be further parsed/interpreted so that falls right into what xtype is for. It would be two closely related xtype values.</div><div class="gmail_default" style="font-size:small">I say "strings" because of the colons in the serialization... they could in principle be {double,3,ra} and {double,3,dec} (eg) if that serialization was potentially useful/acceptable. #scope-creep</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">The other alternative, which is always a possibility when thinking about xtypes, is to introduce two new datatype(s) in VOTable, but in the past there was reluctance to introduce non-primitive types there. Certainly adding xtypes is more backwards-compat friendly than new datatypes.<br></div><div class="gmail_default" style="font-size:small"><br clear="all"></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div>--<br></div><div>Patrick Dowler<br></div>Canadian Astronomy Data Centre<br></div>Victoria, BC, Canada<br></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 10 Mar 2022 at 09:17, Mark Taylor <<a href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear Semantics and DAL,<br>
<br>
following the report I gave on VOUnit usage in the VO at the last interop<br>
(<a href="https://wiki.ivoa.net/internal/IVOA/InterOpNov2021Ops/uuc.pdf" rel="noreferrer" target="_blank">https://wiki.ivoa.net/internal/IVOA/InterOpNov2021Ops/uuc.pdf</a>)<br>
Gilles Landais at CDS has done a good job of tidying up the units<br>
reported by VizieR to conform to the VOUnit standard (the results are<br>
not yet visible in the public VizieR service).<br>
<br>
But one issue that remains is how to flag up sexagesimal quantities,<br>
which are currently marked up like this:<br>
<br>
<FIELD name="RAJ2000" ucd="pos.eq.ra;meta.main" ref="J2000" <br>
datatype="char" arraysize="12" unit="'h:m:s'"><br>
<FIELD name="DEJ2000" ucd="pos.eq.dec;meta.main" ref="J2000" <br>
datatype="char" arraysize="13" unit="'d:m:s'"><br>
<br>
The unit, by long VizieR tradition, is quoted as 'h:m:s' or 'd:m:s'<br>
(including the single quotes), which is probably recognised as an<br>
ad hoc indication by quite a bit of client code out there. <br>
However this is not legal VOUnit syntax, and they're not really units <br>
anyway since the columns they apply to are not numeric, but it's not <br>
obvious how to indicate sexagesimal content of columns in VOTable metadata.<br>
You can infer it by noticing ucd="pos.eq.*" and datatype="char",<br>
but it seems like there ought to be a more explicit way to do this, <br>
especially considering how common this case is in the tables we deal <br>
with.<br>
<br>
So: what would be the VO-compliant way for CDS to proceed here?<br>
(note I'm not claiming that they are going to follow any such advice,<br>
that's for Gilles to decide). Do we just leave consumers to make a<br>
good guess based on UCD and datatype? Could it be a job for DALI/xtype?<br>
Something else?<br>
<br>
Mark<br>
<br>
--<br>
Mark Taylor Astronomical Programmer Physics, Bristol University, UK<br>
<a href="mailto:m.b.taylor@bristol.ac.uk" target="_blank">m.b.taylor@bristol.ac.uk</a> <a href="http://www.star.bristol.ac.uk/~mbt/" rel="noreferrer" target="_blank">http://www.star.bristol.ac.uk/~mbt/</a><br>
</blockquote></div>