STC ObservationLocation

[Rob Seaman]

Still catching up on my mail after SPIE.

On May 22, 2006, at 6:00 AM, Arnold Rots wrote:

> If you say BARY, it means you have applied a transformation.  And that
> transformation is based on model assumptions.
> There are a number of applications where it is crucial that users can
> undo that transformation (the obvious one being pulsar timing).

The question of making observatory location optional first came up  
with geocentric coordinates.  The point about GEO is that the  
location of the Earth is implicit in the epoch of the observation - a  
further correction to observatory locations "near" the Earth is  
likely unnecessary even if users later want to undo the light travel  
time.  While it is certainly desirable to convey as much context  
about an observation as possible, the question is whether it is  
necessary.

> And since it is a matter of just a single boiler plate line, it seems
> a minor inconvenience.

One person's minor inconvenience is another's major headache.  In  
particular, I've borrowed some comments from Doug from another thread:

>> I support use of STC to define reference frames in characterization
>> and elsewhere in VO, and probably for some things like region
>> descriptors, which STC is well able to deal with and which are not
>> currently addressed elsewhere, but not necessarily for something as
>> simple as a coordinate instance - there are many alternative ways
>> to represent something that simple.  Why can't a simple coordinate
>> instance in whatever representation be associated with an STC-defined
>> reference frame?

Usability issues are the alpha and omega of what will make or break  
STC.  If we didn't trust the underlying correctness of STC, we  
wouldn't be trying to use it in our various projects.  But users  
ultimately decide what is best, or even necessary, for their own  
projects.  I suspect that most of the core VOEvent group could  
correctly edit a brand new VOEvent packet by hand using vi or emacs -  
all elements and attributes except for STC, that is.  This makes us  
nervous.

Rob