[Nexus] item discussed now

[Eugen Wintersberger]

Hi folks
  though that I did not attend todays telecon - I would like to make a
remark here as I am currently working with transformations quite a lot
while designing the NeXus layout for several of our beamlines at PETRA
III.

On Wed, 2015-02-18 at 07:36 -0500, Herbert J. Bernstein wrote: 
> As per our discussion on the hangout today, please note the following
> clarification:
> 
> When specifying the position of a component with a depends_on field,
> the specific point in the component being positioned will either be
> the center of the first pixel for a detector 

This is quite fine. One can mange this as every 2D detector has
something like a first pixel. 

> or the center of the
> component for components not having an equivalent to a "first pixel".

This is a bit more complex. What would be the "center" of a component. 
The entire situation remains me a bit on 3D modelling software which
follows a composite geometry approach. All of their 3D primitives have a
well defined center. However, one has to consult the manual of the
software package to learn where the center for a particular primitive is
(different software packages can make different choices where to place
the center for a particular primitive). At least all software packages I
kow use this "center" as the origin for the primitive local coordinate
frame. In my opinion this is what we are missing - a center for each
"component" onto which we can bind the origin of the local coordinate
frame.  

The question that arises for me is: is it possible to define such a
center for our base classes (for those who can be used along with
transformations) in a generic manner (in a way independent of the
particular mechanical construction)?

BTW. This discussion does not render transformations useless. From my
experience at PETRA III they have already proven quite useful when
describing the dependencies of axes. However, I guess this discussion
can greatly improve the usability of transformations.  

regards
  Eugen

> 
> On Wed, Feb 18, 2015 at 7:29 AM, Pete Jemian <prjemian at gmail.com> wrote:
> >
> > use this URL for the transformations
> > http://download.nexusformat.org/doc/html/design.html#coordinate-transformations
> >
> > On 2/18/2015 6:10 AM, Pete Jemian wrote:
> >>
> >> https://github.com/nexusformat/definitions/blob/depends_on/nxdl.xsd
> >>
> >>
> >> On 2/18/2015 6:05 AM, Pete Jemian wrote:
> >>>
> >>>
> >>>
> >>> https://github.com/nexusformat/definitions/issues/273#issuecomment-74158201
> >>>
> >>>
> >>
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