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| META TOPICPARENT |
name="ObsTAPdraftDiscussion" |
Use case 3.2 and 3.4 directly include constraints in radial velocities. It is a typical feature of some radio or interferometry cubes observing a single line to give measurements of fluxes for a given
spatio-radvel coordinate or spatio-redshift coordinate.
Discussion in Nara initiated by Arnold and Igor showed that most people consider the RadVel axis to be different from the spectral axis. The argument being that we are facing two non permutable quantities as long as we are not considering a single , isolated spectral line.
Upcoming version 2 of characterisation DM will add a new RadVel or Doppler axis. It would be perfectly possible to add a couple of optional fields allowing to search against "radial Velocity" bounds and resolution...
This is the minimum required to fulfill the use cases 3.2 and 3.4.
-- JuanDeDiosSantanderVela - 16 Mar 2011
In order to make a concrete proposal, I would propose the following fields:
-
vel_min: Minimum value of the line-of-sight velocity. Positive values indicate receding velocity.
- Mandatory: NO.
- datatype: adql:DOUBLE
- Can be
NULL: YES
- UCD: phys.veloc;stat.min
- Unit: m/s
- UType: to be discussed; could be
Char.VelocityAxis.Coverage.Bounds.Limits.Interval.LowLim
-
vel_max: Maximum value of the line-of-sight velocity. Positive values indicate receding velocity.
- Mandatory: NO.
- datatype: adql:DOUBLE
- Can be
NULL: YES
- UCD:
phys.veloc;stat.max
- Unit: m/s
- UType: to be discussed; could be
Char.VelocityAxis.Coverage.Bounds.Limits.Interval.HiLim
-
vel_resolution: Velocity difference average or reference bin size.
- Mandatory: NO.
- datatype: adql:DOUBLE
- Can be
NULL: YES
- UCD:
phys.veloc; spect.resolution
- Unit: m/s per bin
- UType: to be discussed; could be
Char.VelocityAxis.Coverage.Resolution.refVal
I do not like the term Radial Velocity, as it implicates a geometry in the object. Line-of-sight velocity (or plain Velocity, as in the proposal) seems better and cleaner to me. |
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> | Use Case 3.2 |
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> | Show me a list of all data that satisfies:
- DataType=Cube with 3 dimensions (see discussion on DataProduct)
- Axes includes Velocity
- Axes includes RA
- Axes includes DEC
- Velocity Resolution better than 50 km/s
- RA includes 16.000
- Dec includes +41.000
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> | An approximation might be: |
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> | select * from ivoa.obscore
where dataproduct_type = 'image-spectrum'
and vel_resolution < 50000
and (contains(s_region,point(16,+41))
or distance(point(s_ra,s_dec),point(16,+41)) < s_fov
) |
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<
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>
> | Condition 1 is dealt with by dataproduct_type field; condition 2 is dealt with by the fact that NULL vel_resolution fields will not contribute to the comparison; conditions 3 and 4 are taken care of at the same time as 6 and 7, by the contains or distance. The contains or distance is used to allow for services with non-precise regions, but that they still might have a chance of including the point. |
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