# Standardized schema for proper motions in reference catalogs

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## Details

• Type: RFC
• Status: Implemented
• Resolution: Done
• Component/s:
• Labels:
None
• Location:
This RFC

## Description

We will need to apply proper motion corrections (when available) to our reference catalogs when generating astrometric solutions. We have no current standardized schema for these columns. Following suggestions from Paul Price following the lead of Pan-STARRS, I propose the following column names and units.

 pmRa -- Proper motion in the RA coordinate (mas/yr; float32) pmRaErr -- Error in proper motion in the RA coordinate (mas/yr; float32) pmDec -- Proper motion in the Declination coordinate (mas/yr; float32) pmDecErr -- Error in proper motion in the Declination coordinate (mas/yr; float32) epoch -- Mean epoch (TAI MJD for which the position needs no proper motion correction; float64) 

Note that the definitions above allow direct application of the proper motion correction by multiplying pmRa and pmDec by the difference in epoch in units of years. If the angular distance travelled is to be calculated a correction term to pmRa of cos(Dec) is required (or one could do the dot product in Cartesian 3-space).

If pmRaErr or pmDecErr are missing, zero error will be assumed. If any of pmRa, pmDec, or epoch are missing, no proper motion correction will be applied.

## Activity

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Colin Slater added a comment -

It would definitely be nice to have automatic support for reading Angles in different units, but in the absence of such a feature I won't object to storing radians.

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Colin Slater added a comment - It would definitely be nice to have automatic support for reading Angles in different units, but in the absence of such a feature I won't object to storing radians.
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Jim Bosch added a comment -

I took a look at support for different Angle units in afw.table, and documented my findings on DM-15174.  I do not have time to work on it now, but if Russell Owen feels comfortable taking that on (and it's consistent with what he's scheduled to do), it does sound like it may be worth doing before settling the schema question.

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Jim Bosch added a comment - I took a look at support for different Angle units in afw.table, and documented my findings on DM-15174 .  I do not have time to work on it now, but if Russell Owen feels comfortable taking that on (and it's consistent with what he's scheduled to do), it does sound like it may be worth doing before settling the schema question.  -
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Tim Jenness added a comment -

Are we close to adopting this again?

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Tim Jenness added a comment - Are we close to adopting this again?
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Jim Bosch added a comment -

I've reassigned this to Russell Owen.  I am okay with where we landed in the last few comments; I'll let him accept if he is as well.

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Jim Bosch added a comment - I've reassigned this to Russell Owen .  I am okay with where we landed in the last few comments; I'll let him accept if he is as well.
Hide
Russell Owen added a comment - - edited

Angle fields will be stored as radians, and proper motion as radians/year, for now. I filed RFC-502 suggesting we add support for persisting angles in other units.

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Russell Owen added a comment - - edited Adopted using Jim Bosch 's proposal . Angle fields will be stored as radians, and proper motion as radians/year, for now. I filed RFC-502 suggesting we add support for persisting angles in other units.

## People

• Assignee:
Russell Owen
Reporter:
Simon Krughoff
Watchers:
Christopher Waters, Colin Slater, Jim Bosch, John Parejko, Kian-Tat Lim, Paul Price, Robert Lupton, Russell Owen, Simon Krughoff, Tim Jenness