# LATISS UTC/TAI problems were fixed on 2021-02-12

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#### Details

• Type: Story
• Status: Done
• Resolution: Done
• Fix Version/s: None
• Component/s:
• Labels:
None
• Story Points:
0.5
• Team:
Architecture
• Urgent?:
No

#### Description

The obs_lsst LATISS metadata translator assumes that data after RASTART_IS_BAD is off by 37s, but in fact this was fixed on 2021-02-12. Please fix the metadata translator.

I'd do it myself, but I don't understand the comment

 # RASTART/DECSTART/RAEND/DECEND used wrong telescope location before this # 2020-02-01T00:00 we fixed the telescope location, but RASTART is still # in mount coordinates, so off by pointing model. RASTART_IS_BAD = Time("2020-05-01T00:00", format="isot", scale="utc") 

and would prefer you to clarify that the problem being fixed is not this one.

There is a more serious problem too, namely that the correction of c. 0.154167 is applied multiple times. The RAEND in the header is 130.211695172908, but:

 exposure.getMetadata().get("RAEND"), butler.get("raw_md", dataId).get("RAEND") (130.82836183957568, 130.36586183957567) 

#### Activity

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Tim Jenness added a comment -

Do I assume that after the 12th the RASTART/DECSTART are correct in the header and do not need any fixes?

I think for the double correction I'm going to have to finally bite the bullet and add a sentinel to the header indicating that it's been fixed. I've been wary of doing that because I didn't want to surprise people when something weird appears in their header. Maybe I should use something like HIERARCH ASTROMETADATA HEADER FIXED = TRUE.

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Tim Jenness added a comment - Do I assume that after the 12th the RASTART/DECSTART are correct in the header and do not need any fixes? I think for the double correction I'm going to have to finally bite the bullet and add a sentinel to the header indicating that it's been fixed. I've been wary of doing that because I didn't want to surprise people when something weird appears in their header. Maybe I should use something like HIERARCH ASTROMETADATA HEADER FIXED = TRUE .
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Tim Jenness added a comment -

To clarify the situation inherited from DM-28783:

• At 2021-02-11T1845Z the headers were decimal degrees but had a 37s error in RASTART.
• At 2021-02-12T0000Z the 37s was fixed.

So it was less than 6 hours of data where the 37s error was a real problem.

Show
Tim Jenness added a comment - To clarify the situation inherited from DM-28783 : At 2021-02-11T1845Z the headers were decimal degrees but had a 37s error in RASTART. At 2021-02-12T0000Z the 37s was fixed. So it was less than 6 hours of data where the 37s error was a real problem.
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Tim Jenness added a comment -

Furthermore, the RASTART test will fail because even as I was fixing the translator to deal with the problem of the time offset the problem had been fixed but I had not been informed. This means that the data I was looking at was already correct. The reason I thought it needed fixing was that this did make the number closer to the target RA (260.178 [fixed] vs 260.181 [demand] vs 260.024 [header]).

Show
Tim Jenness added a comment - Furthermore, the RASTART test will fail because even as I was fixing the translator to deal with the problem of the time offset the problem had been fixed but I had not been informed. This means that the data I was looking at was already correct. The reason I thought it needed fixing was that this did make the number closer to the target RA (260.178 [fixed] vs 260.181 [demand] vs 260.024 [header] ).
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Tim Jenness added a comment -

I took your fix and sorted out the test.

I'm going to do the double fixup fix in a different ticket because that can be done entirely inside astro_metadata_translator.

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Tim Jenness added a comment - I took your fix and sorted out the test. I'm going to do the double fixup fix in a different ticket because that can be done entirely inside astro_metadata_translator.
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Robert Lupton added a comment -

Looks fine

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Robert Lupton added a comment - Looks fine

#### People

Assignee:
Tim Jenness
Reporter:
Robert Lupton
Reviewers:
Robert Lupton
Watchers:
Michael Reuter, Robert Lupton, Tim Jenness