Headers for GPS Information

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dirkterrell
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Headers for GPS Information

#1

Post by dirkterrell »

Robin, Dr. Qiu suggested I contact you about your discussion with him on putting GPS information in the FITS headers for cameras such as the QHY174-GPS. He said that you had concerns about getting the milli/microsecond information in a standard header item, but there should be no problem doing the standard DATE-OBS item as

DATE-OBS = '12:34:56.123456'

but we could certainly do a custom header if you felt that was best.

Dirk
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Re: Headers for GPS Information

#2

Post by admin »

Hi Dirk,

a standard DATE-OBS header seems to usually be in this format:

'2017-04-27T20:54:19'

with both the date and the time, leaving no space left for microsecond accuracy. I'm not sure if using a non-standard format for this header would be a good idea as it might confuse normal FITS reading software - this was why I thought a custom header might be a good idea.

Anyway, thanks for reminding me about this - it's easy to do and I will try to do it shortly.

cheers,

Robin
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Re: Headers for GPS Information

#3

Post by admin »

Ah, I just re-read my FITS header spec - maybe I can fit the extra digits in after all :)

Robin
dirkterrell
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Re: Headers for GPS Information

#4

Post by dirkterrell »

Yes, the FITS standard does allow for the decimal part of the seconds entry. Thanks for doing this. We are deploying 22 systems in a couple of weeks with QHY174-GPS cameras to observe occultations by 2014 MU69 (the encounter target for the New Horizons mission) and this will be a great benefit to us.

Dirk
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Re: Headers for GPS Information

#5

Post by admin »

Hi Dirk,

wow - what a cool thing to be able to help out with! I have just written the code now and I am hoping to make a new version available very shortly with this and a few other bug fixes in it.

Do you have any publicity about what you are doing? I'd love to be able to share this sort of thing on the SharpCap Facebook page!

cheers,

Robin
dirkterrell
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Re: Headers for GPS Information

#6

Post by dirkterrell »

We don't have anything up just yet. We've been so busy just trying to get such a big expedition pulled off on such short notice. (We are reducing HST observations made on Monday to get the final track for the shadow.) We'll be in South Africa and Argentina for an event on June 3 (UT) and in Argentina on July 17. Although I don't think we need the Pro version, I will order 22 licenses for the systems to show our support for your product and as a tangible "thank you" for adding the GPS time header stuff.

EDIT: I guess you don't get orders for multiple licenses at a time. :) Can you give me a way to do that without having to process 22 forms?

Dirk
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Re: Headers for GPS Information

#7

Post by admin »

Just for reference for anyone else looking for this feature - this is now implemented in build 3.0.3867.

Robin
jmgoldba
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Re: Headers for GPS Information

#8

Post by jmgoldba »

Fractional seconds are included in the FITS standard. For fractional second exposure times, any parser should expect them in the FITS header.

V 3.0 (18 Nov 2010) Sect. 4.4.2.1 states:

The decimal part of the seconds field is optional and may be arbitrarily long, so long as it is consistent with the rules for value formats of Sect. 4.2

Jesse
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Re: Headers for GPS Information

#9

Post by admin »

Thanks, yes, I found the right bit of the documentation in the end.

This issue is now fixed in the latest 3.0 build (timestamps down to the 100ns level), and there is also a button now to sync the PC time to the camera GPS time (requires running SharpCap as Administrator).

cheers,

Robin
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