Start /Mid /End selection for fits file & additional header info

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Mind's Eye
Posts: 6
Joined: Wed Nov 20, 2019 1:59 pm

Start /Mid /End selection for fits file & additional header info

#1

Post by Mind's Eye »

Hi All,
Can there be a selection for setting the time in the Fits file headers?
Doing astrometry or anything timed requires being able to set time of the exposure. An example would be mid frame for measuring purposes. I see that sharpcap uses the start time now.
Additionally can more info be included in the header such as observatory name, observer name Ect. as with other fits files.

Thanks
Terry
Minds Eye Observatory

SIMPLE = T / C# FITS: 09/28/2021 20:27:59
BITPIX = 16
NAXIS = 2 / Dimensionality
NAXIS1 = 1304
NAXIS2 = 976
BLKLEVEL= 0 /
GAIN = 300 /
EQUINOX = 2021.74316939891 /
OBJCTDEC= '+42 18 40.000' /
OBJCTRA = '21 10 38.000' /
DEC = 42.3113888888889 /
RA = 317.658333333333 /
DATE-OBS= '2021-09-29T00:27:56.2052853' / System Clock:Est. Frame Start
SWCREATE= 'SharpCap' / v3.2.6482.0, 32 bit
BAYOFFY = 1 /
BAYOFFX = 1 /
COLORTYP= 'BGGR ' / NOTE: Use GRBG on some software (eg PixInsight)
OBJECT = '2003QQ47 143649' /
CCD-TEMP= 31.2 /
YBINNING= 1 /
XBINNING= 1 /
YPIXSZ = 3.75 /
XPIXSZ = 3.75 /
EXPTIME = 3 /
BSCALE = 1 /
BZERO = 32768 /
EXTEND = T / Extensions are permitted
BAYERPAT= 'BGGR ' / NOTE: Use GRBG on some software (eg PixInsight)
INSTRUME= 'ZWO ASI224MC' /


Example from another source:
SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 1304 / length of data axis 1
NAXIS2 = 976 / length of data axis 2
BZERO = 32768 / offset data range to that of unsigned short
BSCALE = 1 / default scaling factor
ROWORDER= 'BOTTOM-UP' / Order of the rows in image array
EXPTIME = 0.5 / [s] Total Exposure Time
PIXSIZE1= 3 / [um] Pixel Size X, binned
PIXSIZE2= 3 / [um] Pixel Size Y, binned
XBINNING= 1 / Binning factor X
YBINNING= 1 / Binning factor Y
FRAME = 'Light ' / Frame Type
INSTRUME= 'ZWO ASI224MC(C8)-' / Instrument used for acquisition
EGAIN = 0.2636256218 / Electronic gain in e-/ADU
DATE-OBS= '2021-10-01T01:10:53.205' / UTC start date of observation
DATE = '2021-10-01T01:10:53' / Date data written
ORIGIN = 'Mind`s Eye Observatory' / Observatory name
SITELAT = 27.76444444 / Observatory latitude
SITELONG= -80.53416681 / Observatory longitude
OBSERVER= 'John T. Grage' / Observer name
TELESCOP= 'C8 Fastar F1.9' / Telescope used for acquisition
SWCREATE= 'CCDciel Version beta 0.9.75-2382-f758da97 Win32-i386'
OBJECT = 'Preview' / Observed object name
IMAGETYP= 'Light ' / Image Type
GAIN = 250 / Camera gain setting in manufacturer units
XPIXSZ = 3 / [um] Pixel Size X, binned
YPIXSZ = 3 / [um] Pixel Size Y, binned
XBAYROFF= 0 / X offset of Bayer array
YBAYROFF= 0 / Y offset of Bayer array
BAYERPAT= 'RGGB' / Bayer color pattern
FOCALLEN= 386.1 / [mm] Telescope focal length
CCD-TEMP= 33.6 / CCD temperature (Celsius)
FRAMEX = 0 / Frame start x
FRAMEY = 0 / Frame start y
FRAMEHGT= 976 / Frame height
FRAMEWDH= 1304 / Frame width
END
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Re: Start /Mid /End selection for fits file & additional header info

#2

Post by admin »

Hi,

SharpCap 4.0 does have a more complete set of FITS headers (and more appear when you have connected hardware like an ASCOM mount, etc). i.e.

Code: Select all

    SIMPLE  =                    T / C# FITS: 10/01/2021 18:55:17
    BITPIX  =                    8
    NAXIS   =                    2 / Dimensionality
    NAXIS1  =                 1280
    NAXIS2  =                  960
    OBJECT  = 'target name'        /
    GAIN    =                   40 /
    FOCUSPOS=                25000 /
    FILTER  = 'Red     '           /
    EQUINOX =                 2000 /
    OBJCTDEC= '+00 00 00.000'      /
    OBJCTRA = '18 28 51.000'       /
    DEC     = 5.66666666988426E-05 /
    RA      =     277.213894941816 /
    DATE-OBS= '2021-10-01T17:55:17.3886948' / System Clock:Est. Frame Start
    CCD-TEMP=                 23.7 / C
    FRAMETYP= 'Light   '           /
    BLKLEVEL=                    0 /
    YBINNING=                    1 /
    XBINNING=                    1 /
    YPIXSZ  =                 3.75 / microns
    XPIXSZ  =                 3.75 / microns
    EXPTIME =                 0.05 / seconds
    ROWORDER= 'TOP-DOWN'           /
    BSCALE  =                    1 /
    EXTEND  =                    T / Extensions are permitted
    SWCREATE= 'SharpCap v4.0.8208.0, 32 bit' /
    INSTRUME= 'ZWO ASI120MM-S'     /
I think I could pull some of the hardware info from the ASCOM mount to add the lat/long info. The other stuff like observer, telescop etc would require manual entry in the SharpCap settings. I always wonder about the utility of that as most people would never change that (or never even set it up).

I'm also puzzled by the time thing - the DATE-OBS defines the start of the exposure and the EXPTIME field lets you calculate the rest.

cheers,

Robin
Mind's Eye
Posts: 6
Joined: Wed Nov 20, 2019 1:59 pm

Re: Start /Mid /End selection for fits file & additional header info

#3

Post by Mind's Eye »

Thanks Robin,
Actually i just downloaded and installed the most recent version of 4.0. I didn't know that there were new versions out. When I used my older install of Sharpcap and checked for updates there were none. I now know that doesnt tell you there are new versions. So, the next night out I will take a look at the fits headers using 4.0. I haven't been able to do much astronomy due to the Florida summer weather.
I am performing astrometry with my images and the correct way to do measurements as I understand things is the centroid of the object needs to be at a mid frame time. The Minor Planet Center request mid time of exposures and to do it manually for each image set and manually set the time would be time consuming in the workflow.

In my original post I said include a setting but really it's calculating and including that data in the fits file header for use in the astrometry program. I imagine people doing occultations would need the same info.

I understand what you are saying and I am not sure how many people would enter their observatory info for use that way but it would be helpful for anyone using fits to me. When I do live stack astronomy it would not matter. When I do satelite astrometry I take probably tens of thousands frames an observation and they are used with other observers observations so that info in the header would be useful when working with the data. I wouldn't mind manual entry of Lat/Long elv and observer, observatory.

Thanks,
Terry

DATE-OBS Date/time of Start of observation Implemented Start of observation in yyyy-mm-ddThh:mm:ss.s format, unless other interpretation is clearly explained in the comment field. Shutter opening time (?).

DATE-BEG Date/time of start of data New Start of integration.

DATE-AVG Calendar date of mid-point of the observation

DATE-END End of observation New End of observation in yyyy-mm-ddThh:mm:ss.s format, unless other interpretation is clearly explained in the comment field.
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Re: Start /Mid /End selection for fits file & additional header info

#4

Post by admin »

Hi Terry,

I think I can add the timing ones without too much effort (but note - unless you have a QHY GPS camera, all the timings are based on the moment when SharpCap receives the frame from the camera SDK - this is assumed to be the end of the exposure, but it obviously isn't that, since once the exposure ends the USB transfer at the very least has to happen before the frame gets to SharpCap.)

The lat/long are a little more work, but I will see if they can be added. Observer and instrument are the most work, so may not happen just yet.

Update prompts from 3.2 to 4.0 will happen eventually (probably in the next few weeks). I usually give each new major version a relatively long settling in time (time for any bugs to be found and fixed) before prompting people to update from the older version.

cheers,

Robin
Mind's Eye
Posts: 6
Joined: Wed Nov 20, 2019 1:59 pm

Re: Start /Mid /End selection for fits file & additional header info

#5

Post by Mind's Eye »

Hi Robin,
I was thinking about that and I have read a little on the time issue. The software I am using allows the user to select start, mid or end frame from the fits header. Of course I am using start and the software is calculating Mid which is needed for the position solving. This was being done for me and I didnt see that it was. Learning curves are fun! :shock: Interestingly, I have not seen much talk on time calculation in regards to the images themselves and transfer delays. Given the transfer issue which time would be more accurate for a calculation to be taken from? I am using ZWO Asi cameras. Thanks for the information and consideration.

Terry
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Re: Start /Mid /End selection for fits file & additional header info

#6

Post by admin »

Hi Terry,

all the timing points effectively have the same accuracy. SharpCap sets a marker at the moment it receives the frame and flags this as the end time. The start time is calculated by subtracting the exposure length, so if there is any error in the end time, it's in the start time too.

I have just uploaded a new version that adds most of the FITS headers you were asking about - there are even options to manually set the OBSERVER and TELESCOP headers (in the file saving options).

cheers,

Robin
Mind's Eye
Posts: 6
Joined: Wed Nov 20, 2019 1:59 pm

Re: Start /Mid /End selection for fits file & additional header info

#7

Post by Mind's Eye »

Hi Robin,
Very interesting points on the time. A very difficult issue to deal with especially in occultations and timing objects.
That is great and I am going to get the update. Thanks for working on that.

Clear skies,
Terry
procyon12
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Joined: Tue Jan 14, 2020 11:32 am

Re: Start /Mid /End selection for fits file & additional header info

#8

Post by procyon12 »

Hi,

Just made some tests with the latest v4 (4.0.8218.0) under w10 using a (FW-upgraded) QHY174GPS. With the new FITS header infos no issues found. No problems with headers if GPS is enabled.
Thank you, Robin.

Christian
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