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Voyager camera pointing information
Brian Burns
post Aug 27 2016, 05:45 PM
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QUOTE (mcaplinger @ Aug 27 2016, 11:53 AM) *
If it's a type 1 kernel with no interpolation, then you will only get values at specific times no matter how you set the tolerance -- I think. Does it work for the exact time of an image as calculated using the clock strings instead of the ISO time?

If it is a type 1 you could convert it to type 3 with ckspanit. http://naif.jpl.nasa.gov/naif/utilities_PC...dows_32bit.html


Yes, they're type 1 kernels - they just have pointing information for when the images were taken.

The first photo of Jupiter is C1462321 at 1979-01-05T15:14:10, so I tried this with both kernels but no luck -

CODE
sclkch = "2/14623:21"
sclkdp = spice.scencd(spacecraft, sclkch)
tolerance = spice.sctiks(spacecraft, "0:00:800")

=>

sclkdp 701344783.0
found False


also tried for a later picture, C1504804 at 1979-01-19T19:00:35, and tolerance=1600, but same result.

And tried scanning clock ticks from 0 to a billion, but it didn't find anything -

CODE
tmin = 0
tmax = int(1e9)
tstep = int(1e3)
tolerance = int(1e3)
for t in xrange(tmin,tmax,tstep):
    cmat, clkout, found = spice.ckgp(instrument, t, tolerance, frame)
    if found:
        print cmat


And earlier I had tried scanning through the complete set of Voyager images and used their UTC times to look up pointing information but it didn't find anything.

I've been able to use the position kernels without any problem, so there's something about the pointing kernels that isn't set up correctly.

I know there's information in there somewhere!
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mcaplinger
post Aug 27 2016, 07:39 PM
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QUOTE (Brian Burns @ Aug 27 2016, 09:45 AM) *
I know there's information in there somewhere!

Maybe there's a mismatch between the SCLK-SCET file you're using and the one they used when they generated the C kernels -- this sometimes causes problems. Might be useful to dump the kernel to ASCII with toxfr.

Can't look at this now (busy with other Jupiter images rolleyes.gif ) but maybe next week.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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Brian Burns
post Aug 27 2016, 10:19 PM
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I found the problem - somehow in all the permutations of inputs I missed one - it needed the scan platform instead of one of the cameras - Doh!

I had to dig into the kernel files with some SPICE command line tools to find it - some spacit output -

CODE
--------------------------------------------------------------------------------
   Segment ID     : /usr1/clove/P4/VGR-NEWPTG/V1/a11002.ptg
   Instrument Code: -31000
   Spacecraft     : Body -31, VOYAGER 1
   Reference Frame: Frame 18, ECLIPB1950
   CK Data Type   : Type 3
      Description : Continuous Pointing: Linear Interpolation
   Available Data : Pointing Only
   UTC Start Time : 1977 SEP 05 15:06:11.607
   UTC Stop Time  : 1977 SEP 05 16:48:35.613
   SCLK Start Time: 1/00013:11:001
   SCLK Stop Time : 1/00015:19:001
--------------------------------------------------------------------------------


There it is - Instrument Code: -31000.

And it turned out the NAIF kernel was continuous and the PDS one was discrete - the continuous one works okay but not the discrete one, and I'm not sure why, but I can just use the continuous one. So, finally...

CODE
utc 1979-01-05T15:14:10
et -662330699.816
sclkch 2/14623:20:785
sclkdp 701344767.168
tolerance 799.0
frame ECLIPB1950

cmat [[-0.59495769 -0.46884094 -0.6528503 ]
[-0.50325176 -0.41603515  0.75739846]
[-0.62670808  0.7791681   0.01157828]]
clkout 701344767.168
found True


Now I can do some (approximate) camera pointing!

QUOTE (mcaplinger @ Aug 27 2016, 02:39 PM) *
Can't look at this now (busy with other Jupiter images rolleyes.gif ) but maybe next week.


Can't wait to see what you guys get back!
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mcaplinger
post Aug 27 2016, 10:21 PM
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QUOTE (Brian Burns @ Aug 27 2016, 02:19 PM) *
I found the problem - somehow in all the permutations of inputs I missed one - it needed the scan platform instead of one of the cameras - Doh!

In the new way of doing things you could define a frames kernel with a constant offset between the scan platform frame and the camera frame and it would manage this for you, but the Voyager conversions probably predate that formalism.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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Bjorn Jonsson
post Aug 28 2016, 11:55 PM
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QUOTE (Brian Burns @ Aug 27 2016, 05:45 PM) *
Yes, they're type 1 kernels - they just have pointing information for when the images were taken

Converting a type 1 CK kernel to type 2 is something I have regularly needed to do (I did it for most of the Voyager CK kernels).

This is what I did with the Voyager 2 Neptune CK kernel file (and I used comparable parameters for Jupiter, Saturn and Uranus kernels):

ckspanit -in vg2_nep_version1_type1_iss_sedr.bc -out vg2_nep_test_typ2.bc -typ 2 -tol 9000
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Brian Burns
post Aug 29 2016, 05:22 AM
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Thanks - I guess this means there are gaps in the pointing data... smile.gif

I'm just getting started with this pointing stuff, so it will take me a while to get there. So far I can just project a straight-on view to a simple cylindrical map, but need to incorporate the pointing information and axial tilt, etc. Lots of trigonometry...

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