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Juno PDS data
Bjorn Jonsson
post Jun 8 2018, 12:16 PM
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QUOTE (Gerald @ Jun 7 2018, 11:42 PM) *
Any of my attempts to define a globally accurate lense distortion model on the basis of Brown-Conrady with only 4 free parameters failed thus far. Locally it's no problem to go below 1/100 pixel accuracy with respect to some error metrics. But I would have been surprised, if Brown-Conrady would have worked so easily for global lense geometry. With an increasing number of non-zero parameters, the Brown-Conrady model becomes more and more unstable and unrealistic. That issue is well-known since several decades, at least, (probably more than a century in some cases) for other approximations derived from Taylor polynomials. (Think, e.g. of splines of polynomials of degree 7 rather than cubic splines. They oscillate too much to be useful in practice.) Therefore, I'll consider approaches rather different from Brown-Conrady. But I can't tell which of the long list of those more or less straightforward alternatives will be as successful as required, before it's elaborated and tested. Those methods have their own specific issues.


I can imagine it might be difficult to find a mathematical function that works well everywhere if you want this level of accuracy - there could be various minor 'irregularities'. For example minor distortions might not be perfectly symmetrical around the optical axis at this level of accuracy.

I wonder if it might make sense to measure control points using stars in JunoCam images and then triangulate the control points. Another set of triangulated control points would contain the known, correct (i.e. without optical distortions) positions of the stars. You could then determine an affine transform for each triangle and use this to map from distorted pixel positions to non-distorted positions or vice versa. A possible drawback is that you might need a lot of control points (i.e. small triangles) for sufficient accuracy.
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fredk
post Jun 8 2018, 02:38 PM
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Sorry for not having followed all the details in this thread, but what do you use to fit the B-C parameters? Are you finding the best-fit parameters from images of Jupiter using its modeled shape/position? Or are you using images that show stars? It seems the latter would avoid any modeling uncertainties in the shape of Jupiter since the stars' true directions are precisely known.
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mcaplinger
post Jun 8 2018, 03:07 PM
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QUOTE (fredk @ Jun 8 2018, 06:38 AM) *
Sorry for not having followed all the details in this thread, but what do you use to fit the B-C parameters?

The Junocam I kernel parameters were fit using stars from the cruise imaging and validated using the positions of the galilean satellites during PJ1.

How Gerald's processing works with regard to camera parameters has never been clear to me.

I am personally of the opinion that expecting deep sub-pixel registration between bands is a pipe dream, but obviously I could be wrong.


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Brian Swift
post Jul 26 2018, 04:19 AM
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Anyone have a script/tool to bulk download raw data and metadata from missionjuno site that they are willing to share?
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Brian Swift
post Aug 1 2018, 06:42 PM
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Mike, two unrelated questions:

1. How many different image compression quality level settings are used by junocam on a typical peri-jove?

2. "FOCAL_PLANE_TEMPERATURE" appears to always be "273.0 <K>". Is this a bug or a feature (of very precise temp control)?
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mcaplinger
post Aug 1 2018, 09:37 PM
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QUOTE (Brian Swift @ Aug 1 2018, 10:42 AM) *
1. How many different image compression quality level settings are used by junocam on a typical peri-jove?

2. "FOCAL_PLANE_TEMPERATURE" appears to always be "273.0 <K>". Is this a bug or a feature (of very precise temp control)?

1) It depends, but nearly all of the lossy images have been taken with the same compression requantization parameter for the past several PJs, with an occasional single image with a little higher value.

2) For a variety of reasons, the 273K value basically means that the software couldn't easily figure out the FPA temperature. None of our processing so far tries to do anything with the FPA temperature, so we haven't tried to fix this problem very aggressively.

Sending a message to jncdata@msss.com is the prescribed way of asking questions about the PDS products.


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Gerald
post Sep 23 2018, 12:39 PM
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QUOTE (fredk @ Jun 8 2018, 04:38 PM) *
Sorry for not having followed all the details in this thread, but what do you use to fit the B-C parameters? Are you finding the best-fit parameters from images of Jupiter using its modeled shape/position? Or are you using images that show stars? It seems the latter would avoid any modeling uncertainties in the shape of Jupiter since the stars' true directions are precisely known.

I've given a partial answer to these questions at EPCS a few days ago.
Here are the slides of the talk.

I'll refine this further over the next several weeks in background processes, and may occasionally provide according SPICE kernels.
There are some more methods for calibration and cross-checking, only partially implemented as of yet.
I've also written up portions of the deeper theoretical background. But that's not yet available online.

I've used stars for calibration purposes a few years ago. But they have their own issues, e.g. real or optical binaries with unclear centroid, TDI blur, background noise, few photons, aliasing, velocity aberration (can be adjusted for in a formal way), etc.
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fredk
post Sep 24 2018, 03:20 PM
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Thanks for the details, Gerald. Can you point to some starfield images?
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Gerald
post Sep 24 2018, 07:09 PM
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You'll find some material, if you go back to post #8 in this thread.

But you can also take a more extended look at the JunoCam cruise images in the PDS.
The EDRs are starting here. Check for possible DCT decoding issues.
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Brian Swift
post Sep 26 2018, 06:32 AM
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QUOTE (fredk @ Sep 24 2018, 08:20 AM) *
Thanks for the details, Gerald. Can you point to some starfield images?

The starfield image filenames and point source (stars/moons) correspondences used in my camera modeling process are available in file Juno24Matchpoints.csv on my JunoCam Github page.

These are full revolution images that appear to have relatively low amounts of compression.

This post from April has an overview of my process.
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Brian Swift
post Sep 28 2018, 04:11 PM
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Question for everyone, what tool(s) do you use to identify objects (moons/stars) in an instrument's field of view?
I'm currently looking at the SPICE enhanced Cosmographia from NAIF, and Celestia.
If I used SPICE routines directly, it appears I'd have to iterate through all the known objects testing each one to see if it in the FOV.
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Gerald
post Sep 28 2018, 05:13 PM
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Depends on the purpose. For JunoCam calibration, I've used the Bright Star Catalog (BSC), together with a home-made rendering tool. But sometimes, the printed Uranometria 2000.0, or the offline tool Red Shift. Sometimes, the online astrometry.net can help, or Google Sky. Or Eyes on Juno. There are several more star catalogs, etc.
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mcaplinger
post Sep 28 2018, 06:10 PM
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QUOTE (Brian Swift @ Sep 28 2018, 08:11 AM) *
Question for everyone, what tool(s) do you use to identify objects (moons/stars) in an instrument's field of view?...
If I used SPICE routines directly, it appears I'd have to iterate through all the known objects testing each one to see if it in the FOV.

Yep. I just use a small subset of the BSC and loop as follows (note, no aberration correction):

CODE
readstars("bscbrite")
for i in range(0,nframes):
t = t0+i*interf
c = pxform("j2000", "juno_junocam", t)
for s in stars:
if stars[s][2]>3.5: continue # skip stars that are too dim
to_star = radec(stars[s][0], stars[s][1])
to_star = mxv(c, to_star)
fl = 10.997/7.4e-3
alpha = to_star[2]/fl
cam = [to_star[0]/alpha, to_star[1]/alpha]
cam = distort(cam)
cam[1] += yoff
if to_star[2] > 0 and abs(cam[0])<1648/2 and abs(cam[1])<128/2:
x = cam[0]+1648/2
y = cam[1]+128/2
print s, stars[s][2], x, y+i*128


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Brian Swift
post Oct 9 2018, 05:49 PM
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Thanks Mike, Gerald. I ended up using Cosmographia to determine the names of the stars from a few frames, used simbad to look up their Hipparcos id, which I used to lookup ra-dec in a Hipparcos catalog I downloaded form NAIF. After working out the SPICE frame transforms using the few stars, I was able to automatically match all my detected "stars". Then investigated a couple outlier matches, which turned out to Ganymede and Saturn.
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Brian Swift
post Oct 9 2018, 05:55 PM
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Mike, just curious, is there an explanation for the 20 msec START_TIME jitter that is mentioned in juno_junocam_v02.ti?
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