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Dawn Survey Orbit Phase, First orbital phase
Phil Stooke
post Jul 19 2011, 04:33 PM
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Here's a composite to illustrate that.

Phil

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elakdawalla
post Jul 19 2011, 04:51 PM
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QUOTE (Stefan @ Jul 19 2011, 05:22 AM) *
The last few images were enlarged by an integer factor. Did you find something wrong with how they were enlarged?

The most recent one wasn't -- its enlargement factor was something around 2.2. And the resolutions stated (and widely requoted) in all the released captions are just wrong.

With spherical bodies it is very easy to back out an accurate image resolution from a global image -- measure any diameter and you're done. But for bodies with very different principal axis lengths, especially irregular ones like Vesta, it's hard to do this accurately, which prevents me from doing size comparisons. Size comparison posts are some of the most popular things that I do, which is why this is driving me so crazy.

As of yesterday I think the press person at JPL now understands what I am complaining about, so hopefully we'll see captions fixed soon. Of course what I really want is for them to quit enlarging the released images.


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MarkG
post Jul 19 2011, 04:52 PM
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QUOTE (Phil Stooke @ Jul 19 2011, 08:11 AM) *
Nice one, Mike.

The orange spot in the false color view coincides with the darker spot seen in distant views, including the 'crater with tails' as someone described it, on the edge of the smooth patch we saw a while ago.

Phil


The orange area is around the sub-solar point, so I think it just represents daytime heating. Over time, a strong lead or lag behind nearby features with different times-of-day (Vesta Sols!) would be very interesting.
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Stefan
post Jul 19 2011, 07:14 PM
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QUOTE (elakdawalla @ Jul 19 2011, 06:51 PM) *
The most recent one wasn't -- its enlargement factor was something around 2.2. And the resolutions stated (and widely requoted) in all the released captions are just wrong.


This image was enlarged by a factor 2 (I know because I enlarged it). The resolution of the image as shown here is actually close to the quoted value. But what do you think of the caption here? The media will take that image and do with it whatever they like, and then quote the original numbers.

Yes, I understand your concern about the caption, and no, I didn't write it.
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elakdawalla
post Jul 19 2011, 09:18 PM
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You did the enlargement? It's great to actually talk to someone who knows what's going on smile.gif So tell me where I'm wrong here. The diameter of Vesta in that released image is 860 pixels. At 700 m/pixel (1.4 / 2x enlargement) that gives you 600 km diameter, which I *think* is much too large.

If the pixel scale were rounded incorrectly and the original image scale were 1.3 km/pixel then it would correspond to 560 km diameter, which is within the accepted range of Vestian diameters...

You're right that reporting pixel scales will inevitably result in mainstream media screwing things up. For that reason I'd actually advocate abandoning pixel scales -- ONLY IF the images get released at their original resolution, or if they are enlarged by whole-number factors that are stated in released captions. Those of us who care about these things will get the numbers right.


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Juramike
post Jul 19 2011, 11:39 PM
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Here's a mashup of the image on the DLR website with high-resolution image PIA14313. I took the enhanced-color IR composite and broke it up into little chunks, then took each chunk and warped it to try to align with surface features in the high res image. Reassembled the color composite, then used that to blend to the high-res layer underneath. Full details on flickr (here)

Neat how the scarp and some of the craters and ejecta are greenish in the IR composite.

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Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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dilo
post Jul 20 2011, 07:26 AM
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An update on Dawn trajectory:
in spite of engine running in last 20 hours, the probe is gently accelerating, progressively approaching a "circular orbit speed", as showed below:
Attached Image

The green triangles indicates definitive survey orbit; they are two because I'm not sure if 2700km nominal height is referred to the center or the surface of Vesta... can someone help me? unsure.gif
As additional info, now average acceleration toward Vesta is 3e-5 m/s2 while angle between trajectory and Vesta-to-Dawn vector is approaching 70°.

Addendum: I do not share Emily's bad feeling about image release policy... look to the bright side, last released image was captured only 3 days before and also contrast/gamma is a lot better than previous ones! smile.gif


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Greg Hullender
post Jul 20 2011, 02:13 PM
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Another interesting stat might be energy/kilogram. Although kinetic energy is increasing, potential energy is decreasing.

--Greg
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Stefan
post Jul 20 2011, 03:20 PM
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QUOTE (elakdawalla @ Jul 19 2011, 11:18 PM) *
You did the enlargement? It's great to actually talk to someone who knows what's going on smile.gif So tell me where I'm wrong here. The diameter of Vesta in that released image is 860 pixels. At 700 m/pixel (1.4 / 2x enlargement) that gives you 600 km diameter, which I *think* is much too large.


The distance for that image was (or should have been) 15222 km (center of Vesta). You already know the angular extent of one pixel. You tell me where you are wrong... rolleyes.gif

We are working to improve the caption.

Again, I ask you if you think the enlargement of the last image was done badly. Reading your blog, I am not sure. I used the Mitchell-Netravali algorithm, which I think is appropriate. Remember, it is a tradeoff between blurriness and jagged edge.
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djellison
post Jul 20 2011, 03:29 PM
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QUOTE (Stefan @ Jul 20 2011, 07:20 AM) *
Again, I ask you if you think the enlargement of the last image was done badly.


Why is it being done at all? If (as we have been told) there is a constraint on the teams time in producing images for outreach...why waste some of that precious time in un-necessarily enlarging these images?
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ugordan
post Jul 20 2011, 03:49 PM
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To be fair, that practice of magnifying otherwise poststamp-sized images is pretty much the norm for NASA image advisories, although they do tend to specify the magnification factor in most cases.


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machi
post Jul 20 2011, 06:09 PM
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Enlarging images is standard procedure. NASA use that, almost every amateur processor use that. When one is working with mosaic from multiple images, then resizing is even necessary. When one have post-stamp size image, enlarged variant looks somewhat better, than original one.
"waste some of that precious time"
It's not, in IrfanView (my favorite software for resampling images) it's matter of seconds. smile.gif
"I used the Mitchell-Netravali algorithm, which I think is appropriate."
Mitchell is fine, it's my favorite one, but I think, that it isn't what Emily is complaining about.
She simply need information about actual size of pixels, that's all.


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machi
post Jul 20 2011, 09:41 PM
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South pole of Vesta in stereo. Cross eye and anaglyph version. Resolution is approx. 1 km/pix.
Stereo images were made from one published hi-res image and synthetic image (made from both published hi-res images).
Attached thumbnail(s)
Attached Image
Attached Image
 


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Decepticon
post Jul 20 2011, 09:48 PM
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machi Thank you for the 3D!

My kids appreciate it also!
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Phil Stooke
post Jul 20 2011, 10:11 PM
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Fantastic! Thanks.

Phil


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... because the Solar System ain't gonna map itself.

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