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MARCI Images, ISIS pointers/advice/help much appreciated and desired!
Drkskywxlt
post Aug 18 2010, 07:51 PM
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As part of my research, I'm starting to learn ISIS and display MARCI imagery. I've quickly learned that MARCI imagery is pretty hard to work with since it's a push-frame camera, which a few people claim is the reason there's a relative lack of papers published using its data. I tried to run through the process for an entire pole-to-pole MARCI swath and after processing cam2map for nearly 48hrs, the Linux box booted me off. That's on 8GB of RAM, BTW. After that, I started cropping the images to much smaller chunks. Below is my first recognizably Martian image that I've been able to produce (I've only been at this for a few days). This is from the southern mid-latitude highlands. Some things I don't understand...why is the left part of the frame somewhat washed out/bright? The red/yellow bands around the edge are areas where there apparently is no data in the green or blue channels...not sure why. My processing steps are:

marci2isis
spiceinit
marcical
crop
cam2map
automos

I need to figure out how to really speed this up. I want to look at complete MARCI global mosaics over at least 1 martian year if not the entire MRO mission. At this rate, that would take years laugh.gif . Apparently an ISIS update is coming out in the near future which will help work with LROC WAC images. LROC WAC is also pushframe, so maybe that will help with MARCI imagery as well?

Thanks in advance!
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djellison
post Aug 18 2010, 08:20 PM
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I feel your pain - I tried the exact same process and gave up far earlier than you did.
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Drkskywxlt
post Aug 20 2010, 04:28 PM
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After several more failures, I've got another viewable image. This is on the edge of the southern polar cap. Talked to someone who has done work with LROC WAC (very similar to MARCI). She did it on a 4000-core cluster!! So, basically, you need a supercomputer or darn near to really get the full use of these cameras. I'm looking at using MOC WA images instead...starting to play with those soon.
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stevesliva
post Aug 20 2010, 04:52 PM
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What requires all those cores? You were talking RAM before.

Just curious... memory hogging is far more common than core hogging.
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Drkskywxlt
post Aug 20 2010, 05:08 PM
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QUOTE (stevesliva @ Aug 20 2010, 11:52 AM) *
What requires all those cores? You were talking RAM before.

Just curious... memory hogging is far more common than core hogging.


To make that last image, took about 1.5 hours from start to finish and I used two different 8GB of RAM processors to complete. And that's only a tiny fraction of 1 full MARCI pole-to-pole swath! So, doing 2000 or 4000 of those images at once would let me do several days of MARCI images all at once in the same time.

Apparently, there's no systems where I am that have much more RAM than 8GB. So, you just need lots of cores doing the same thing to speed it up. ISIS is apparently not set up for true parallel-computing yet, although I guess there's been talk to make it so.
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Drkskywxlt
post Aug 20 2010, 05:10 PM
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One more on the other side of the south pole.
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stevesliva
post Aug 20 2010, 06:38 PM
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QUOTE (Drkskywxlt @ Aug 20 2010, 01:08 PM) *
So, doing 2000 or 4000 of those images at once would let me do several days of MARCI images all at once in the same time.

Apparently, there's no systems where I am that have much more RAM than 8GB. So, you just need lots of cores doing the same thing to speed it up. ISIS is apparently not set up for true parallel-computing yet, although I guess there's been talk to make it so.


Oh, batch processing with the batch parallelized. My company's perfectly set up for that sort of thing, which is why I was curious. I can get a few hundred cores on boxes with 256GB of memory, but I'd probably get fired if I did it for images. But like you said, truly SMP or well-threaded applications are more rare. So we just pool lots of machines are throw individual jobs at them.

Interestingly enough, the World Community Grid is set up to do the same sort of thing, albeit with much smaller boxes:
http://www.worldcommunitygrid.org/about_us/viewAboutUs.do

Not sure an RFP for planetary science image processing would fly there... but I would gladly donate you my laptop's 2 cores and 2 GB RAM each night if there were an easy way to set up a client.
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Drkskywxlt
post Aug 20 2010, 07:01 PM
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QUOTE (stevesliva @ Aug 20 2010, 01:38 PM) *
Not sure an RFP for planetary science image processing would fly there... but I would gladly donate you my laptop's 2 cores and 2 GB RAM each night if there were an easy way to set up a client.


Very kind, thanks!
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Drkskywxlt
post Aug 20 2010, 08:25 PM
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The large crater in these two images is Schiaparelli Crater. If you know your Martian geography, you'll know this is just a bit (relatively speaking) east of Opportunity's landing site. The first is what directly comes out of ISIS. It seems the dark albedo features come up as deep blue, not really sure why. I've stretched the colors a bit in the 2nd. Does that look more "Mars-ish"?
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elakdawalla
post Aug 20 2010, 08:42 PM
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It seems the blue channel really brightens to both east and west edges of the mosaic -- is that a photometric effect? MARCI does see a wide longitude strip, and I know photometric effects are what have made it take so long to create the LRO WAC mosaic, but I would have expected it only to brighten on one edge (west), not both. Is it atmospheric scattering?


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Drkskywxlt
post Aug 20 2010, 09:00 PM
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QUOTE (elakdawalla @ Aug 20 2010, 03:42 PM) *
It seems the blue channel really brightens to both east and west edges of the mosaic -- is that a photometric effect? MARCI does see a wide longitude strip, and I know photometric effects are what have made it take so long to create the LRO WAC mosaic, but I would have expected it only to brighten on one edge (west), not both. Is it atmospheric scattering?

Emily...I've been trying to figure that out. Cartrite on the ISIS Support forum notices the same effect, but it never really gets answered by the ISIS staff. I cropped the sides off the image off, and that helps. When I keep the full image width, there's just bright blurs on each side. I suspect it might be an atmospheric effect, but I don't know enough about imagery and the cameras to make an educated guess.
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volcanopele
post Aug 20 2010, 09:15 PM
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Could it be due to scattered light in the optics of the camera system? Have to deal with that a lot with the WAC on Cassini.


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djellison
post Aug 20 2010, 11:13 PM
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Rememebr the FOV of MARCI is HUGE. The edges you're looking really out left and right from the spacecraft so whilst it's nicely map projects, you're looking through a lot more atmosphere, and I don't think that's something you can easily calibrate out and is probably what's causing the problem.
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ugordan
post Aug 20 2010, 11:45 PM
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Yup, probably a combination of Rayleigh scattering and just plain dusty atmosphere at highly off-nadir look angles.


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mwolff
post Aug 21 2010, 01:33 AM
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QUOTE (elakdawalla @ Aug 20 2010, 02:42 PM) *
It seems the blue channel really brightens to both east and west edges of the mosaic -- is that a photometric effect? MARCI does see a wide longitude strip, and I know photometric effects are what have made it take so long to create the LRO WAC mosaic, but I would have expected it only to brighten on one edge (west), not both. Is it atmospheric scattering?



Finally, a question that I can answer with some knowledge! The brightening on the west side is due primarily to atmospheric effects, but it is a combination of simple atmospheric pathlength (i.e., larger emergence angles) and decreasing scattering angle (i.e., climbing the the phase function towards the forward scattering peak). On the east side, it can also involve surface photometry as the low phase angle range (where opposition effects are more prevalent) can range quite a portion of the image in terms of north south. In addition, on the east side, you have the double air mass (large incidence and emergence angles) effect to counteract the decreased amplitude of the scattering phase function at lower phase angles.

The presence of even a small amount of water ice haze can dramatically increase these effects...dust tends to be more neutral on the eastern side of the strips.
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