Biggest Doug'n'Jim show ever...
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Enjoy!

Emily

Special thanks to Emily, as for obvious reasons she's more than a little busy at the moment!

As you can tell from Jim's last few words, he's enjoying doing these - and I'm having a blast - add them up and we've had 2hrs 41mins of Pancam-o-rama.

Kudos to Jim for working on the Monday that most people take off for a 4 day Indep. W'end

Doug

Does anyone interested to transcript the Doug's interview?

Rodolfo

I have to take exception to one thing that Jim said, about the Pancam field of view. It isn't necessarily as simple as taking the IFOV and multiplying it by the number of pixels, because most optical systems with fields of view more than a few degrees have optical distortions that cause the IFOV to vary slightly from the center to the edge of the field. I'm not sure if the Pancams have appreciable distortion, but the Navcams certainly do.

Great 1/2 hour Doug! It is always a pleasure to ear you and Mr. Bell talking about what you like...

When I sent you the question my interest was mainly on the undergradute students' role, I'm glad Jim Bell followed that path, and even more for seing that he can establish a bridge between the him and Squyres and the new kids in town...
A great future in Mars exploration is guaranteed back there at Cornell.

I can take a little bit later on but I am really busy now getting ready to move in July... more on this later

Thanks Doug, these are really special - I download them and play on iTunes in my car during the commute.

Though judging from Jim's comments about the BBQ pic I fear we may have "defamed" his art! Glad he has a sense of humor about it...

PS - ustrax - did Doug pronounce your name right on the tape? Because I always imagined it differently in my head.....

The origin of 'ustrax' is in a celtic-latin word which means fire...Due to that I say it with a different pronounce, my own, nearer the latin one, it would sound something: 'u' as the 'o' in 'to', the 's' as the 'sh' in 'show', 'trax' was quite near only the 'a' should be a little bit more open as in 'potáto'.
To resume, it should sound like: oshtráx...Or something like that...Sorry if it sounds confusing...
But it was great to ear it!

You didn't hear us chatting about it before I hit the metaphorical record button It was hillarious"

"MY BEAUTIFUL PANORAMA....!!!"



Doug

That must be a British pohtahtoh, rather than an American pertayter.

Well, I hope we cleaned up after the BBQ.... hate to have littered.

Maybe next time you could ask him about the longer term plans for Spirit...surely they must be discussing what they want/can do if she makes it through the winter.

This was a very interesting Q 'n A ! I enjoyed it very much.

Nico

No problem, there is no hurry to read it! The flavor of reading won't miss at any time

Rodolfo

Great as always. Just listened to it on my way to work. It's a pleasure these people take time to explain their work to us. I hope there will be a MER press conference in the near future. It's been a long time since the last one. I am also looking forward to read Jim Bell's blog at the Planetary Society. And yours Doug, too.

Analyst

From JB





Doug

"The reason that the simple "multiply 0.273 by 1024" equation works for Pancam is simply because there is *no* geometric distortion in the optical system." -- Jim Bell, quoted by DE

I'm impressed. As an innocent bystander to the various technical threads on imaging it has all seemed so complicated to me. Can it be? Finally... a simple truth?

Well, Jim certainly knows more about Pancam than I do, but it's a little surprising to me. Maybe it's because the lenses are so optically slow. The radial distortion parameters in the CAHVOR model for Pancam are certainly not zero, but that may be an artifact of the way the CAHVOR pinhole model works.

From Maki et al. [2003]:

"The Hazard Avoidance Cameras (Hazcams) are shown in Figures 8a and 8b. The Hazcams are an f/15 optical system with a focal length of 5.58 mm. The Hazcam optics are f-theta fish-eye lenses with a 124° × 124° horizontal/vertical field of view and a 180° diagonal FOV. The angular resolution at the center of the image is 2.1 mrad/pixel."

[...]

"The Navigation Cameras (Navcams, Figures 4a and 4b) are optically identical to the Descent camera: f/12 cameras with a 14.67 mm focal length. Each Navcam camera has a 45° × 45° field of view (60.7° diagonal), which is roughly equivalent to a 40 mm lens on a 35 mm camera. The angular resolution at the center of the field of view is 0.82 mrad/pixel. The depth of field of the Navcam camera ranges from 0.5 m to infinity, with best focus at 1.0 m."

Doug, thanks for directing me to the more appropriate thread.

I have to disagree with that figure for distortion of 0.01%. There is a fundamental intrinsic distortion present in any optical system, completely independent of the quality of the optics (indeed it exists for a pinhole camera!). It arises because the goal of imaging is always to represent a section of an imaginary sphere surrounding the camera on a flat image plane. In exactly the same way that you cannot represent a section of the earth without distortion on a flat map, any flat image contains fundamentally irreducible distortion (ie even image processing cannot eliminate it).

I suspect the distortion figure that Bell was quoting referred to the amount of pinhole or barrel distortion. These can be eliminated. Thus if we image a grid of straight lines on a card normal to the line of sight, the lines will be straight on the image. But distortions remain, in particular radial and azimuthal angular image scales will have to differ.

Just as with maps of earth, the irreducible distortions increase with the size of the section of the sphere we're imaging, ie with the field of view. It's straightforward to calculate the size of the irreducible distortion.
Suppose we're imaging a circle, normal to the line of sight, whose radius subtends angle theta(radians) at the camera. Then it's angular circumference will be 2 pi sin(theta). Lets suppose the angular image scale is constant in the radial direction. Then, working from the image, if that image scale gives us theta for the radius of the circle, it must give us 2 pi theta for the circumference, in disagreement with the actual circumference of 2 pi sin(theta).

The relative error is specified by the ratio, R = 2 pi sin(theta) / 2 pi theta = sin(theta)/theta. As expected this ratio approaches unity, ie distortion approaches zero, as fov theta approaches zero. For pancam we have theta = 8 degrees, which gives R = 0.9968. Therefore the radial and azimuthal angular image scales must differ by (1 - R) = 0.32%. (Actually the value will be even larger in the corners.) This irreducible distortion is much larger than the quoted value 0.01%.

This ratio R is important when converting pixel separations to angular separations, since the scale factor used to do this (0.273mrad/pixel) must vary by at least 0.32% across the frame and for different orientations. Eg, when comparing a line through the centre of the fov (radial) vs. a line across one edge (more or less azimuthal).

Of course in the end the effect is still small. 0.32% corresponds to an error of only 3 pixels for a 1024 pixel line! Indeed according to the Bell et al JGR (2003) paper, the fov's of the 4 pancams vary by a comparable amount! (It's not clear if this is just measurement uncertainty).