Starship Asterisk*

by **Nitpicker** » Tue Jan 06, 2015 6:54 am

Chris Peterson wrote: This might be of interest.

M-933-72-17-T6.jpg
If I'm reading this correctly, the initial descent orbit insertion (DOI-1) was performed by the CSM while it was still docked with the LM. This placed the pair in a highly eccentric orbit (59 / 14.5 nmi). Then we have separation, followed by a short CSM burn that placed it in a slightly different orbit (61.5 / 11.5 nmi). In this orbit, it was lower than the LM at times. Then, the CSM performed another burn to circularize its orbit (required for redocking). Here, too, the CSM perilune (54 nmi) is below the LM apolune (59 nmi). Finally, the LM performs DOI-2, increasing its apolune and decreasing its perilune (59.6 / 6.2 nmi). Still, we have orbit segments where it is higher than the CSM.

These various orbits were maintained for more than two hours after undocking, so there were ample opportunities to photograph the CSM between the Moon and the LM. I think these images were taken shortly before the PDI burn that braked the LM out of lunar orbit and began the final descent.

I've been looking at this a little more closely ... these low lunar orbits have a period of about two hours, so the source images for the APOD, one orbit before landing, are most likely to have been taken about half an hour after the "CSM SEP" burn and about an hour before the "CSM CIRC" burn. This makes more sense, as I calculate the LM to be only about 18 vertical kilometres above the landing site, which in turn is just less than 5 km higher than the arbitrary zero vertical datum of 1,730 km from the centre of the Moon (which I suspect was used for the Apollo missions). This would put the LM's altitude, relative to the zero datum, at about 23 km, or 12 to 13 nautical miles, which is not too far off the quoted "RESULTING PERILUNE" of the "DOI-1" burn, which occurred about nine orbits earlier. (I would expect the LM to be near its perilune, one orbit before landing.) Also, the quoted "VELOCITY CHANGE" of 1.0 ft/s generated by the little "CSM SEP" burn, would have separated the two craft by 700 metres (my earlier estimation) after 38 minutes and given the CSM a slightly lower perilune, so that is a close match as well.

Note that my estimations were not made with terribly high precision and are predicated on the lens focal length being equal to the nominal 60 mm, which may not be exact in this image. But I'm confident I'm in the right ball park.

by **Nitpicker** » Tue Jan 06, 2015 1:19 am

Chris Peterson wrote:
Nitpicker wrote:I will agree with you that an anaglyph made with normal eye separation is a special case and does not distort our depth perception compared with the natural scene. Yet all anaglyphs, holograms, etc, may be defined as illusions for other reasons, as 2-D planes in space are perceived by our brains to have depth dimensions, making them 3-D images. This differs from the 3-D image of a statue, for instance, which exists in 3-D space.
By that logic a photograph is an illusion, as well. You may choose to consider it as such, but I would not.

No, I suppose that's where I draw the line (to conjure a mental image). A "2-D image" plane does not give the binocular illusion of depth like a "3-D image" plane. Any illusion of depth provided by a "2-D image" plane is based only on the monocular depth perception available to an immovable, one-eyed person, with the possible addition of a narrower focal depth. A two-eyed person has no advantage in looking at a "2-D image" plane.

by **Chris Peterson** » Tue Jan 06, 2015 12:49 am

Nitpicker wrote:I will agree with you that an anaglyph made with normal eye separation is a special case and does not distort our depth perception compared with the natural scene. Yet all anaglyphs, holograms, etc, may be defined as illusions for other reasons, as 2-D planes in space are perceived by our brains to have depth dimensions, making them 3-D images. This differs from the 3-D image of a statue, for instance, which exists in 3-D space.

By that logic a photograph is an illusion, as well. You may choose to consider it as such, but I would not.

by **Nitpicker** » Tue Jan 06, 2015 12:43 am

Chris Peterson wrote:
Nitpicker wrote:And based on the most simple definition of an illusion as "a distortion of the senses", I'd call anaglyphs illusions. That the exaggerated depth perception observable in the anaglyph makes this scene look like a small model, is the illusion.
A stereo pair need not distort the senses at all. So while an anaglyph made with a wide separation produces the diorama effect, and could be called an illusion, it could also be made with normal eye separation (as with a conventional stereo camera) and would produce a completely realistic, true 3D image. That certainly would not be an illusion.

I will agree with you that an anaglyph made with normal eye separation is a special case and does not distort our depth perception compared with the natural scene. Yet all anaglyphs, holograms, etc, may be defined as illusions for other reasons, as 2-D planes in space are perceived by our brains to have depth dimensions, making them 3-D images. This differs from the 3-D image of a statue, for instance, which exists in 3-D space.

by **Chris Peterson** » Tue Jan 06, 2015 12:21 am

Nitpicker wrote:And based on the most simple definition of an illusion as "a distortion of the senses", I'd call anaglyphs illusions. That the exaggerated depth perception observable in the anaglyph makes this scene look like a small model, is the illusion.

A stereo pair need not distort the senses at all. So while an anaglyph made with a wide separation produces the diorama effect, and could be called an illusion, it could also be made with normal eye separation (as with a conventional stereo camera) and would produce a completely realistic, true 3D image. That certainly would not be an illusion.

by **Nitpicker** » Mon Jan 05, 2015 11:50 pm

Chris Peterson wrote:
Nitpicker wrote:If we had been in the LM observing this scene, we would have been able to wink alternately, or shift our head a little from side to side, in order to determine that the CSM was much closer than the Moon.
In fact, we would not, because there would not be enough parallax to engage our 3D vision.

But with this anaglyph, the original images were taken a very long way apart compared with human eye spacing. So, our brains perceive a sense of depth that is artificially exaggerated because our brains are unable to interpret it in any other intelligible way. Hence why I'd call it an illusion.
I wouldn't call it an illusion. We've simply changed the scale of the 3D parallax by increasing the separation between the two images.

I'll concede that winking alternately, on its own, would not be sufficient in this case. We'd also need to rely on the relative motion of the CSM against the lunar background. Increase the parallax by five times though (by moving ones head side to side by about half a metre, say) and the change in angles increases to an amount detectable, based on the 20/20 human visual acuity of one arcmin.

And based on the most simple definition of an illusion as "a distortion of the senses", I'd call anaglyphs illusions. That the exaggerated depth perception observable in the anaglyph makes this scene look like a small model, is the illusion.

by **Chris Peterson** » Mon Jan 05, 2015 10:01 pm

Nitpicker wrote:If we had been in the LM observing this scene, we would have been able to wink alternately, or shift our head a little from side to side, in order to determine that the CSM was much closer than the Moon.

In fact, we would not, because there would not be enough parallax to engage our 3D vision.

But with this anaglyph, the original images were taken a very long way apart compared with human eye spacing. So, our brains perceive a sense of depth that is artificially exaggerated because our brains are unable to interpret it in any other intelligible way. Hence why I'd call it an illusion.

I wouldn't call it an illusion. We've simply changed the scale of the 3D parallax by increasing the separation between the two images.

by **Nitpicker** » Mon Jan 05, 2015 9:20 pm

Chris Peterson wrote:
Most stereo pair images of astronomical objects create a diorama effect. In this scene, our eyes are far too close together to be able to see any depth on the Moon, or to see that the CSM is between us and the Moon. The two images were made not a few centimeters apart like our eyes, but many meters apart. That creates much more parallax and lets us see true depth... but our brain can only interpret it assuming the short baseline between our eyes, so we tend to interpret the image as if we were looking down on a small model of the Moon, rather than the real thing.

If we had been in the LM observing this scene, we would have been able to wink alternately, or shift our head a little from side to side, in order to determine that the CSM was much closer than the Moon. But with this anaglyph, the original images were taken a very long way apart compared with human eye spacing. So, our brains perceive a sense of depth that is artificially exaggerated because our brains are unable to interpret it in any other intelligible way. Hence why I'd call it an illusion. The placement of the CSMs in the anaglyph could be altered a little to make it seem closer or further away. I am not sure if that particular trick can be done accurately in a universal way, for all viewers, to represent the actual distance ratios. And I am not sure it has been done accurately in this case, compared with the actual distances measured. But it still looks very, very cool.

by **Chris Peterson** » Mon Jan 05, 2015 3:08 pm

Nitpicker wrote:My calculations based on image 22467 and a scale map of the landing site, locate the CSM at ~0.7 km from the camera, and the peak of the South Massif (immediately behind the CSM) at ~43 km from the camera. So, the peak is about 60 times further away from the camera than the CSM. But that's as far as I'm able to take things. I'm not familiar enough with the way anaglyphs work, to know how much the CSM from image 22466 should have been shifted, to make the CSM appear to be 60 times closer than the peak in the anaglyph. I'm not even sure that's possible to calculate in a universal way for all viewers, given that anaglyphs only create an illusion of 3-D.

I wouldn't say that the effect is just an illusion. Stereo pairs create true 3D as perceived by us, or any creature with a pair of eyes. They only differ from reality in the sense that we are presented a single view, and can't change our orientation (although virtual reality displays get around this by presenting different stereo pairs with changing attitude and orientation).

An anaglyph simply presents the stereo pair superimposed, using color filters to separate the left and right eye. Whatever mechanism is used, though, the math is trivial- it's just a simple parallax calculation. So if you know the relative distance between two objects, you also know the relative shift.

Most stereo pair images of astronomical objects create a diorama effect. In this scene, our eyes are far too close together to be able to see any depth on the Moon, or to see that the CSM is between us and the Moon. The two images were made not a few centimeters apart like our eyes, but many meters apart. That creates much more parallax and lets us see true depth... but our brain can only interpret it assuming the short baseline between our eyes, so we tend to interpret the image as if we were looking down on a small model of the Moon, rather than the real thing.

by **Nitpicker** » Mon Jan 05, 2015 11:46 am

My calculations based on image 22467 and a scale map of the landing site, locate the CSM at ~0.7 km from the camera, and the peak of the South Massif (immediately behind the CSM) at ~43 km from the camera. So, the peak is about 60 times further away from the camera than the CSM. But that's as far as I'm able to take things. I'm not familiar enough with the way anaglyphs work, to know how much the CSM from image 22466 should have been shifted, to make the CSM appear to be 60 times closer than the peak in the anaglyph. I'm not even sure that's possible to calculate in a universal way for all viewers, given that anaglyphs only create an illusion of 3-D.

by **Nitpicker** » Mon Jan 05, 2015 4:43 am

Chris Peterson wrote:
Nitpicker wrote:Thinking a bit more about this, it seems plausible to me that the shifted position of the CSM from 22466 is intended to represent the position of the CSM from 22467, as it might have appeared from the LM if only the LM was moving relative to the Moon.
With the available information, that would be extremely difficult to work out analytically. I think it was just shifted a bit to yield a good visual result.

In the engineering world -- especially engineering drawing -- that's often the same thing.

by **Chris Peterson** » Mon Jan 05, 2015 4:09 am

Nitpicker wrote:Thinking a bit more about this, it seems plausible to me that the shifted position of the CSM from 22466 is intended to represent the position of the CSM from 22467, as it might have appeared from the LM if only the LM was moving relative to the Moon.

With the available information, that would be extremely difficult to work out analytically. I think it was just shifted a bit to yield a good visual result.

by **Nitpicker** » Mon Jan 05, 2015 3:40 am

Thinking a bit more about this, it seems plausible to me that the shifted position of the CSM from 22466 is intended to represent the position of the CSM from 22467, as it might have appeared from the LM if only the LM was moving relative to the Moon.

by **Nitpicker** » Sun Jan 04, 2015 11:05 pm

The CSM from 22467 has also been shifted more into the shadow of the South Massif, which at least reveals slightly more detail on the South Massif. And of course, the images have been rotated ~90 degrees clockwise, which I assume spares us from viewing the anaglyph with our heads tilted to the left.

(And certainly, based on the appearance of the central fiducial cross-hairs in the anaglyph, it is composed from original images 22466 and 22467.)

Edit: actually, I'm probably wrong about the shifting of the CSM from 22467. It looks instead like the CSM from 22466 has simply been shifted to a position later than the position shown in 22467. (I haven't pulled out my red-blue glasses yet, nor have I separated the channels as Chris has done. Although I recall viewing this anaglyph in 3-D a few months ago: http://asterisk.apod.com/viewtopic.php? ... 51#p222151.)

by **Chris Peterson** » Sun Jan 04, 2015 4:11 pm

DavidLeodis wrote:Thanks Chris :).

Hoping not to sound like I seek out possible errors in APOD explanations (which I do not not) I've now noticed that whereas the explanation states "The stereo anaglyph was assembled from two photographs (AS17-147-22465, AS17-147-22466)" in the information with the anaglyph brought up through the "The scene was recorded" link it states the images used "are AS17-147-22466 and 67". I'm :? but not for the first time :wink:.

Interesting. There is some major image fudging going on here. The two images used are 22467 for the cyan channel, and 22466 for the red channel. But 22466 has been altered from the original: the position of the CSM has been changed. It has been erased and cloned into a new position. I'm sure that's because it has moved too far between the two frames for the eyes to accomplish a 3D merge. But it also means that it's anybody's guess just how the actual 3D visual appearance of this scene actually was.

Left is the original, right is the modified.

by **DavidLeodis** » Sun Jan 04, 2015 3:15 pm

Thanks Chris

.

Hoping not to sound like I seek out possible errors in APOD explanations (which I do not not) I've now noticed that whereas the explanation states "The stereo anaglyph was assembled from two photographs (AS17-147-22465, AS17-147-22466)" in the information with the anaglyph brought up through the "The scene was recorded" link it states the images used "are AS17-147-22466 and 67". I'm

but not for the first time

.

by **Chris Peterson** » Sun Jan 04, 2015 2:50 pm

DavidLeodis wrote:Patrick Vantuyne is a link that brought up some information (dated July 2008) about Patrick and had a link to his website. When I click on that that link I however get a message "Forbidden. You don't have permission to access / on this server. Additionally, a 404 Not Found error was encountered while trying to use an Error Document to handle the request.". I wonder if this is a problem with my connection or are others getting the same problem, or is it that the link may be old and is now dead but if so why does the "Forbidden. You don't have permission to access / on this server" come up as that would seem to imply the link is still live. :?

The domain is still active. But the site is not... it looks like a badly configured Apache server.

by **DavidLeodis** » Sun Jan 04, 2015 1:04 pm

Patrick Vantuyne is a link that brought up some information (dated July 2008) about Patrick and had a link to his website. When I click on that that link I however get a message "Forbidden. You don't have permission to access / on this server. Additionally, a 404 Not Found error was encountered while trying to use an Error Document to handle the request.". I wonder if this is a problem with my connection or are others getting the same problem, or is it that the link may be old and is now dead but if so why does the "Forbidden. You don't have permission to access / on this server" come up as that would seem to imply the link is still live.

by **Nitpicker** » Sat Jan 03, 2015 9:55 pm

Very satisfying answers. Thanks all.

by **Chris Peterson** » Sat Jan 03, 2015 8:46 pm

geckzilla wrote:
Chris Peterson wrote:
geckzilla wrote:Oh, right, so they are orbiting together and bobbing up and down in their eccentric orbits and this doesn't have to be right after separation. Almost seems like the possibility of collision exists. For the CSM to be that large in the photo there is no way it is very distant. Only a few hundred meters. I guess < 500m
Hard to say. It might be farther than you think. In principle, we might figure out from the features and horizon curvature what the image scale is. The CSM is 11 meters long; it could easily be several kilometers away given a normal range telephoto.
It is apparently easy to find out the properties of the camera which took the images.
http://www.lpi.usra.edu/resources/apoll ... -147-22467
60mm focal length?

The fiducials are 10 mm apart. So the plate scale on the original scan is 1.26 arcmin/pixel. Assuming the CSM is tipped away at about 60° (the circular end appears about twice as wide as high), that suggests a distance of 515 meters. Doing the same calculation using the diameter of the CSM (rotation angle independent, but only a few pixels) gives a distance of 710 meters.

I think it's reasonable to say the separation was between 500 and 1000 meters in these images.

by **geckzilla** » Sat Jan 03, 2015 8:07 pm

Chris Peterson wrote:
geckzilla wrote:Oh, right, so they are orbiting together and bobbing up and down in their eccentric orbits and this doesn't have to be right after separation. Almost seems like the possibility of collision exists. For the CSM to be that large in the photo there is no way it is very distant. Only a few hundred meters. I guess < 500m
Hard to say. It might be farther than you think. In principle, we might figure out from the features and horizon curvature what the image scale is. The CSM is 11 meters long; it could easily be several kilometers away given a normal range telephoto.

It is apparently easy to find out the properties of the camera which took the images.
http://www.lpi.usra.edu/resources/apoll ... -147-22467
60mm focal length?

by **Chris Peterson** » Sat Jan 03, 2015 8:01 pm

puke wrote:So this is the best you can come up with?
A 42 year old B/R 3D picture of the moon?
I mean with all the new items being seen everyday , this is all you can come up with?

Yeah, I know what you mean. I was recently at The Louvre, and all they had was a bunch of old stuff. Seriously, you have to wonder, with all the new stuff that's out there, why they're wasting space with the Mona Lisa and so much other irrelevant garbage.

by **Beyond** » Sat Jan 03, 2015 7:58 pm

puke wrote:So this is the best you can come up with?
A 42 year old B/R 3D picture of the moon?
I mean with all the new items being seen everyday , this is all you can come up with?
It isn't even the anniversary of when it was taken.

Hello, aptly named person. The moon landing was a current event for me when it happened. It's nice once in a while to catch some of the goings on that weren't broadcast. IF you don't care much for such events, just ask for your money back, or wait for an APOD you do like. In the meantime, it would be nice if you helped maintain the quiet, cordial atmosphere of the Good ship Asterisk*
Thank you.

Beyond

by **puke** » Sat Jan 03, 2015 6:58 pm

So this is the best you can come up with?
A 42 year old B/R 3D picture of the moon?
I mean with all the new items being seen everyday , this is all you can come up with?
It isn't even the anniversary of when it was taken.

by **Chris Peterson** » Sat Jan 03, 2015 5:09 pm

geckzilla wrote:Oh, right, so they are orbiting together and bobbing up and down in their eccentric orbits and this doesn't have to be right after separation. Almost seems like the possibility of collision exists. For the CSM to be that large in the photo there is no way it is very distant. Only a few hundred meters. I guess < 500m

Hard to say. It might be farther than you think. In principle, we might figure out from the features and horizon curvature what the image scale is. The CSM is 11 meters long; it could easily be several kilometers away given a normal range telephoto.

I imagine that the burns that produced separate orbits also resulted in slightly different inclinations as well as different apo- and perilunes. All in all, the possibility of a collision seems extremely small, even assuming that the orbits weren't deliberately designed to avoid one (which I don't know was done, but given how carefully the mission was designed, I'd be surprised if that possibility wasn't factored in).

Starship Asterisk*

APOD: Apollo 17: A Stereo View from Lunar... (2015 Jan 03)

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