IPD and LSD, what is different?

I admit, I had a different definition of LSD in mind. :lol:

I don't think that Lens Separation Distance is a recognized technical term. Perhaps someone was comparing their IPD in relation to the separation of the Rift's lenses?

The lens separation distance is the distance between the centers of the two lenses in the Rift. For the current Rift, this is fixed since the lenses never move. The interpupillary distance (IPD) is the distance between the pupils of the user's eyes. This varies per person; for example, a male user is likely to have a larger IPD than a female user.

As far as your software is concerned, the lens separation distance should just be a fixed value (at least, for this version of the Rift: 64mm) and should be used to determine how to center the rendered image directly behind the lens center. You always center the rendering behind the lens centers, regardless of the user's IPD. The IPD should be configurable to match your user, and used to separate the position of the virtual cameras.

As an example, let's say your user has an IPD of 66mm. This mean you should separate the two virtual cameras in your world by the equivalent of 66mm (see equation 10 of the SDK overview). Just apply a translation of -33mm to the left eye and +33mm to the right eye (converting to world units). Then you perform the projections for each camera and apply another translation to account for the offset of the lenses from each half of the screen - this is calculated from the lens separation distance (see equations 6 to 9 and 14). The offset is positive for the left eye and negative for the right eye, since the lenses are closer to the middle of the Rift than the sides.

"sftrabbit" wrote:
The lens separation distance (LSD) is the distance between the centers of the two lenses in the Rift.

LSD is not a common acronym for "Lens Separation Distance" (more commonly know as "Lens Interaxial Distance", or for stereoscopic photography "stereo base" or "stereobase"). It is also incorrectly called "Interoccular Distance" in many online documents, but really refers only to eyes and not real or virtual cameras. Although you will also find documents that call it "Lens Separation Distance", LSD is not a commonly recognized acronym for anything other that the widely know and recognized hallucinogenic drug (and using it for anything else only causes momentary interpretation conflict while reading).

http://www.stereoeye.jp/software/sbcalc_e.html
http://www.dashwood3d.com/blog/beginners-guide-to-shooting-stereoscopic-3d/
http://www.waset.org/journals/waset/v59/v59-408.pdf

Let's not be intentionally confusing by using obfuscated acryonym hijacking like this thread proposes. Instead of the confusing LSD acronym, we should call this by its generally recognized terminology of "Interaxial Distance" or "Stereo Base".

And besides, do you really want to waste tax dollars because the government computers flagged your post for human review from the suspicious "LSD" keyword contained in it?

"geekmaster" wrote:

"sftrabbit" wrote:
The lens separation distance (LSD) is the distance between the centers of the two lenses in the Rift.

LSD is not a common acronym for "Lens Separation Distance" (more commonly know as "Lens Interaxial Distance", or for stereoscopic photography "stereo base" or "stereobase"). It is also incorrectly called "Interoccular Distance" in many online documents, but really refers only to eyes and not real or virtual cameras. Although you will also find documents that call it "Lens Separation Distance", LSD is not a commonly recognized acronym for anything other that the widely know and recognized hallucinogenic drug (and using it for anything else only causes momentary interpretation conflict while reading).

http://www.stereoeye.jp/software/sbcalc_e.html
http://www.dashwood3d.com/blog/beginners-guide-to-shooting-stereoscopic-3d/
http://www.waset.org/journals/waset/v59/v59-408.pdf

Let's not be intentionally confusing by using obfuscated acryonym hijacking like this thread proposes. Instead of the confusing LSD acronym, we should call this by its generally recognized terminology of "Interaxial Distance" or "Stereo Base".

And besides, do you really want to waste tax dollars because the government computers flagged your post for human review from the suspicious "LSD" keyword contained in it?

I was only referring to it as LSD for brevity because bispro89 had already done so - not because it's a common way to do it. Nonetheless, it is called the LensSeperationDistance in the Oculus SDK Overview, which is what I was making reference to.

"sftrabbit" wrote:
... I was only referring to it as LSD for brevity because bispro89 had already done so - not because it's a common way to do it. Nonetheless, it is called the LensSeperationDistance in the Oculus SDK Overview, which is what I was making reference to.

It is very self-explanatory when spelled out, perhaps even more clear than "more common" industry terminology, but confusing as a non-standard "LSD" acronym.

Oh my. I never expected that chaos with my wrong terminology, 'LSD'. Do not misunderstand me. I am far from any drungs, even cigarette. I'd rather call it 'Interaxial Distance' then..

even though sftrabbit explained me a lot, I still confused with these two, IPD and Interaxial Distance things..

It is precise of what i am confused with these two. Let me narrow down this discussion.
When i use rift device, Interaxial Distance(lens separation distance) is fixed to 64mm, as document say so.
But even so, how can IPD have different value with Interaxial Distance? Even though users' IPD differs, they look through same lens, with same physical distance between lens centers. If so, IPD just don't have any meaning, since Interaxial Distance is all that counts, not IPD. Am i missing something?

can anybody make it clear please?

"bispro89" wrote:
If so, IPD just don't have any meaning, since Interaxial Distance is all that counts, not IPD. Am i missing something?

can anybody make it clear please?

IPD definition:

"

"bispro89" wrote:
Oh my. I never expected that chaos with my wrong terminology, 'LSD'. Do not misunderstand me. I am far from any drungs, even cigarette. I'd rather call it 'Interaxial Distance' then..

even though sftrabbit explained me a lot, I still confused with these two, IPD and Interaxial Distance things..

It is precise of what i am confused with these two. Let me narrow down this discussion.
When i use rift device, Interaxial Distance(lens separation distance) is fixed to 64mm, as document say so.
But even so, how can IPD have different value with Interaxial Distance? Even though users' IPD differs, they look through same lens, with same physical distance between lens centers. If so, IPD just don't have any meaning, since Interaxial Distance is all that counts, not IPD. Am i missing something?

can anybody make it clear please?

Yes, everything you said is right - if you're only concerned about the Rift side of things. But you also need to think about how you'll be rendering your game. You need to best recreate what the user would see in the real world. In terms of your software, the IPD only really changes the distance between the virtual cameras. If you had this fixed at 64mm, a person with 67mm IPD would feel like their eyes were too close together. This can cause motion sickness.

Now regardless of the user's IPD, you always align the rendered images with the lenses (so the centers of the images will be fixed at 64mm apart). This is because your eye can be misaligned with the lenses (in the case of everybody without 64mm IPD), but the lenses still make the center of the image appear aligned with your eyes. However, as geekmaster has just said, the further your IPD is from the center of the lenses, the more blurred it will get. So while the lens-centered image always appears aligned with your eyes, it does get blurry if your eyes are not aligned with the lenses.

i finally understood.
Projection calculation which uses Lens separation distance compensates error that comes from lens center not lying on projection frustrum's axis.
and IPD makes you feel like in that virtual space, by reconstructing virtual word's Ipd. Virtual world's ipd may differs what content you want to show. for example 1 unit is one meter, so be it, as sdk doc says.
Hope i understood correctly. thanks sftrabbit and geekmaster.