Mtg 6/26: Thu-23-Jan-2025

Outline for Today

Geometry and Transformations

Administration

• Happy Thursday
• Attendance
• Class calendar for today
• Upcoming events

Today

• Etymology of sine, cosine, and tangent

For Next Meeting

• Take quiz before the start of our next meeting

Wiki

Link to the UR Courses wiki page for this meeting

Media

Transcript

Audio Transcript

• It's so the computing resources at the
• University of Regina are not happy with me lately.
• Does anyone else feel like they're being singled out for
• rough Treatment?
• Let's see if I can find a screen i
• Oh, welcome.
• You said, I mean suspicious activity.
• Got so the one thing I can the edge room I can
• deal with with my cell phones, hot spot. I'm waiting on a
• ticket for that, but the other one last night and today, my
• password manager, so I'm using one password. Anyone familiar
• with that one? I i have a 19 character password, but last
• night, I decided to not accept my credentials. So then I called
• it service, and I have somebody had somebody who was helpful,
• but a little bit condescending.
• And so when it happened anyway? So I reset my password, and it
• seemed to work. And then today, when I logged into your courses,
• I had the same problem, and I called it support, and I got the
• same person and said, if you're confused, I said, Listen, I'm
• not confused. I have anyway. This is an IT person at the U of
• R, Yeah, you sound shocked. I
• didn't know that we had an IT.
• Help. Help Desk,
• but it's the service it's now it's the Service Desk. IT help
• desk. I can't
• believe we even paid for one, but we have one. I worked there,
• but there being an IT help desk. It was like one person does kind
• of check out? Well, there's lots of people in that office. I
• think it'd be funnier that's just like, one day, just sitting
• there, like, all the time, just like, oh, going through set my
• passwords, like, Oh, it's you again. It's the whole
• person that's just like mumbling to back. Like.
• So what I learned today is if I copied the
• password out of the Password Manager and click Login, it
• worked. So I'm I'm not sure if there's a strange character
• somewhere in the process, or this particular person with whom
• I spoke was not interested in my problems with a passive password
• manager. He was convinced that the problems with me,
• the other apartments that are like that.
• Yeah, anyway,
• for sure, it's not limited to my car Statistics.
• Not CS, so we'll say onward and upward. You.
• So I was talking about the comes
• from a bow and arrow.
• Yeah, and
• a mistranslation along the way, apparently.
• Anyway, this gives you a few resources to look at if you're
• interested in etymology. Etymology is study of the
• history of words. Entomology is a study of bugs, so there's one
• letter difference, I believe I
• see if my black marker that I brought is going To be
• any better. So
• So do you agree with that statement? Chapter Three is too
• big to say, just read chapter three.
• Okay, so I will endeavor to break things down so
• we have a bit more depressed. I compressed so we have more focus
• on What we'll be talking About the Next day. I
• so we don't finish in chapter three today, we'll cover next
• day, and then in future, I'll break down chapters by sections.
• So I'm pleased to report somebody came to my office hour
• and somebody posted to the class discussion, and I replied right
• away to encourage that behavior so everyone's got the software
• sorted. Now. Is that true?
• Should we go? Does anyone not
• is anyone not willing to put their hand up in
• class? Who's not willing to put their hand up in class?
• I guess I should ask who's willing to put their hand up in
• class. Okay, I think That's what everybody saw. I
• so keep you abreast of developments, whether we get
• pbrt installed in the labs. I
• so let's talk about the quiz questions and
• it's so appealing to use This mouse, but it's not
• connected to my computer, So
• okay
• quiz, so?
• So where are the two things we have to specify.
• We're dealing with array,
• Origin and Direction. Yeah,
• and to cover the matching question, what kind of
• thing is the origin and what kind of thing is the direction,
• point and vector. Yeah, point and vector.
• So how would you? How do you see the quizzes so far? Are they
• for those who did 315 last semester? Are they better than
• what I did in 315 okay, I
• so generally, the quizzes are tied to the readings. So when
• you're dealing with questions that come up, you can look at
• the readings to find the answers. So it's a way to
• incentivize you to look At the things I've asked you to look
• at. I
• that's not the word I was looking for.
• I that's not quite the question was, I guess
• I could read the question, what is the unfortunate turn of
• terminology with normals not
• necessarily normal?
• Yes, they're not necessarily normalized. Yes.
• I try and do more alliteration. I do
• normally. I
• so what is a stereo steroid in
• I don't understand what it is. I'm trying to figure out it
• seems to be a unit index, but that's as far as I figured out.
• It's the way of like measurement of sphere specifically, it's
• kind of similar to how, when you're measuring like a circle,
• you have like radians, like a PI is like something pi. Radians
• for, like a single, like a whole circle is measured in radians,
• yeah. So if you apply that to a sphere, since you can, like,
• integrate the circle into a sphere, you can turn it into
• stir radians, which is just basically a solid radian. So the
• amount of area that if you project a ray into, like a
• closed loop, makes, like, that amount of steradians.
• Thank you.
• Makes good sense, actually.
• So when we're talking about the in 2d we can think about an
• object, the angle, the arc length of the projected object,
• and we'll maybe see those
• look at a couple figures. So in ve,
• instead of the planar angle, we have the solid
• angle, which measures The amount of the sphere that's covered by
• the
• by the object that's projected. So steradian is a way to measure
• angles within A sphere and
• maybe I fill that in a bit more.
• Okay, so before we get into
• the Text stuff I
• promised A gold sphere I
• looks like a Christmas ornament?
• Does it look like a gold Christmas ornament?
• Though? Yeah, I think so too. So let's
• there are lots of parameters in this description that we're not
• going to deal With today, but I
• so see the
• physically based and
• the parameters at work here.
• So we can see there's a reflection of the
• checkerboard pattern here that's clear enough, but there's about
• 3% of the pixels here that are out of gamut or clamp
• zero to one.
• So let me I me
• show you what the file looks like.
• I just changed the sphere that was the dielectric, or the glass
• sphere, and I made it into the gold sphere.
• I will separate these a little bit better and
• put them on to make them available in the Dropbox. I
• it so it's the same as a
• nose of audio is connected to the HDMI. I
• so I took this material from an example of a gold plated
• kangaroo. We can look at that file in a minute as well.
• So the end, these are spectrum data. So there are files here
• that are referenced for Gold.
• Au is gold and
• So let's try Changing i
• Four. I'm
• so we made the gold rougher so it looks more like an ornament,
• doing it the other way. I
• it so it's a much smoother surface. Does that make sense?
• Yeah, it's really reflecting the sky so heavily.
• So let's see if, what if we
• Increase the samples here. Sorry, Sorry. I
• so this has more out of gamut pixels, so you can see
• here the errors or
• the pixels that are out of gamut and
• so would you want to, like, clamp them to keep them in
• range?
• Well, they do get clamped here. So the report is
• three. That's a little bit less than two or 3%
• but the pixels are
• have been clapped, and
• so that's where we see these specs
• come up. So I
• part of what we'll explore is how to set the
• parameters so we we get
• better images,
• so We don't end up with
• Without of gamma pixels. We
• Okay, so we had Killer root coated Gold. Yes, I
• can you See I should
• change this. I
• Is it first? Visible enough? I
• so what I've done for for the gold, The simple,
• I've taken the
• coded conductor description i
• from here.
• So this is applying the code of the
• conductor to a killer
• room. So Let's I
• up. Let's run This. We're
• it. So once we get through chapter three, we'll
• look at the user guide for the pbrt and understand what's being
• specified in these images, in these files, and how they're set
• up, and then use that For our first assignment.
• I Let's look at the gold one.
• And it look
• like a solid gold compared to the other one I
• yeah, there I was only COVID and
• gold. Yeah, I'm gonna just look At the file now. I
• so this is
• conductor material, as opposed to coded conductor I
• it Okay. What do you think about that?
• Can I see the other one back and forth?
• Should be just down a little bit. I see it there. Says one
• beside it,
• just above your mouse, there's a highlighted thing just above
• that with one, okay, okay,
• yeah, it looks like A golden ring this time, instead of an
• ornament. I
• Okay, so I I
• can see the
• this coded one doesn't Look as
• looks different than The Golden One. Anyway, I
• so I just want to highlight the camera
• implementations in tbrt, so We're using the differentials.
• So the differential is,
• if that's
• one ray going out, then we have the difference
• in x and in y.
• So the rays are going out from the camera one pixel apart. So
• we have this, this one, and then we're talking about using the
• differentials to capture the information, more information
• about The
• the area surrounding the array of that pixel And
• so bounding boxes.
• Have You encountered that idea before? So
• pen is for pen is horrible.
• Maybe I should use it this one, maybe that's going to last a bit
• longer bounding boxes.
• So I just want to think about the general case,
• why bounding boxes might be helpful in processing a scene
• that has billions of triangles in it. We don't have to start
• with billions. We could say millions or 1000s, even,
• well, I can see if, like you're trying to decipher
• array or something, to see if it interacts with that particular
• bounding box at all. I and then if it interacts with that box,
• then, due to further calculations, if it doesn't,
• then you can skip it.
• Was that your answer?
• It was similar. Okay, I
• i have something that could also be added. All the vectors that
• are going upward will probably not collide with anything,
• unless you have a roof. So you can have a similar bounding box
• that's anything that's scattering upward probably won't
• collide with anything. So you can just stop calculating them
• at a certain point.
• You could even, like, clamp anything that shoots up too far
• from The light source. I
• You so we can talk about in ray tracing, that
• we send out the rays from the Camera and we measure their
• interaction if we have a perfectly reflective sphere,
• then we bounce a reflection off The sphere. And if there are
• more spheres, then we create more rays that reflect.
• If we're if we have a model that's very reflective has a lot
• of reflectors in it. At some point we could go on forever and
• so this use of boundary boxes in 3d is discussed later. Another
• example using them In the Software Is The
• that's a question criterion to stop, other than
• depth of weight of race, because, if so number of
• reflections, you could have it stop after a certain amount,
• because we talked about like infinite back and forth
• Reflections, but maybe you don't want more than eight.
• Alternatively, if it's not necessarily the number of
• reflections, but if we assume that a ray is basically just
• like a photon, have a little walk around, there's like a
• predictable curve. It's like the inverse squares. It gets farther
• and farther away. It loses energy. But if it reflects off
• something that's not perfectly reflective, it loses some
• proportion of energy. And you can clamp it so that after they
• lower bound, it just stops computing because there's no
• additional info being added.
• Yes, i
• Does that make sense? I
• so this is the planar angle.
• So that's the angle from a point p of an
• object.
• So from the top to the bottom, that's the angle and S is the R
• length on the
• unit circle the
• so when we have a three dimensional so
• I'm Going to go from the unit circle to the unit
• sphere. Then we're projecting the object onto the unit sphere,
• and then have the total area s of the projection, and that's
• the solid angle instead of the planar angle. And the solid
• angles are measured in steradian
• so we can think of polygons being projected onto a sphere.
• That becomes spherical polygons and
• so again, think About edges of the polygon being great
• circles. I
• so a great circle is one that includes the center
• of the sphere. So it's not just off to the side. That's not a
• very technical definition. And
• so there are a few different spherical parameterizations used
• in the software we can do spherical coordinates and
• so there's two angles and
• one in the plane, the x y plane, and then another
• one In
• the Z axis.
• It's quarter after two.
• So thank you for today, and we'll finish the rest
• of Chapter Three on Tuesday. And then we'll get into using the
• software in more detail. Okay, thank you for your attention
• today. Have a great weekend.

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