Outline for Today
Midterm prep and Chapter 6
Administration
Today
For Next Meeting
Wiki
Link to the UR Courses wiki page for this meeting
Media
Transcript
Audio Transcript
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So I have A slow
network. You
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opposite. So how was your break?
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I feel broken. That's how my
break was.
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It's
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yeah,
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no windows is poorly optimized,
but I know Windows is poorly
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optimized,
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like mine graphics thing, so I
don't really have a designated
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graphics to
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be designated for anything.
Mine's
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poor still running, still
running, it
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still works. Just replace,
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yeah, those are good.
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It was like a 19 $100,000
machine, so at this point,
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wasn't like, and then I've
upgraded price wise, works for
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pretty much everything. It won't
update Windows.
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I'm kind of happy that is
actually good.
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Music. For other things, it can
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be it's been a bit of a whole
new chips, pbrt running
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on my machine a whole do like
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I'm just gonna look at the code
as you
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change GDR
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testing, and
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I'd rather focus on the 15%
return and the reason being,
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works better than
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complete. And the reason being
is four
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used, kind of like, I Just
understand we're actually, like,
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video just past session. I
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it. So any questions about the
assignment that's due tonight?
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Are there any specific kind of
like textures that are kind of
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like required because, like,
I've used a plastic texture for
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like one, and we use like a
bubble kind of texture, a bubble
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kind of texture
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for the other. So is there any
specific
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requirement? No, yeah, I asked
you to do different materials.
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So the network is not
cooperating with me. Even on my
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phone, it's got a weak
connection. So I'm going to I
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switch to version on My laptop
here I'm
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so that'll give you a look at
what I was planning to talk
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about today.
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Give me a second. Okay, I
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about, Does anyone else Having
network problems?
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I Don't know what I cool.
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I did a calendar of fractal
images, or I edited it all. Here
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are the links.
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So I guess with my local, hosted
version, I'm trying to access a
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CSS file that's on the web
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and it's not happy.
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I think you might need to
outline your text. I
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I need to, I
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need to move this, the CSS
that's caused me the problems.
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Make a local copy. I doesn't
like
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that. Never had this problem
before. Every
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single person
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gives us the background was
titled
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in your Text, glitter.
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I wish. I wish people remember
pixel. I
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Where do you get the fractals
from? Can I get a copy of that
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one I
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yeah, I've been meaning to put
the large scale resolution ones
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up, so I will do that.
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This is from 95 I
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think so. This is a van Cook,
snowflake curve I
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spend it over a height field.
This was Ray tree and
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networks back.
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Maybe, let's
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Okay, so this is The assignment.
So we're using materials.
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So the main sphere starts out
being with the dielectric
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material. So add two more
spheres with different materials
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and
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Okay, are there any other
questions about the assignment
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then my post yesterday,
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answer some questions I didn't.
There was no reply to it, so I
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wondered.
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So I thought better of getting
into chapter six stuff today
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based on the conversations we've
had online. So I just focused on
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the
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the midterm that's coming Up
next Meeting I
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in Section chapter one, section
two
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introduces a lot of ideas that
we're exploring This semester. I
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so they talk about the light
transport equation, also known
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as the render rendering
equation. I
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So, what is the purpose of the
rendering equation?
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What exactly was the question?
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What is the purpose of the
rendering equation?
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Total, realistic rendering. I
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let's say it's to do with
simulation as well.
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So An indistinguishable
simulation. I
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So we're dealing with
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light in the scene. Well,
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so this video doesn't have any
sound. It's about Three minutes
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Long. I
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information, Please Do
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the best.
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Practice your playback Speed up
really High. Oh, my
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God. It kind of like, because
the SDR does not kind of like,
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connect like correctly, whatever
does that kind of like
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accelerates it to some example,
what
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you're
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saying is my cable might not be
connected. Yes, does.
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If it wasn't connected properly,
wouldn't be able to see the
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picture on the screen. I
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I mean, if my phone is plugged
into a charger, it can still
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charge. If it's not plugged in
properly, it's just it will
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charge slower. I
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THE END seems to be the right
speed. I
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here's the Wikipedia entry that
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maybe gives A bit
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more accessible presentation and
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so the idea is, we're looking at
the point x and seeing the light
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that gets emitted from that
point x in the direction and
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W, o,
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so we're dealing With the con
looking.
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I so why isn't,
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let's Say, four samples per
pixel. I
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What's that? Number 4096,
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yes, power,
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I mean, n samples. It's just
like when you're doing
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statistics, you make more
variance and stuff when you have
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a small sample base. So, yeah,
that's why you choose a second
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to 30 should which should Set
End to 30? I?
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It so
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it makes sense. The four samples
per pixel is going to be as high
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quality As 4096 samples per
pixel.
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What are some of the particular
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challenges, if, if we have four
samples so,
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oh, you showed us the outer
gamut pixels. So I imagine
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there'd be way more of those. I
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so all light Sources may not Be
counterpoint.
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At some point improvement you
Get from adding more samples,
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but
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so if we look at Like the Image
tool diff, we'll see the images
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getting the subsequent images
will have less variance, and
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then when they're threshed, the
variance is below a threshold,
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We can say
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this is a good number of samples
per pixel to use And
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yes, I Excuse me, Please Do
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the idea was, they're supposed
to open In Order. I
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so this is the realistic camera,
and I'm setting the shutter. The
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shutter open time is zero, and
the shutter closed. Time is
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starting with 1234,
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so that's shut or close At 10
and a 20 and a 3040, 50 and
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60, 7080, 9100, and that's 200
And it 200 seems like it's
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overexposed. You
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it almost seems like it's a
percent, like at 100% it looks
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good at 200% it looks 200% is
bright. Like, too bright. It's
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yeah,
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I'm not sure what the units are
on that time.
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Usually they're about, like,
some x over like a fraction of a
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second. So like, you have, like,
one over 60 is the 60th of a
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second. And then if you have
like, a time two, that would be
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200 over 100 so I'm assuming
this is about 100th of a second
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increments. So that'll be two
seconds of exposure for the last
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one,
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unless you added it like
aperture, but
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what it's doing is it's adding
all the light in that time. So
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just we see stuff, and then we
keep refreshing our vision,
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whereas it's just like, what if
we add all the light from the
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last 200 milliseconds together?
This is what it would look
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like. Well, I mean, our eyes do
the same thing, though. It's
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like a running average. You
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and so I think it's percentage
and average, right?
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Do? Okay, so David had a
question last day, I believe,
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before the break,
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about why changing the position
of the camera didn't make sense.
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I don't have a phrase. It was
weird. The
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behavior was weird. Yeah, I
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so can you look at this input
file and see what might account
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for that weirdness? I
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camera.
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Perspective, perspective,
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so using
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perspective, yes, it's
perspective. So we have a
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viewing frustum that's a
truncated pyramid. So
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that changes to the camera
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would have to be normalized
before we'd be able to properly
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use the perspective.
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Explain that please. What
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do you mean for putting in any
vectors
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and stuff that we're putting in
different cameras we're putting
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in one particular view, so we
need to normalize it to be able
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to get it to be proper to the
actual field of view and The
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world of you, in regards to your
frame, You
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so
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let's think about the camera
frame
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how
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So a common and straightforward
way to specify the camera frame
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is to the to specify an eye
point that's where the camera
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position is going to be,
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and then a look at point, the
point you're Looking at, and
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then another vector so the eye
point look at point defines one
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axis of the cord of the camera
frame your out
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vector is usually
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defining another one. Yeah. So
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when we specify look at or the I
point, look at point. That's one
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vector of our coherent system.
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But we can still it doesn't
fully specify the frame, because
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the up vector can rotate around
that, that I point look at point
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vector. So once we fix the up
vector, so we have to look at
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the i point, look at point
vector, the up vector, and then
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we can find the third vector by
doing a cross product between
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these two vectors. I
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call that on the right vector
personal
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reference. Okay.
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So how have we defined the
camera frame in this sample
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input file? Well,
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we set up, but we're also
supposedly like, aren't we
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looking down? I'm confused,
because the I is above the
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lookup point, so we should be
tilted downward. So we're
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declaring up as one, one. I
guess that's so
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the up vector is, is more so,
like, it's like, you have,
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literally, an arrow pumping up.
You have an i, which is just a
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point, yeah, it's like, you draw
a string between here the camera
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relative
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to the Office of z, it's in the
third slot
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and one. So you just, yep,
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that's, that's the thing, yeah,
when we change the Z, it moved
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backwards, or, like, it moved
upward. And I'm like, that's
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weird. That's the reason, right
there, we're declaring what the
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z is, our up. So that is our Y,
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yeah, in
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a lot of 3d space, they use Z is
their up axis, as opposed to y.
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I would say y is usually the up
vector.
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It's more common, but I've
actually been reading about
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this, oddly enough, over the
break, of people using the Z as
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the upward vectors the third
axis, yeah, the third axis
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becomes up because it's now, no,
it's leaving the plane,
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therefore it's adding the up.
That's the way I've seen it a
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few times. I actually this makes
a lot of sense, but they're just
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using it that way. It kind of
seems arbitrary. Honestly,
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I so if we switch the numbers
from those two columns, it
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should fix it for us, at least.
Yeah,
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you'd also have to change where
the light source is as well to
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make it relative to us.
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That the Y in that file, yeah,
so I've changed it here, just it
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might be a good idea to change
the light source so that the The
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Y is 100 and The Z is 40. I
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Let's do this One First and
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any ideas about how it's just
going to Look. I
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feel like the light might be in
a weird spot, but hopefully it
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works. Oh,
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it looks cool.
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Is it has we then changed the
world plane, where the like
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world where the world plane is,
because all those coordinates it
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was given were relative to
having the Y as one axis and the
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Z is another. That's why I was
saying we should swap that line
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value. But if it's doing it for
all the coordinates, you have to
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make sure you're at least
consistent on everything.
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So so the simple pbrt file would
be doing it in a different
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direction too.
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I that'll just move the light
though You have to do both the
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checkerboard, the ball and any
other elements. Let's see what
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this test first. It's just gonna
move the light,
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which might look cool.
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Yeah. So now the lights casting
the shadow downward, because
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that's the good fraction We
switched. Now the ground was
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down there. Okay, okay.
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Yes, you have to change it for
every single thing. So I think
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it's just better to accept the
fact that it's using a different
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system than wait a second,
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it's got a translate
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function. It's translating,
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if we got rid of that,
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fix everything, zero,
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minus 101, negative one. But it
would have to be zero, negative
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one, zero. But then you see
those points. They would also
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like, would they a translation?
Is not a multiplication. It's
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not, it is not, no, it's just
moving. It's like, it's saying
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we moved it down, or, in this
case, to the left. And then all
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points are relative to that. So
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everything's relative.
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Say that. Why wouldn't we just
wouldn't we just move the
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cameras to one model view or one
view?
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Anyways, that's what I'm
hammering saying. Everything was
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in X, Z, Y, essentially. And so
rather than switch everything,
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should accept that it's using an
alternative format.
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So if
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I were making a file from
scratch, I would definitely do
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X, Y, exactly.
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I mean, choice of coordinates
are
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kind of arbitrary. It is, it is
arbitrary. It's just you have to
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know what it is, see, that's
what happened. That's exactly
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what it's expecting do.
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Making sense
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actually looks pretty cool.
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Texture mapping over here is
suspect
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that's actually pretty cool.
It's nice. It's nice to go
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Yeah, every single one of those
points you'd have to go like
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negative 20, zero, negative 20,
anywhere that there's a, x, y,
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z, you'd have to switch the last
two,
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unless they're identical. That
is, and then, yeah, obviously it
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excludes things like RGB, which
are not vectors. Per se, I think
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the problem we're having is
because of the setup. The other
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way, yeah, exactly because I'm
saying, rather than change all
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the values, it's just might be
better to accept it for this
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file, any subsequent files we do
make, we can set to whatever.
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No, we were trying to modify
this last week. Yeah. Sorry. So
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the problem we get this got
brought up is because it was a
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problem because it wasn't
working as We expected it to.
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Yep, Now we Know why you
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Fix the texture And
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now the lights still in a weird
position, that's why the shadows
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off the side, but now it's a
sunset, so that's Cool. Look.
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So any other thoughts about the
exam?
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We're mainly focusing on the
stuff we discussed in class, as
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opposed to like, what do files
and pbrt look like? Is that
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correct? Or will there be some
asking about the file structure
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and stuff like that?
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I I think I could ask a bit
about that.
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Will you, since today's quiz was
all about midterm questions,
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will you be sending out the list
of the midterm questions? And
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people suggested
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Yes?
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How? Much of the midterm will be
based on questions that people
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have suggested I
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there won't so I would say that
there's five chapters, two or
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three questions per chapter. I
don't want anyone
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to hurt themselves writing, so I
will take them as input.
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So the questions will be based
on your input and my sense of
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what are interesting,
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not just interesting, but
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maybe will be a bit deeper than
what's been suggested. So I get
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a sense that you understand the
concepts.
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Does that make sense?
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Will they all be short answer?
Will there be a mix of short
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answer, multiple choice?
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I'll see if I can put in a
multiple choice where two space
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questions like transportation
matrix.
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There Yeah, I'm not
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a lot of those you mentioned
earlier in the semester. It's
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more about learning the
concepts, yeah, the details
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of of everything.
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Is that correct? Yes. So I was
going through, I was going to
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put the links to the Wiki pages,
but there aren't any. I thought
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people were signing up and it
was going they just people just
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didn't post the class
discussions list. I was wrong.
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You
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Any final thoughts, yes, how
long do you expect the start to
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finish
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for you or for everybody else?
The slowest
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person, I would hope it would be
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such that you have time to
comfortably review your answers.
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And I'll commit to saying
between 10 and 15 questions.
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So you'll send us, I would
assume you'll be reviewing and
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sending lists today
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or tomorrow. Yes, the last 30
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minutes. Yes, although maybe
you'll be done in 10, I don't
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know.
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Thank you for today. I'm gonna
see about resolving these
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network issues once and for all.
Responses
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