- [Instructor] A very important tool
you need to familiarize yourself with
is called Porcupine Curvature Analysis.
You can analyze the shape of curves with this tool.
Now, for this file, you need to download
your file references and open it up,
called porcupine, and let's get into it.
With the porcupine curvature,
you pick the curves or surfaces that you want to analyze,
and as you can see here, I have a whole chain of these.
And this chain is showing something very different
across the entire spectrum of Porcupine analysis.
With this tool, you can verify the radius
or the curvature, and the differences between the two is
the curvature shows the actual curvature,
or the radius shows the inverse of the curvature.
Why this is important is because the curvature
on tighter curvature curves is going to show up more,
and flat spots aren't going to really show up at all,
whereas with radius, I'm measuring the inverse
of the curvature and it's going to allow us
to analyze our flatter areas a little bit better
versus our areas with more curvature.
So you want to look at both, 'cause there's going to be shapes
that are broad and flat,
shapes that have a lot of curvature.
Now, this porcupine analysis tells us
a whole heck of a lot about these curves.
So you saw me a minute ago playing with the amplitude.
This is basically the length of the quill.
You also have a density.
How many of these do you have?
You also have display options,
which is the maximum radius, minimum radius,
across each one of those segments and curves.
So if that's important to you,
you can pull that information off.
You can also reverse the comb.
It's still performing the same analysis,
but now it's just reversing the comb direction
that it's pointing in.
Sometimes you need to do that, again,
to visualize things a little bit better.
I'll just return it to its normal.
So I'll leave it at radius.
I'm going to select OK, and what I want you to notice is
as I zoom in, this curve comes in, touches,
and you'll notice that the porcupines
are not parallel at the very end points.
This is telling me that this is G Zero.
If I come across to this point here,
you'll notice that these two are parallel,
but they're different lengths.
This is G One, or tangent.
So these quills are describing to me the shape.
Come across over here, and you'll see in this case
I have tangent condition, I come across to this end,
another tangent condition, but you'll notice
right before I get to this curve, I have an inflection.
This is telling me that there's a reversal in curvature
on that spline.
And this is something that porcupine analysis,
as you can see, is really going to show.
You may not see that with the naked eye,
but because of the way the analysis is viewing the curve,
now you can see these inflections.
I'm going to double-click on this curve,
and across point one, I'm going to go Show Parameters,
and go to Curvature.
Once I go to Curvature, you'll notice
there's a radical shape change on that curve.
I could increase the tension, say on both ends,
and as you can see, at this end,
I have a curvature continuity.
I know this because the quill is the same length
at the two endpoints of those curves.
This is telling me that, as I transition
from one to the other, I have a very smooth shape.
And here's another inflection, as I come across,
here's another inflection, and here I just simply
have a G One continuity across that boundary.
So now I'm going to change this to Curvature.
And as you can see now, those quills are the same length,
and the inflection point's moved further back,
'cause now I have some of this curvature
coming off of this next curve.
Select OK.
I'm going to come back over to this curve,
and double-click on it.
And once again, as I start making modifications,
this is this end, this is .2.
I'll say Curvature, there's my inflection.
I can also remove that tangency at that endpoint,
and you can see here those quills no longer parallel.
That means this is G Zero.
That's what I mean by critical to understand
what the porcupine analysis is telling you.
It's going to help really describe the shape of curves,
boundary conditions from surfaces.
This is going to graphically display to you what's going on.
Now, earlier I spoke about the connect checker.
Connect checker is doing a mathematical comparison
between curves and surfaces, this is a graphical,
true visualization of what's going on
between curves and surfaces as well.
So get familiar with a porcupine curvature analysis,
and as you go through and you use the tool
over and over again, you'll find that you really
can't do anything highly stylized without it.