- [Instructor] I'm going to be talking about continuities,
and I'm going to use curves to show you
what a continuity is, between adjacent elements.
And this is the same for surfaces.
It's just easier to show using curves.
I'm also going to use a tool called Porcupines
to really show you exactly what's happening
with those continuities.
So, we'll be talking about these tools
later on in the course, but I'm just going to use them here
to show you what continuity means.
If I look at this end, where these two curves come together,
you can see that I have a quill, and another quill,
that are parallel.
At this endpoint I'm showing a tangent condition,
meaning that the slope vector at the endpoint of this curve,
and the slope vector at the endpoint of this curve align.
So, I have a smooth condition, or G1.
If I go to the other end, I have what's called
a G0 condition.
And this is obvious because the quills do not line up.
They're not parallel.
And because of that, the positional continuity is held,
meaning G0 is held, at those two endpoints,
but it's a hard corner.
So anytime you see something like this,
it means you have a hard corner.
The other end is tangent, meaning it's smooth,
but because it's just a simple tangent condition,
it's something that may not be pleasing to the eye
or aesthetic when creating a Class A surface.
Especially if it's something really shiny,
this is something you really see.
I'm going to double click on the spline.
And you'll notice that for this point
it's set to tangent.
I'm going to change this to say curvature.
And you'll note that as soon as I go to curvature,
this is what's called a G2 condition.
Across that point, there's a radius from the first curve.
And across that point this second curve now shares
that same radius.
It means, in this case, that the two endpoints
are G0, they touch, they are tangent,
meaning they have the same slope across that point,
and they share the same radius across that point
from one curve to the next.
Meaning that it's smooth.
So this is going to give you an aesthetically pleasing
condition across the boundary between these two curves.
And this same, again, is held true for surfaces.
When you're doing surfaces on an exterior body panel,
you may need to do things like accelerate that curvature,
as you can see here, I'm accelerating it,
because I want even a smoother transition
across that boundary, going in to what's called G3.
That G3 is the rate of curvature plus acceleration.
So, everything that you see on an exterior body panel
with large, flowing surfaces is going to have the G3 condition.
When we're talking about tighter areas, smaller areas,
maybe things in the interior, then G2 is acceptable
if it's going to be something with a grain, maybe something
that has not quite as bright or shiny a finish
or wrapped in foam, G1 maybe with some acceleration,
like a conic or something along those lines,
would also be acceptable.
Again, if it's a small blend or small fillet
or tiny little areas, and it's an interior,
a lot of times a G1 condition is just fine.
And again, you can get away with using a conic,
even though it may not be perfectly G2,
it sort of fakes the G2 condition.
So as you're designing things, it's very important
to always consider what's happening to the shape
of that curve,
and that continuity.
So, once again, I broke that curvature,
I brought it back down to tangency, these are parallel,
at the opposite end.
This is G0.
This is simply touching.
And once again, if I come in here and impose that tangency,
and impose that curvature,
you can really see that shape change across that boundary.
So, a very important aspect of Class A Surfacing
is making sure you have the right boundary conditions,
the right continuities across those boundaries,
of your primaries, going into your secondaries,
going into your tertiaries.