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Hi, this is Michele Bousquet, CheckMate Ambassador at TurboSquid.
In this video we're going to talk about holding edges
on subdividable models. Holding edges are
edges added to a model to help it keep its shape during subdivision.
You can see the importance of holding edges
by starting with a cube. Here there are no holding edges,
it's just the edges of the cube. And when you subdivide it,
it starts to take the shape of a sphere. More subdivision, and it just gets more and
more like a sphere.
If there are holding edges on the cube,
as there are on this one, when you subdivide it,
the cube keeps its shape.
For a sharp crease or edge on the object,
the holding edge should be very close to the defining edge.
If you want a smoother and more rounded transition between
these two sets of polygons, you can move the holding edge further away.
Anywhere where you have a set of polygons
at an angle to another set of polygons and you want to be able to control
the sharpness of the angle between the two after subdivision,
you will need holding edges.
On this model of a toy tree, we have holding edges around
the edges of each section. This is what it looks like without subdivision
and then when we subdivide, the tree is still keeping its shape,
it's just smoother. On this model,
the diamond shapes need holding edges in order to hold their shape.
The way they are now, when we add subdivision,
the holes start to become round.
And, this is the new topology with holding edges.
Note, that it has edges that are reconfigured around the hole,
so it has the same arrangement of edges from one point to the other.
There's also another set of holding edges just beyond that,
and that helps to keep the surface flat during subdivision.