# Creating a Surface Between Two Curves.

The curve through points A, B, C, and D is defined by a parametric function

`a(t)`

.
The curve through points E, F, G, and H is defined by a parametric function `b(t)`

.
The idea is to "stretch" the surface from one curve to the other, which is the purpose of the `u`

parameter.
The `u`

parameter varies from 0 to 1 (or in this app, 0 to `c `

which varies from 0 to 1). When `u = 1`

, the surface is all `a(t)`

. When `u = 0`

, the surface is all `b(t)`

. When `u = 0.4`

, the surface stretches 40% of the way from `b(t)`

to `a(t)`

.
The parameter `t`

varies from 0 to 1 for splines. This can vary as freely as you like.
This is the command:
`Surface(u x(a(t)) + (1 - u) x(b(t)), u y(a(t)) + (1 - u) y(b(t)), u z(a(t)) + (1 - u) z(b(t)), t, 0, e, u, 0, c)`

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