# Equivalent of emptymesh in 3D

**URL:** <https://community.freefem.org/t/equivalent-of-emptymesh-in-3d/4171>\
**Category:** General Discussion\
**Created:** [December 28, 2025, 4:50pm UTC](https://community.freefem.org/t/equivalent-of-emptymesh-in-3d/4171 "2025-12-28T16:50:56Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![pi.3.141](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@pi.3.141](https://community.freefem.org/u/pi.3.141)\
**Post date:** [December 28, 2025, 4:50pm UTC](https://community.freefem.org/t/equivalent-of-emptymesh-in-3d/4171/1 "2025-12-28T16:50:57Z")

</div>

Hello Freefemers,

Emptymesh command is very useful to handle boundary values in 2D. For example

```auto
mesh Th=square(10,10); 
fespace Vh(Th, P1);
Uh u, uh;
mesh Thb=emptymesh(Th);
fespace Uhb(Thb, P1);
Uhb ud=x, un=y;
problem laplace(u,uh) 
= int2d(Th)( u*uh+dx(u)*dx(uh)+dy(u)*dy(uh) )
- int1d(Th,1,2) (un*ub)
+ on(3,4, u=ud);

```

I am looking for an equivalent of emptymesh functionality in 3D. From the documentation, I would expect that the extract command may provides the same functionality. Can anyone confirm this, and eventually provide any piece of code how to implement it?

Thank you!