There's a merged pull request on the void-packages repository

Field3D: fix license
https://github.com/void-linux/void-packages/pull/35042

Description:
From the [homepage](https://github.com/imageworks/Field3D/wiki/Field3D-Home):
> # License
>  Field3D is distributed under the New BSD License.

Looking at the COPYING file, it's clauses (distribute notice in source, in binary, and don't use their name to promote stuff) make it a BSD-3-Clause license.