@jackfirth @ntoronto
There are many ideas that I really like about what pict3d allows you to do with positions and directions.
http://pkg-build.racket-lang.org/doc/pict3d/vector.html
For example, it allows translations, rotations, scaling, etc. to be expressed as transformations, which can be composed and (if mathematically possible) inverted, and it also allows transformation combinators like relocate and local-transform which can be powerful and intuitive tools for dealing with multiple coordinate systems, etc.
I think pict3d does a great job of providing a good posn library for 3 dimensions, and I think it would be great if this 2 dimensional posn library could use some of those ideas.