I do think 100 man years is an exaggeration, or maybe they're talking about fully reverse engineering an existing CAD kernel and all the weird proprietary exten

I do think 100 man years is an exaggeration, or maybe they're talking about fully reverse engineering an existing CAD kernel and all the weird proprietary extensions it supports. In my uninformed opinion working with meshes is hard. In the interest of comparing apples to apples I'll compare a CSG-based approach (joining two mesh objects together) with an SDF-based approach (joining to SDF objects together). If you want to merge two mesh spheres together you need to do a lot of work. First you need some way of telling whether a point is inside or outside of another mesh. This is because you need to be able to delete all the vertexes/points/faces that are inside the other mesh. So you do that, and you delete all the points/vertexes/faces that are colliding with the insides of another object. Then you need to stitch the two meshes together. This is a whole thing, you need to find the boundary where the two meshes would have collided, create a bunch of new edges along that path while also taking into account where the existing faces on both objects are going to be. There's a lot that can go wrong during this as well, it's possible for your geometry to be "non-manifold" which means it has no clear inside or outside, and it's really easy to accidentally make an object non-manifold when you're stitching it together with another object. There are issues where sometimes meshes look alright but in reality there are two edges on top of each other, or a face with zero area, or all kinds of crazy stuff. Making a tool that can reliably stitch two meshes together is a pretty big challenge. Than you start talking about adding fillets to vertexes, and how that affects the mesh geometry of other attached faces, and you're having to write some really complicated error prone code for N different combinations of situations. Like what if the chamfer abuts another chamfer? What if it abuts a spheroid? A bunch of edge cases (heh) depending on the faces that your edge butts up against. With SDFs you just check if the point is inside one object or the other, and than re-generate the mesh from scratch. You write one not-too-difficult mesh algorithm and everything else is basically just OR/XOR/AND-ing things together. It makes defining geometry geometry about as simple as possible, just write a function that can say whether a point is inside your geometry or not. Something you need to be able to do for mesh based CSG anyway, but with a bunch more complications. This is also why tools like openscad can't do fillet/chamfer joins after 10 years and the tool I threw together in a few weeks can. https://github.com/traverseda/PySdfScad https://github.com/traverseda/PySdfScad