From 5ab8c6a07c1c92980db33c7493724df757769c8b Mon Sep 17 00:00:00 2001 From: Joe Ardent Date: Tue, 10 Jan 2023 13:49:43 -0800 Subject: [PATCH] checkpoint --- .../sundries/a-very-digital-artifact/index.md | 34 +++++++++++++++---- 1 file changed, 28 insertions(+), 6 deletions(-) diff --git a/content/sundries/a-very-digital-artifact/index.md b/content/sundries/a-very-digital-artifact/index.md index a2b4fa9..fa9fd9c 100644 --- a/content/sundries/a-very-digital-artifact/index.md +++ b/content/sundries/a-very-digital-artifact/index.md @@ -54,22 +54,44 @@ shop: > > *Me*: That's totally fair! I'll get you some files in a few days. -As you can see, I leaned even harder into the bluff; my next communication with the shop was nearly -four weeks later. But that's getting ahead of things. +"I'll get you some files in a few days," was an even harder lean into the bluff; my next +communication with the shop was nearly four weeks later. But that's getting ahead of things. # Meshes and solid bodies First off, let's talk about file formats and how to represent shapes with a computer.[^math-computers] I said I could provide an *STL file*. [STL](https://en.wikipedia.org/wiki/STL_(file_format)) is a pretty bare-bones format that -describes the outside surface of a shape as a set of many, many triangles, each of which is described -by three 3D points. This format is popular with 3D printers, which is how I became familiar with -it. +describes the outside surface of a shape as a set of many, many triangles, each of which is +described by three 3D points, forming a "mesh" in the shape of the thing you're modeling. This +format is popular with 3D printers, which is how I became familiar with it. -This type of representation is easy to create and read, but it's not great for manipulation. +This format is simple to implement and easy for a computer to read, but if you have a model in that +format that you need to manipulate, you won't have a good time. In order to actually do things like +change the shape of the model, it needs to be converted into a CAD program's native representation +of a "solid body", which is pretty much what it sounds like: a shape made of a finite volume of +"stuff", instead of an infinitesimally thin shell enclosing an empty volume, which is what the mesh +is. + +In order for the CAD program to convert a mesh into a solid body, the mesh must be *manifold*, +meaning, no missing faces (triangles), and with a clearly-defined interior and exterior (all +triangles are facing in one direction relative to their interior). When there are no missing faces, +it's called "water tight". You can still have "holes" in a mesh, like if you have a model of a +donut, but the surface of the donut can't have any missing faces. + +The CNC shop had requested a model in a format called +[ST**P**](https://www.fastradius.com/resources/everything-you-need-to-know-about-step-files/). `.stp` +is the extension for a "STEP" file; STEP is supposed to be short for "standard for the exchange of +product data", so someone was playing pretty fast and loose with their initialisms, but I +digress. But the main thing about STEP files is that CAD programs can really easily convert them +into their native internal solid body representation, which allows easy manipulation. + +But so far, I had nothing at all. Time to get some data and see if I can turn it into a model. # Public data + + ## From space? ## Thanks, California state!