File Types

Cattail.Nu SpaceCube writes four kinds of geometry file: SVG, USDZ, OBJ, and STEP. They are not better and worse versions of each other — each one carries a different amount of information, and the right pick depends on what you plan to open it in.

The big idea

Think of it as three questions. Is the thing flat or solid? Does the file carry its own colors, or does the program you open it in supply them? And is the shape just a skin you look at, or a solid a machine shop can build from?

SVG — flat.
OBJ — 3D skin, no colors.
USDZ — 3D skin, colors included.
STEP — 3D solid, no colors.

SVG

Scalable Vector Graphics. A flat drawing, stored as instructions — "a line from here to there" — rather than as a grid of dots. Because it is instructions, it stays sharp at any size, and you can open and edit it as text.

This app writes one only when you have exactly three cubes: a drawing of the triangle they form. Any browser, drawing app, or vector editor will open it.

USDZ

Universal Scene Description, zipped. Apple's scene format, and the one Vision Pro, iPhone, and Mac open natively — tap a .usdz and it just appears. It is a package: the shapes, the colors, the textures, and how everything is arranged, all bundled in one file.

This is the only format here that carries how the scene looks. Choose it when someone needs to view your work rather than build on it.

OBJ

The plainest 3D format there is, and nearly every 3D program reads it. It lists points in space and the triangles stretched between them — a shape's outer skin, and nothing more.

No colors and no textures come along, because programs that use OBJ normally supply their own. It is the smallest of the three 3D files and the safest bet when you do not know what the other person uses.

STEP

The engineering format, read by CAD programs like Fusion, SolidWorks, and Onshape. Where OBJ describes a surface, STEP describes a solid: every corner, every edge running between corners, and every loop of edges closing a face is written out in full.

That is what lets a CAD program treat the shape as real material — cut it, drill it, join it to something else. It is also why STEP files are large, about nine times an OBJ of the same scene. Choose it when the shape is going into a real design, not just onto a screen.

Which should I pick?

Just want to look at it, or show someone? USDZ.
Bringing it into Blender, a game engine, or a 3D printer's slicer? OBJ.
Building a real part around it in CAD? STEP.
Worried about file size? OBJ is smallest, STEP by far the largest.

The two other files

Two more file types are not geometry at all:

TXT — the written report: every location, distance, angle, slope, and pitch as numbers. Tiny, and readable anywhere.
.spacecube — a saved workspace. Not a picture of your cubes but the arrangement itself, so the app can put them back exactly where they were.