Tips and Troubleshooting - 3D File Size

A 3D save can be a few megabytes or it can be a gigabyte, and the difference is almost never the cubes. It is the readouts — the cube letters, the locations, the measurements, and above all the angles — because every character in them is written into the file as a real 3D shape with its own corners and faces. This page shows what a full save costs, where that number comes from, and what to turn off first.

What a full save costs

These are real saves with every option on the export card checked, measured at three cube counts.

Two things stand out. Angles multiply fastest. Every cube reads an angle against every pair of the others, so four cubes carry 12 angle readouts and twelve cubes carry 660 — fifty-five times as many, from three times as many cubes. STEP costs about nine times what OBJ does for the same scene. It writes each shape as a solid a CAD program can build on, spelling out every corner, every edge between corners, and every loop of edges around a face. That detail is what makes the file usable in CAD instead of a loose heap of surfaces, and it is why it is large.

How the numbers were measured

Each row is a scene built exactly as the app builds it: n cubes, a measurement for every pair, and an angle at every cube for every pair of the others. Every option on the export card was turned on, the scene was written out in all three formats, and the finished file was measured. Nothing was estimated or scaled up from a smaller case.

Before it writes, the app does a lighter version of the same count: it adds up the corners and faces in your scene and multiplies by what each format spends on them. A solid model spends far more per corner than a plain mesh, because of the edge and loop information written around it. Against the real saves above, that estimate lands within about a seventh of the true size — close enough to warn you before a large file is written rather than after.

The size warning

If the file is going to be large, the export card stops and tells you roughly what you are about to make, and offers Explain This To Me (which opens this page), Change What Is Included, or Write It Anyway. Nothing has been written at that point, so backing out costs you nothing. The size is quoted in the format you asked for, since the same choices come to very different files in each. A four-cube save with everything on never trips it; a twelve-cube solid model always does.

How to keep a save small

In the order that saves you the most:

• Turn off Angles. By far the biggest saving at higher cube counts — angles are most of a twelve-cube file on their own. Leave them on only when the angle readings are what you are exporting for.
• Turn off Measurements. Each one is seven lines of text rendered as shapes, one for every pair of cubes.
• Turn off Cube Locations. Two lines per cube, and the coordinates are in the TXT report anyway.
• Choose OBJ or USDZ instead of STEP unless you actually need a solid model to build on. If you only need to look at the shape, or bring it into a mesh tool, the plain mesh is roughly a ninth the size.
• Export fewer cubes. Remove cubes you are done with before saving. Because angles grow with the cube count cubed, dropping from twelve cubes to eight cuts the readouts by nearly three quarters.
• Save the shape alone. Solid on, everything else off, is a small file at any cube count — the shape through your cubes has only a handful of faces however far apart they are.

If you want the readings but not the bulk, save a small 3D file for the shape and use Save TXT for the numbers. The report carries every distance, angle, slope, and pitch in full precision and weighs almost nothing. See Action - Save Your Data (TXT, SVG, 3D).

If a saved file will not open

Many programs refuse or stall on very large files even when they are written correctly. If a save will not open, try the same scene with the readouts turned off — if the smaller file opens fine, size was the problem, not the file. Solid models are the usual culprit, since they grow fastest.

See also Concept - File Types and Tips and Troubleshooting.