Three of our tools measure your own stone as well as ours: the 3D Gemstone Simulator, the Brightness & Tilt Analysis and the Cut Performance Wheel. Open a cutting file or a 3D model with “Measure your own stone”, or drop it anywhere on the page, and it is measured with the same code, at the same settings, as every cut in our library. The file is read on your device and never uploaded.
The files we read
| Kind | Formats | What we take from it |
|---|---|---|
| Cutting files | GemCad (.asc text, .gem binary), Gem Cut Studio (.gcs) | Every facet as its angle, index position and distance. The file says which way is up, and its index gear is shown with the stone. |
| 3D models | STL (text and binary), OBJ, PLY (text and binary), OFF | The triangles, grouped into facets by the plane they lie on. |
| glTF (.glb, or .gltf with its data inside it) | Every mesh in the scene, with its transforms. Compressed meshes (Draco, meshopt) and data kept in separate files are not read: export one .glb without compression. | |
| 3MF | The 3D model parts of the archive, and nothing else in it. | |
| STEP (.step, .stp) | Each flat face as its exact plane. A cylinder, the turned girdle CAD gives a round, becomes a ring of flat facets with the cylinder’s cross-section area. Any other curved surface is not read. | |
| FBX (binary and text) | The mesh. Its model transforms are not applied, so a stone exported with a stretched scale is measured unstretched. |
A file can be up to 32 MB. Size and units do not matter: every tool measures the stone’s shape, and the simulator sets its size from the carat weight you choose.
Getting a file that works
- A cutting file is best. GemCad .asc and .gem and Gem Cut Studio .gcs files describe exactly the facets a cutter cuts, and say which way is up.
- From a 3D program, export the stone alone. Hide or delete the setting, the stand and the floor first, then export only the stone as STL, OBJ, glTF (.glb) or STEP. In Rhino, Blender, SketchUp, 3ds Max, Maya or Fusion 360, use Export: their own files (.3dm, .blend, .skp and so on) cannot be read by a browser.
- Downloads from model sites such as Sketchfab usually arrive as a zip. Unzip it, then open the .glb if there is one. A .gltf that comes with a separate .bin file cannot be opened on its own, because a browser opens one file at a time: download or export the .glb version instead.
- No compression. Export glTF without mesh compression (Draco or meshopt).
- Many models are made to look good, not to be cut. A rounded, smoothed or scanned stone has no flat facets to measure, and some display models are not closed. For those, a cutting file of the design is the way to measure it.
- On an iPad or iPhone, a file in iCloud Drive, Google Drive or Dropbox may need to download to the device first; if it will not open, save it to Files and choose it from there.
What a file must describe
One closed, convex, faceted stone. Anything else is refused with a sentence saying why and what to do, rather than measured wrong:
- One piece. The file must hold the stone alone. Models made for display often hold more: the stone in its ring or prongs, a stand, a floor, or an inner copy of the stone that some renderers use for refraction. We count the separate pieces and tell you how many we found.
- Closed (watertight). The surface must enclose a solid, with no holes: the solid its facets enclose must be the solid the model encloses, to within 0.5% of its volume. A hole, or a facet set that never closes, is refused.
- No inward corners. Every tracer here follows light through flat facets that all face outward, so a heart’s notch or a concave pavilion cannot be traced. A point of the model may sit no more than 0.1% of its size outside any of its own facets (0.2% for STEP, whose CAD exports stitch facets less tightly).
- Curved or scanned models. A cut stone has flat facets. A model that breaks into more than 2,000 flat pieces while it is read is a scan or a smooth shape, not a cut.
- More than 400 facets. The most we measure in one stone.
How we read it
The file is read by a small program running on your device, separate from the page, which is stopped as soon as it answers, and after 20 seconds at most. It turns the file into the stone’s facets, each a flat plane, and places the stone the way every cut in our library is placed:
- Which way is up. A cutting file says. A 3D model does not, so it is stood on its largest facet, which on a cut stone is the table. If that is wrong, “Turn it over” flips it.
- Which way round. A stone drawn square to its file’s axes keeps that. Otherwise straight sides are squared up, an elongated outline lies along its long axis with a pear’s point to one side, and a round turns so its largest crown facet faces the same way as our T73.
- Level and upright. A facet within 0.06° of level, such as the table, or of upright, such as the girdle, is set exactly so. GemCad writes a vertical girdle as −89.99°, and models carry rounding noise.
Depth, table and length to width are measured as for our cuts: across a round’s girdle corners, and across the width of a fancy or step cut.
What each tool does with it
- Brightness & Tilt Analysis. The same trace, grid and figures as for our cuts, described in Brightness & Tilt Analysis. A stone with more than 96 facets, common when a 3D model cuts a round girdle into thin strips, is measured in full and drawn by a larger version of the renderer.
- 3D Gemstone Simulator. The stone gets the same cut data our build writes for our own cuts: proportions, girdle and culet measured from its facets, and for each gemstone the share of the pavilion steep enough to reflect head-on light. The crown angle is the tier that meets both the table and the girdle, and the pavilion angle the tier that runs to the culet. These are measured, so a design that names a different tier as its main can read differently from its diagram. The stone is shown exactly as the file describes it, with no cut grade, and the PDF report includes its brightness and tilt analysis.
- Cut Performance Wheel. The stone is scored by the same light census as our cuts, described in Cut Performance Wheel and cut-page scores, with the same fixed sampling, in all seven gemstones. For Shape-norm it is held against the best of its family: a round brilliant, a step cut (a straight-sided outline whose crown facets all face its sides), or a fancy brilliant.
Your stone joins each tool’s list as “your file”, so you can compare it with any of ours. It stays for as long as the browser tab is open, ready in all three tools.
How we checked it
- Every cut in our library, in every format we sell it in (.asc, STL, OBJ, GLB, FBX and STEP, 307 files), opens, and all formats of one cut agree on its shape. The four that curve inward are refused.
- For the 21 cuts in the Brightness & Tilt Analysis, the figures from each file match our own measurement of that cut to within 0.4 points face-up (ISO and table) and 0.6 points of leakage.
- In the simulator, a file of one of our cuts gives that cut’s depth, table, crown height, pavilion depth, girdle, culet and head-on light share, checked on 38 cuts.
- On the wheel, a file of one of our cuts scores within 1 point of that cut on Global, checked on 36 cuts.
- PLY, OFF, 3MF, glTF, .gem and .gcs files written from the T73 give the same stone as its STL, and 51 broken, oversized or hostile files are refused with a message, never a crash.
Your file stays with you
Nothing is uploaded: the file is read in your browser, and no part of it is sent anywhere. It is treated as data only. Nothing in it is run, opened or followed, and the only text shown from it is its file name, cut down to letters, digits and a few marks. The stone is kept for the open tab only. A link you copy or share leaves it out, so whoever opens the link sees one of our cuts instead.
Limits
- A 3D model of a stone with no table, such as a cabochon or a double point, can come in lying on its side. “Turn it over” only fixes upside down; a cutting file always says which way is up.
- A three-sided stone can be laid as the mirror image of how its designer drew it. Its face-up figures are the same; its tilt chart runs the other way.
- The tools’ own sampling moves a few figures slightly with a stone’s size and turn: the table-only figure by about 2 points, and the wheel’s fire by up to about 3. That holds for our cuts too.
- If a file that opens in GemCad, Gem Cut Studio or your CAD program does not open here, send it to support@digitalgemology.com and we will look at why.
Everything else the tools leave out is in What we do not model.