Why scans go through PLY to STL
Many scanning and mesh programs save their output as PLY. A PLY can carry more than faces, and a slicer wants only the triangle surface. So a scan usually passes through a PLY to STL step before it reaches the printer.
Picture a scanned replacement knob for a dishwasher: the scan is in hand, and the slicer refuses the file. This page closes that gap in one tab.
What survives the PLY to STL conversion
| PLY data | After conversion |
|---|---|
| Triangle faces | Kept, same count |
| Polygons with more corners | Split into triangles |
| Color per vertex, if stored | Lost; STL describes shape only |
| Points with no faces | Nothing to write; a point cloud has no surface |
| Scale | Numbers copied as stored and shown as millimeters |
For a points-only file, build a mesh from the cloud in your scanning or mesh program first, then come back with the meshed PLY.
Steps for a PLY file to STL
- Drop the .ply here or pick it with Open File.
- The STL is ready when the bar shows
name.stland Download STL. - Open Info: the mesh check lists holes, open edges, non-manifold edges and flipped triangles.
- Use Measure on a feature you know, such as the width of the knob, and compare it with a caliper reading.
- If the size looks wrong, fix it in Edit → Size, run Edit → Repair if needed, and press Download STL.
Typical scan problems and the fixes in this tab
Scans are rarely watertight. The underside the scanner never saw is open, and stray triangles float around the object.
Edit → Repair welds duplicate vertices, removes degenerate and duplicate triangles, turns normals outward and closes simple holes. On an open test box it produced a watertight 8000 mm³ part. Hole filling is a simple fan, good for flat or small gaps and weak on a large curved opening.
Floating fragments show up in Info as extra parts. A flat bottom that the scanner cut off unevenly can be trimmed with Edit → Cut with a plane, which caps the cut and leaves two closed parts; keep the one you need.
Scale, density and file weight
If the scan was saved in meters, a 150 mm vase opens as 0.15 mm. Edit → Size sets the real height in mm and scales the other axes with it.
Scans are dense. A million triangles opens in about 5 to 12 s, and above roughly 1 to 2 million the tab may run out of memory. Edit → Reduce triangles cuts the mesh to a percentage you pick; a test sphere at 30 % kept its volume within 2 %, which is plenty for most printed parts.
Test result, privacy and next steps
A PLY was converted to STL in the test suite and re-opened with the same size, volume and triangle count. Scans of people and rooms stay on your computer: the PLY is read in the tab, and the test run saw zero requests to other domains.
For a full fix pass, open STL repair; for material and print price, the 3D print cost calculator. To inspect the scan before converting, use the PLY viewer. All pairs are on the STL converter page.
Questions and answers
Does the vertex color of my scan survive in the STL?
No. STL has no color field, so the STL is the bare shape. Keep the PLY if you need the colors.
Can I convert a point cloud PLY to STL?
Only if the file has faces. A cloud of points has no surface, so mesh it in your scanning software first.
Why does my scanned model show holes?
Parts the scanner could not see are left open. Run Edit → Repair; it closes simple holes and reports which ones are still open.
Can I convert an STL back to PLY?
Yes. Open the STL, press Convert or Other formats and choose PLY binary.
How large a scan can I convert?
There is no fixed cap. A million triangles opens in about 5 to 12 s; above roughly 1 to 2 million the tab may run out of memory, so reduce the scan in Edit first.
My scan opened as a tiny dot. What happened?
The PLY was probably saved in meters, and the viewer reads the numbers as mm. Set the real length in Edit → Size.
What is the best way to check a scan before printing it?
Open Info after the conversion and read the watertight line first. Then measure one feature you know with Measure, and slice a section with the section plane to look for paper-thin walls that the scanner left behind.