If you've ever worked with 3D scanners or scientific data, you've likely encountered the .PLY extension. While less famous than STL or OBJ, the PLY format is a powerhouse for specific industries.
What is a PLY File?
PLY stands for Polygon File Format (or sometimes the Stanford Triangle Format). It was developed in the mid-90s at Stanford University to store 3D data from 3D scanners.
Unlike STL, which only stores geometry (triangles), PLY is designed to be flexible. It can store:
- Geometry: Vertices and faces (like STL/OBJ).
- Color: Per-vertex color data (unlike STL).
- Normals: Directional data for lighting.
- Confidence: How "sure" the scanner was about a specific point.
ASCII vs. Binary PLY
One of the unique features of PLY is that it comes in two flavors:
ASCII (Text)
Human-readable. You can open it in Notepad and see the list of numbers. Great for debugging but results in massive file sizes.
Binary
Computer-readable only. Compact and fast to load. This is the preferred format for distributing large scans.
When Should You Use PLY?
You should choose PLY over STL or OBJ if:
- You are working with Point Clouds: PLY is excellent for storing raw scan data before it becomes a mesh.
- You need Vertex Colors: If your 3D printer supports full color (like PolyJet) and reads PLY, it's often better than OBJ/MTL because it's a single file.
- Scientific Data: If you need to attach custom data properties to vertices (like temperature or stress values).
However, for standard FDM 3D printing, STL remains the king due to its simplicity and universal slicer support.