Importing STL Models with Smooth Shading in Three.js

Based on your issue with importing dental STL models from Exocad into Three.js, I can provide some recommendations to help achieve smoother rendering.

Potential Solutions

When STL models appear faceted in Three.js despite looking smooth in the original software, there are several approaches you can try:

1. Export Settings

First, check if your Exocad software offers different STL export options:

• Try exporting with a higher polygon count/resolution
• Look for "smooth" or "high quality" export options
• Some software allows you to specify the level of detail during export

2. STL Loading Process

When loading the STL file, you might want to try using the STLLoader with specific settings:

JAVASCRIPTCopied
import { STLLoader } from 'three/examples/jsm/loaders/STLLoader.js';

const loader = new STLLoader();
loader.load('path/to/your/model.stl', function(geometry) {
  // Process geometry here
  geometry.computeVertexNormals();
  
  const material = new THREE.MeshStandardMaterial({
    color: 0xffffff,
    metalness: 0.1,
    roughness: 0.5,
    flatShading: false
  });
  
  const mesh = new THREE.Mesh(geometry, material);
  scene.add(mesh);
});

3. Geometry Processing

Your current approach includes several good steps, but you might want to try:

JAVASCRIPTCopied
// Remove the mergeVertices step if your model already has proper topology
// geometry = BufferGeometryUtils.mergeVertices(geometry);

// Try a different approach to normal computation
geometry.computeVertexNormals();

// For organic models, you might want to try smoothing the normals
// This is a custom function you would need to implement
// smoothNormals(geometry, Math.PI / 4); // 45 degrees threshold

const material = new THREE.MeshPhongMaterial({
  color: 0xffffff,
  specular: 0x111111,
  shininess: 30,
  flatShading: false
});

4. Consider Alternative Export Formats

If possible, try exporting from Exocad in a different format:

• GLTF/GLB often preserves normals better than STL
• OBJ with MTL can also maintain better surface properties

You could use the appropriate loader:

• GLTFLoader for GLTF/GLB files
• OBJLoader for OBJ files

Additional Considerations

1. STL files typically don't store normal information, so Three.js has to calculate them
2. The mergeVertices() function might be affecting your normals calculation
3. Try experimenting with different material types (MeshStandardMaterial, MeshPhongMaterial)
4. Lighting setup can significantly affect how smooth a model appears

If these approaches don't resolve the issue, you might need to implement a custom normal smoothing algorithm or consider using subdivision surface modifiers to increase the mesh resolution programmatically.