.AMF File Format – Elements

The file

• UTF-8 XML, starting with the XML declaration and enclosed in one <amf> element. There is no namespace.
• The file may instead be a ZIP archive holding the XML. Both forms keep the extension .amf, and readers tell them apart by content: a ZIP starts with PK (50 4B 03 04), the XML with <?xml. A minimal reader must decompress the file and import at least the geometry, ignoring curvature.
• Elements carry their values as child elements and text, not attributes: a vertex is <coordinates><x>…</x>….
• Numbers use a full stop as decimal separator.

Element tree

amf                     unit, version
├── metadata            type
├── object              id
│   ├── metadata
│   ├── color
│   └── mesh
│       ├── vertices
│       │   └── vertex
│       │       ├── coordinates → x, y, z
│       │       ├── normal      → nx, ny, nz
│       │       ├── color
│       │       └── metadata
│       ├── edge        → v1, v2, dx1 … dz2 (placement unconfirmed)
│       └── volume      materialid, type
│           ├── metadata
│           ├── color
│           └── triangle → v1, v2, v3
│               ├── color
│               └── texmap   rtexid, gtexid, btexid, atexid
├── material            id
│   ├── metadata
│   ├── color
│   └── composite
├── texture             id, width, height, depth, type, tiled
└── constellation       id
    └── instance        objectid → deltax, deltay, deltaz, rx, ry, rz

amf

Children: at least one object; optional material, texture, constellation and metadata elements. Without any material, one default material is assumed.

object, mesh, vertices and vertex

volume and triangle

Volumes of one object may touch and share vertices but must not overlap.

Curved triangles

Triangles are flat unless curvature is given. A normal on a vertex bends every edge meeting there so that the edge is perpendicular to the normal and stays in the plane of the normal and the straight edge. Where the surface has no single normal (a corner, cusp or crease), an edge element gives the tangent directions at the two ends of one edge, and it overrides the normals. The standard requires a curved triangle to be split recursively into four, five levels deep, giving 1024 flat triangles generated while slicing; curvature should not move the surface more than 50% of the triangle’s largest dimension from its plane.

The exact interpolation formulas for curved edges and the subdivision are given in the standard and could not be confirmed from a public source; which element holds the edge elements (the mesh or its vertex list) could not be confirmed either.

color

A colour may sit on a material, object, volume, vertex or triangle. The lowest level wins: triangle over vertex over volume over object over material.

texture and texmap

Early files use map with children u1–u3 and v1–v3; readers accept both. Textures can also be sampled from formulas with tex(textureid, x, y, z).

material and composite

Constant shares make a uniform mixture; formulas make graded materials, lattices and random structures. rand(x, y, z) returns a number from 0 to 1 that stays the same for the same point, and tex() reads a texture. The full list of operators and functions allowed in formulas is in an annex of the standard and is not reproduced in any public source checked.

constellation and instance

Constellations may contain other constellations, without cycles. If a file has several top-level constellations, or several objects outside any constellation, the reader may place them as it likes.

PrusaSlicer adds its own children to instance (scale, scalex–scalez, mirrorx–mirrorz, printable) and to object and amf (layer_config_ranges, custom_code_per_height) with slic3r. metadata types. These are not part of the standard.

metadata

Allowed in amf, object, volume, material and vertex. The type attribute names the item and the text is the value. Reserved types:

Files in the wild also write these names in lower case (name, author).

Worked example

<?xml version="1.0" encoding="utf-8"?>
<amf unit="inch" version="1.1">
  <metadata type="name">Split Pyramid</metadata>
  <object id="1">
    <mesh>
      <vertices>
        <vertex><coordinates><x>0</x><y>0</y><z>0</z></coordinates></vertex>
        <vertex><coordinates><x>1</x><y>0</y><z>0</z></coordinates></vertex>
        <vertex><coordinates><x>0</x><y>1</y><z>0</z></coordinates></vertex>
        <vertex><coordinates><x>1</x><y>1</y><z>0</z></coordinates></vertex>
        <vertex><coordinates><x>0.5</x><y>0.5</y><z>1</z></coordinates></vertex>
      </vertices>
      <volume materialid="2">
        <triangle><v1>2</v1><v2>1</v2><v3>0</v3></triangle>
        <triangle><v1>0</v1><v2>1</v2><v3>4</v3></triangle>
        <triangle><v1>4</v1><v2>1</v2><v3>2</v3></triangle>
        <triangle><v1>0</v1><v2>4</v2><v3>2</v3></triangle>
      </volume>
      <volume materialid="3">
        <triangle><v1>2</v1><v2>3</v2><v3>1</v3></triangle>
        <triangle><v1>1</v1><v2>3</v2><v3>4</v3></triangle>
        <triangle><v1>4</v1><v2>3</v2><v3>2</v3></triangle>
        <triangle><v1>4</v1><v2>2</v2><v3>1</v3></triangle>
      </volume>
    </mesh>
  </object>
  <material id="2">
    <metadata type="name">Hard material</metadata>
    <color><r>0.1</r><g>0.1</g><b>0.1</b></color>
  </material>
  <material id="3">
    <metadata type="name">Soft material</metadata>
    <color><r>0</r><g>0.9</g><b>0.9</b><a>0.5</a></color>
  </material>
</amf>