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Mesh Formats
- PLY: Arbitrary elements with arbitrary properties. Standard conventions exist. No exact specification.
- STL: Super simple, just a list of faces with face normal and three vertex positions each.
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OFF: ASCII, very simple, only
f32, only position and face-color - OBJ: Fairly powerful, but can't store arbitrary properties. Face, edge and point elements. Extended by MTL format which stores material information.
- COLLADA: By Khronos Group, super extensive, supports nearly everything :P
- FBX: proprietary TODO
- 3DS: proprietary TODO
- X3D: wants to be the standard, but no-one is using it
| ASCII & binary |
|---|
Can store arbitrary elements with arbitrary properties. Since everything is arbitrary, there exist a number of conventions used by most software:
- There exist an element
vertex- It has three
floatordoubleproperties calledx,yandz
- It has three
- There exist an element
face- It has a
vertex_indicesproperty which is a list ofuints. Each list is three entries long.
- It has a
Properties can have the following types:
{u|i}{8|16|32}f{32|64}- Variable length homogeneous lists of one of the primitive types
Each property can be stored as ASCII or as binary in either BE or LE.
ply
format ascii 1.0
element vertex 3
property double x
property double y
property double z
element face 1
property list uchar uint vertex_indices
end_header
0 0 0
1 3 0
2 0 0
3 0 1 2
STL ("specs", wiki, sample files)
| ASCII & binary |
|---|
Very limited. Just a list of triangles each of which specifies a normal and the position of all three vertices. The only type is f32.
solid myname
facet normal ni nj nk
outer loop
vertex v1x v1y v1z
vertex v2x v2y v2z
vertex v3x v3y v3z
endloop
endfacet
endsolid myname
| ASCII only |
|---|
- Only floats
- Vertex data: only 3D pos
- Face data: vertex indices and potentially color (3x
u8)
OFF
# cube.off
# A cube
8 6 12
1.0 0.0 1.4142
0.0 1.0 1.4142
-1.0 0.0 1.4142
0.0 -1.0 1.4142
1.0 0.0 0.0
0.0 1.0 0.0
-1.0 0.0 0.0
0.0 -1.0 0.0
4 0 1 2 3 255 0 0 #red
4 7 4 0 3 0 255 0 #green
4 4 5 1 0 0 0 255 #blue
4 5 6 2 1 0 255 0
4 3 2 6 7 0 0 255
4 6 5 4 7 255 0 0
| basically ASCII only |
|---|
Supports polygonal and free-form objects. To make things easy, we'll completely ignore everything related to free-form objects.
Vertices can have the following properties attached to them:
- position (3d) plus optional weight (only for free form)
- normal (3d)
- UV coordinate (2 or 3 dimensional)
There are point, line and face elements. Faces are specified by specifying the indices of the surrounding vertices in CCW-order. Faces and lines can consist of arbitrarily many vertices.
The format .mtl is closely related to .obj and stores material information. This can probably store arbitrary properties for vertices. Without this however, OBJ files cannot store arbitrary properties. However, OBJ without MTL already stores some rendering information. We should ignore those for now.
v 0.000000 2.000000 0.000000
v 0.000000 0.000000 0.000000
v 2.000000 0.000000 0.000000
v 2.000000 2.000000 0.000000
f 1 2 3
f 3 4 1
| XML |
|---|
Very extensive. Supports arbitrary vertex (and probably face, edge, ...) properties.