# Shape Visualization¶

The chunk particles/type_shapes stores information about shapes corresponding to particle types. Shape definitions are stored for each type as a UTF-8 encoded JSON string containing key-value pairs. The class of a shape is defined by the type key. All other keys define properties of that shape. Keys without a default value are required for a valid shape specification.

## Empty (Undefined) Shape¶

An empty dictionary can be used for undefined shapes. A visualization application may choose how to interpret this, e.g. by drawing nothing or drawing spheres.

Example:

{}


## Spheres¶

Type: Sphere

Spheres’ dimensionality (2D circles or 3D spheres) can be inferred from the system box dimensionality.

Key

Description

Type

Size

Default

Units

diameter

Sphere diameter

float

1x1

length

Example:

{
"type": "Sphere",
"diameter": 2.0
}


## Ellipsoids¶

Type: Ellipsoid

The ellipsoid class has principal axes a, b, c corresponding to its radii in the x, y, and z directions.

Key

Description

Type

Size

Default

Units

a

float

1x1

length

b

float

1x1

length

c

float

1x1

length

Example:

{
"type": "Ellipsoid",
"a": 7.0,
"b": 5.0,
"c": 3.0
}


## Polygons¶

Type: Polygon

A simple polygon with its vertices specified in a counterclockwise order. Spheropolygons can be represented using this shape type, through the rounding_radius key.

Key

Description

Type

Size

Default

Units

float

1x1

0.0

length

vertices

Shape vertices

float

Nx2

length

Example:

{
"type": "Polygon",
"vertices": [[-0.5, -0.5], [0.5, -0.5], [0.5, 0.5]]
}


## Convex Polyhedra¶

Type: ConvexPolyhedron

A convex polyhedron with vertices specifying the convex hull of the shape. Spheropolyhedra can be represented using this shape type, through the rounding_radius key.

Key

Description

Type

Size

Default

Units

float

1x1

0.0

length

vertices

Shape vertices

float

Nx3

length

Example:

{
"type": "ConvexPolyhedron",
"vertices": [[0.5, 0.5, 0.5], [0.5, -0.5, -0.5], [-0.5, 0.5, -0.5], [-0.5, -0.5, 0.5]]
}


## General 3D Meshes¶

Type: Mesh

A list of lists of indices are used to specify faces. Faces must contain 3 or more vertex indices. The vertex indices must be zero-based. Faces must be defined with a counterclockwise winding order (to produce an “outward” normal).

Key

Description

Type

Size

Default

Units

vertices

Shape vertices

float

Nx3

length

indices

Vertices indices

uint32

number

Example:

{
"type": "Mesh",
"vertices": [[0.5, 0.5, 0.5], [0.5, -0.5, -0.5], [-0.5, 0.5, -0.5], [-0.5, -0.5, 0.5]],
"indices": [[0, 1, 2], [0, 3, 1], [0, 2, 3], [1, 3, 2]]
}


## Sphere Unions¶

Type: SphereUnion

A collection of spheres, defined by their diameters and centers.

Key

Description

Type

Size

Default

Units

diameters

Sphere diameters

float

Nx1

length

centers

Sphere centers

float

Nx3

length

Example:

{
"type": "SphereUnion",
"centers": [[0, 0, 1.0], [0, 1.0, 0], [1.0, 0, 0]],
"diameters": [0.5, 0.5, 0.5]
}