# Fields

### SFNode [in, out] **metadata** NULL [X3DMetadataObject]

Metadata are not part of the X3D world and not interpreted by the X3D browser, but they can be accessed via the ECMAScript interface.

### SFVec3f [in, out] **position** 0 0 0

Point from which particles emanate.

### SFVec3f [in, out] **direction** 0 1 0

Initial direction from which particles emanate.

### SFFloat [in, out] **speed** [0,∞)

Initial linear speed (default is m/s) imparted to all particles along their direction of movement.

### SFFloat [in, out] **variation** 0.25 [0,∞)

Multiplier for the randomness used to control the range of possible output values. The bigger the value, the more random the output and the bigger the range of possible initial values possible.

#### Hint

Variation of zero does not allow any randomness.

### SFFloat [ ] **mass** [0,∞)

Basic mass of each particle in mass base units (default is grams).

#### Hint

Mass is needed if gravity or other force-related calculations are performed per-particle.

### SFFloat [ ] **surfaceArea** [0,∞)

Particle surface area in area base units (default is meters squared). Surface area is used for calculations such as wind effects per particle.

#### Hints

SurfaceArea value represents average frontal area presented to the wind. Assumes spherical model for each particle (i.e., surface area is the same regardless of direction).