# SurfaceEmitter

SurfaceEmitter generates particles from the surface of an object. New particles are generated by first randomly choosing a face on the tessellated geometry and then a random position on that face. Particles are generated with an initial direction of the normal to that point (including any normal averaging due to normalPerVertex and creaseAngle field settings).

The SurfaceEmitter node belongs to the **ParticleSystems** component and its container field is *emitter.* It is available since X3D version 3.2 or later.

# 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.

### 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).

### SFNode [ ] **surface** NULL [X3DGeometryNode]

The geometry node provides geometry used as the emitting surface.

#### Hint

If the surface is indicated as not being solid (solid field set to false), randomly choose from which side of the surface to emit, negating the normal direction when generating from the back side.

#### Warning

Only valid geometry shall be used.