# Structure¶

## Technical Details¶

A more formal definition of a meta object can be given as a *directing structure* which can
be seen as the source of a static field. The field can be either positive or negative and
hence the field generated by neighboring directing structures can attract or repel.

The implicit surface is defined as the surface where the 3D field generated by all the directing structures assume a given value. For example a meta ball, whose directing structure is a point, generates an isotropic (i.e. identical in all directions) field around it and the surfaces at constant field value are spheres centered at the directing point.

*Meta* objects are nothing more than mathematical formula that perform logical operations on one another
(AND, OR), and that can be added and subtracted from each other.
This method is also called *Constructive Solid Geometry* (CSG).
Because of its mathematical nature, CSG uses little memory, but requires lots of processing power to compute.

参考

The Wikipedia page about metaballs.

## Underlying Structure¶

Reference

Mode: | Edit Mode |
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Panel: | , |

Blender has five types of metas, each determined by its underlying (or directing) structure.

In Edit Mode, you can change this structure,
either using the relevant buttons in the *Active Element* panel,
or the selector in the *Transform* panel in the Sidebar region.
Depending on the structure, you might have additional parameters,
located in both *Transform* panel and *Active Element* panel.

- Ball (point, zero-dimensional structure)
- This is the simplest meta, without any additional setting. As it is just a point,
it generates an isotropic field, yielding a spherical surface
(this is why it is called
*Meta Ball*or*Ball*in Blender). - Capsule (straight line, uni-dimensional structure)
This is a meta which surface is generated by the field produced by a straight line of a given length. This gives a cylindrical surface, with rounded closed ends. It has one additional parameter:

- Size X
- The length of the line (and hence, of the capsule).

- Plane (rectangular plane, bi-dimensional structure)
This is a meta which surface is generated by the field produced by a rectangular plane. This gives a parallelepipedal surface, with a fixed thickness, and rounded borders. It has two additional parameters:

- Size X/Y
- The length and width of the rectangle.

Note that by default, the plane is a square.

- Ellipsoid (ellipsoidal volume, tri-dimensional structure)
This is a meta which surface is generated by the field produced by an ellipsoidal volume. This gives an ellipsoidal surface. It has three additional parameters:

- Size X/Y/Z
- The length, width and height of the ellipsoid (defaults set to 1.0).

Note that by default, the volume is a sphere, producing a spherical meta, similar to the

*Ball*option...- Cube (parallel-epipedal volume, tri-dimensional structure)
This is a meta which surface is generated by the field produced by a parallelepipedal volume. This gives a parallel-epipedal surface, with rounded edges. As you might have guessed, it has three additional parameters:

- Size X/Y/Z
- The length, width and height of the parallelepiped (defaults set to 1.0).

Note that by default, the volume is a cube.