Doc:Manual/Modelling/Meta Objects

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[edit] Meta Objects

Meta Objects are implicit surfaces, meaning that they are not explicitly defined by vertices (as meshes are) or control points (as surfaces are): they exist procedurally. Meta objects are literally mathematical formulas that are calculated on-the-fly by Blender.

A very distinct visual characteristic of Meta Objects is that they are fluid Mercurial, or Clay-like forms that have a “rounded” shape. Furthermore, when two meta objects get close to one another, they begin to interact with one another. They “blend” or “merge”, as water droplets do (which, by the way, makes them very handy for modeling streams of water when you don't want to do a fluid simulation). If they subsequently move away from one another, they restore their original shape.

There are five predefined Meta Object configurations:

Ball

A point underlying structure.

Tube

A line segment underlying structure.

Plane

A planar underlying structure.

Elipsoid

A spherical underlying structure.

Cube

A volumetric cubic underlying structure.

Each of these is defined by its own underlying mathematical structure, and you can at any time switch between them using the MetaBall tools panel.

Typically Meta Objects are used for special effects or as a basis for modeling. For example, you could use a collection of Meta Objects to form the initial shape of your model and then convert it to another object type for further modeling. Meta objects are also very efficient for ray-tracing.

[edit] Options

Each Meta Object always appears with two rings or circles; see (MetaBall example).

[edit] Pink ring – Selection

The outer ring (labeled “Selection” and coloured pink) is for selecting and exists because there are two types of elements that can be selected within a Meta Object. You can select the Meta Object itself, by clicking the ring, or select the Mesh by clicking the mesh. Without the selection ring you wouldn’t be able to select just the Meta Object.

S with the outer ring selected scales the Meta Object

[edit] Green Ring – Stiffness

The inner ring (labeled “Influence” and coloured green) defines the Meta Object’s stiffness value – how much influence it has on other Meta Objects. See below for more details on this setting.

[edit] 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 neighbouring 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 formulae 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.

[edit] Threshold (Influence)

[edit] Description

Threshold defines how much a MetaObject’s surface “Influences” other MetaObjects. It controls the field level at which the surface is computed. The setting is global to a Group of MetaObjects. As the Threshold increases, the influence that each MetaObject has on one another increases.

[edit] Options

There are two types of influence: positive or negative. The type can be toggled on the MetaBall tools panel using the Negative button. You could think of positive as attraction and negative as repulsion of meshes. A negative MetaObject will push away or repel the meshes of positive MetaObjects.

[edit] “Positive” & “Negative” Influence

A Positive influence is defined as an attraction meaning the meshes will stretch towards each other as the rings of influence intersect. (Positive) shows two MetaBalls’ ring of influence intersecting with a positive influence.

Notice how the meshes have pulled towards one another. The area circled in white shows the green influence rings intersecting.

The opposite effect of a positive influence would be a negative influence: the objects repel each other. (Negative) shows a MetaBall and MetaPlane where the MetaBall is negative and the MetaPlane is positive. Notice how the Negative MetaObject is not visible: only the surrounding circles appear. This is how Blender indicates that the object is Negative.

The white arrow indicates how the sphere is repelling or pushing away the plane’s mesh. This causes the plane’s mesh to “cave in” or collapse inward. If you move the plane away from the sphere, the plane’s mesh will restore itself.

Very interesting screen-savers have been created using animations of positive and negative meta objects together in the same space!

[edit] Wiresize

[edit] Description

The Wiresize controls the resolution of the resultant mesh as generated by the MetaObject.

[edit] Options

Wiresize

The 3D View resolution of the generated mesh. The range is from 0.05 (finest) to 1.0 (coarsest).

Rendersize

The rendered resolution of the generated mesh. The range is from 0.05 (finest) to 1.0 (coarsest).

[edit] Examples

One way to see the underlying mathematical structure is to lower the Wiresize, increase the Threshold and set the Stiffness a fraction above the Threshold.

(Underlying structure) is a (MetaCube) with the above mentioned configuration applied as follows: Wiresize of 0.410, Threshold of 5.0 and Stiffness a fraction above at 5.01.

Underlying structure.

MetaCube.

You can clearly see the underlying Cube structure that gives the MetaCube its shape.

[edit] Stiffness

[edit] Description

Together with Threshold, Stiffness controls the influencing range.

When a Meta Object comes within “range” of another Meta Object the two Meta Objects will begin to interact with each other. They don’t necessarily need to intersect, and depending on the Threshold and Stiffness settings they most likely won’t need to. Stiffness directly controls the green ring surrounding a MetaObject. The field is found on the MetaBall tools panel.

[edit] Options

The range is from 0.0 to 10.0. But to be visible the Stiffness must be slightly larger than the Threshold value. You can visually adjust the Stiffness ring by using the RMB to select it and activating Scale mode with the S.

[edit] Examples

In (Stiffness), the MetaBall labelled “A”, has a smaller Stiffness value than the MetaBall, labelled “B”. As you can see the green ring radius is different between them.

[edit] Grouping

[edit] Description

MetaObjects are grouped by the Family part of an Object name (this is the “OB:” field in most panels, not the “MB:” field).

The Object name is broken into two parts: the left part before, the period, and the right part, after the period. The left part is the “family name”, while the right part is simply a sequential number whose only purpose is to make the object-names unique. For example, the Family part of “MetaPlane.001” is “MetaPlane”. Each meta object in the same “family” is associated with one another as discussed below.

[edit] Options

Groups of MetaObjects are controlled by a base MetaObject which is identified by an Object name without a “number” part. For example, if we have five MetaObjects called “MetaThing”, “MetaThing.001”, “MetaThing.002”, “MetaThing.003” and “MetaThing.004”, the base MetaObject would be “MetaThing”.

The base MetaObject determines the basis, the resolution, and the transformations. It also has the material and texture area. The base MetaObject is effectively the parent of (or perhaps a better word to use is "the owner of") the other MetaObjects in the group.

A group can only have one Material and Texture area. This normalises the coordinates of the vertices. Normally the texture area is identical to the bounding box of all vertices. The user can force a texture area with the T command in Object mode.

[edit] Examples

(MetaBall Base) shows the base MetaObject labelled “B”. The other two MetaObjects are children. Children’s selection rings are always black, while the Group’s mesh is pink. Because the MetaObjects are grouped, they form a unified mesh which can always be selected by selecting the mesh of any MetaObject in the group. For example, in the example (MetaBall Base), only the lower sphere (the parent) has been selected, and you see that both the parent's mesh and all of the children's meshes are now highlighted.

The base MetaObject controls the polygonalization (mesh structure) for the group, and as such, also controls the polygonalization for the children (non-base) MetaObjects. If we transform the base MetaObject, the children’s polygonalization changes. However, if we transform the children, the polygonalization remains unchanged.

[edit] Hints

This discussion of “polygonization” doesn’t mean that the various meshes don’t deform towards or away from each other (Meta objects always influence one another in the usual way, whether or not they are members of the same family). Rather, it means that the underlying mesh structure changes only when the base object transforms. For example, if you Scale the base, the children’s mesh structure changes. In (Scaling the “base”), the base has been scaled down, which has the effect of scaling the mesh structure of each of the children. As you can see, the children’s mesh resolution has increased, while the base decreased. The children did not change size!

[edit] Subpages

1. Editing