# Commands

Commands on this page: c block, c edge, c mesh, c point, c segment, c set.

## extrude block

A block is a 2D object in an extrusion set consisting of a closed boundary and a mesh within it. Each boundary of a block (external or internal) must contain at least 3 connected edges (where any edge is defined by two end points and a curvature type).

Blocks of two types can be created in the Extruder: regular and irregular. Regular blocks are simply-connected 3- or 4-sided polygons (triangles or quadrilaterals) with structured mesh. All other types of blocks are considered to be irregular and they are meshed with unstructured mesh. Examples of irregular blocks are: blocks containing 5 or more edges on the external boundary (which may be convex or concave), blocks with multiply-connected or multiple boundaries (e.g. a block containing nested blocks), blocks with edges protruding inside.

Both structured and unstructured meshes consist of triangular and/or quadrilateral elements. Upon extrusion, a single zone (brick or wedge) is created from each element of the mesh. An extrusion set must contain valid blocks in order to produce zones when the zone generate from-extruder command is used.

## extrude edge

An edge is principally defined by two end points, and by its curvature type, which must be one of: simple (line), polyline, arc, or spline. Types other than simple will be further defined by control points that lie between the points and give definition to the edge shape.

## extrude mesh

Number of meshing parameters can be specified in the Extruder to optimize and fine-tune unstructured meshes. These parameters are global and used for all the sets present in the Extruder.

## extrude point

A point in an extrusion set is usually an end point (one of two) used to define an edge. They are distinct from control points, which are interior to the points on an edge and are used to shape the line/curve formed by the edge.

## extrude segment

The length and blocking of the extruded dimension in an extrusion set are determined by segments. Zoning in the third dimension is set along segments, similar to the way that zoning is defined along the edges of blocks.

## extrude set

An extrusion set comprises blocks that are used to generate FLAC3D zones. A model may contain multiple sets. At any time, one set is the currently active set in the program. Operations on the set as a whole (block validation, automatic zoning, deletion, etc.) are performed with set commands.