# Commands

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

## sketch block

A block is a 2D object in a sketch 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: 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.

again, images here would be great

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. All blocks in a set—regular or irregular—must be meshed in order to create zones using the zone generate from-sketch command.

## sketch edge

An edge is 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 lying between the end points that give definition to the edge shape.

## sketch mesh

A number of meshing parameters may be specified in the sketch pane to optimize and fine-tune unstructured meshes. These parameters are global and are used for all the sets present in the program.

## sketch path

A path is a 3D polygon which consists of multiple segments. The path is defined how the mesh is extruded in the third direction.

## sketch point

A point in a sketch 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.

## sketch section

A section is a closed polygon which is determined by at least 3 connected edges.

## sketch segment

The length and blocking of the extruded dimension in a sketch set for FLAC3D are determined by segments. Zoning in the third dimension is defined along segments, similar to the way that zoning is defined along the edges of blocks.

## sketch segment-node

A segment-node is a 3D point which is used to define a segment.

## sketch set

A sketch set comprises blocks that are used to generate zones in FLAC2D or FLAC3D. 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, set deletion, etc.) are performed with set commands.