# 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.

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