# Concepts of propagation and extrusion

## Introduction

To facilitate the geometrical description, various tools for automatic construction are proposed.They allow the duplication of repetitive geometrical patterns, or the fast construction of structures presenting symmetries...

Using the Flux vocabulary we speak about construction by propagation or extrusion. These concepts are clarified below.

## Propagation, extrusion: definition

The basic idea is to automatically generate new objects, based on the objects already created (points, lines, faces) by using transformations ; transformations are geometrical functions of translation, rotation, or affinity type.

At the vocabulary level, we speak about propagation when the created objects (images) are not connected to the basic objects (sources) and about extrusion when these objects are connected among them by connection elements. The connection elements can be of rectilinear or curvilinear type (straight segments or circle arcs).

These concepts are illustrated in the example below.

## Example

In the figure below, the basic face, a rectangle, is propagated/extruded using a transformation of vectorial translation type.

• The propagation automatically generates 2 new rectangles (4 points and 4 lines).
• The rectilinear extrusion automatically generates 2 new rectangles (4 points and 4 lines) as well as 8 connection elements (8 straight lines).