# Presentation of the geometry building module

## Introduction

The geometry building module of Flux is of boundary type, which means that a volume is described by the bordering faces and a face is described by the bordering lines and a line is described by points.

## Outline of the different steps

The geometry is created in ascending way: first the points, then the lines, and finally the faces and the volumes.

The table below gives a first outline of the description mode of the device geometry.

Step | Description | |
---|---|---|

1 |
Creation of points | Manually by the user |

2 |
Creation of lines | Manually by the user |

3 |
Identification/construction of faces |
Automatically by the software |

4 |
Identification/construction of volumes |
Automatically by the software |

## Creation of points and lines

The points and lines are defined manually (input of point coordinates, selection of the ends of the lines…).

## Construction of faces and volumes (new algorithms)

The faces and the volumes are automatically identified and created (algorithms of automatic construction).

Principle of automatic construction of faces :

- Flux computes all the existing surfaces and it determines to which surfaces belong the points and the lines (A surface contains faces but it is not limited and it is defined by three points linked by two lines).
- The automatic creation of faces is then realized with the aid of a technique of identification of closed outlines.

The principle of the construction of volumes is similar, but more complex, due to the 3D effect.

## Construction of faces and volumes (old algorithms)

In case of difficulties at automatic construction of faces and volumes, the old algorithms of automatic construction are available.

With the old algorithm, each surface is automatically meshed with very loose meshes. By grouping the topological surface elements, the software identifies the faces inside each surface.

The principle of the construction of volumes is similar, but more complex, due to the 3D effect.

## Specificities of the geometry building module

To define the geometry description possibilities offered by the geometry building module, it is necessary to answer to the following questions:

- What are the different authorized shapes of lines and faces?
- How are managed the intersections/superpositions of lines, of lines with faces?
- What are the limits of the algorithms of identification and of automatic construction of faces and volumes?

These different items are treated in the following paragraphs.