# Adding and deleting sections

## Adding sections

To add sections, click the **Add** button in the **Ribbon > Section** pane. This opens the Add Section dialog, which supports two modes.

### Single mode

Add one section at a specific station. Enter the desired chainage and the section is created at that location.

### Range mode

Create multiple sections at once by specifying:

- **Start station** -- the chainage of the first section
- **End station** -- the chainage of the last section
- **Interval** -- the spacing between consecutive sections

All sections between the start and end stations (inclusive) are created at the given interval.

### Station naming

The Add Section dialog offers two naming conventions:

- **Sequential** -- sections are named with a running counter: Sec 1, Sec 2, Sec 3, and so on.
- **By Station** -- sections are named after their chainage: Sta 0+100, Sta 0+200, etc.

```{tip}
Use "By Station" naming when working with large projects where you need to identify sections by their position along the alignment at a glance.
```

### What happens when a section is added

When a new section is created, TunnelCAD automatically:

1. **Assigns a template** based on the TemplateStationDefs configured for the tunnel. The template that covers the new section's chainage is applied.
2. **Computes the setout offset** from the alignment engine, which determines the section's world-coordinate position, bearing, elevation, grade, and superelevation.

```{note}
The setout offset computation depends on a valid alignment being loaded. If no alignment is defined, sections can still be created but will lack positioning data.
```

## Deleting sections

### Delete current section

Click the **Delete** button in the **Ribbon > Section** pane to delete the currently displayed section.

### Delete range

Click the **Del Range** button in the **Ribbon > Section** pane to open the Delete Range dialog. Specify:

- **Start station** -- the beginning of the range
- **End station** -- the end of the range

All sections whose chainage falls within the specified range are deleted.

```{warning}
Deleting sections cannot be undone. When using Del Range, verify the start and end stations carefully before confirming.
```