# LandXML Import and Export

TunnelCAD reads and writes LandXML files following the LandXML 1.2 specification, with optional TunnelCAD-specific extensions stored in `<Feature>` elements. Version 2.0 files are also supported on import and are auto-detected.

## Exporting LandXML

Open the export dialog from **File > Export LandXML...**.

### Export dialog options

Version
: Select the LandXML version for the output file. Currently LandXML 1.2 variants are available.

Content selection
: Checkboxes control which data categories are written to the file. These are divided into two groups:

**Standard LandXML content** (readable by any compliant application):

- **Alignments** -- horizontal alignment geometry (lines, curves, spirals)
- **Profiles** -- vertical alignment as a sequence of PVI (Point of Vertical Intersection) elements
- **Superelevation** -- cross-slope and cant data along the alignment
- **Cross-section Model** -- design template cross-section lines
- **Cross-section Sections** -- measured cross-section data at each station
- **Survey data (CgPoints)** -- coordinate geometry points from the project

**TunnelCAD extensions** (encoded as `<Feature code="TunnelCAD:...">` elements):

- **Line Definitions** -- section line style assignments and properties
- **Template Line Definitions** -- template line properties
- **Templates** -- full template geometry with bulge arcs
- **Station Definitions** -- template-to-station assignment rules
- **Styles** -- section line styles and alignment styles
- **Volume Definitions** -- per-tunnel volume definitions (color, calculate flag, method, additive constant, four level values + enabled flags, and the term list)

```{note}
TunnelCAD extensions are stored inside standard `<Feature>` elements, so the file remains valid LandXML. Applications that do not recognize the extensions will simply ignore them.
```

Alignment selector
: When the project contains multiple tunnel alignments, choose which ones to include in the export.

File path
: Browse to select the output file location and name.

### Coordinate conventions

LandXML uses a **"Northing Easting"** ordering convention. In TunnelCAD's world coordinate system this maps to **Y X** -- that is, LandXML Northing = World Y and LandXML Easting = World X. The export handles this mapping automatically.

Cross-section points are stored as **offset and elevation** values measured from the alignment axis, not as world coordinates.

## Importing LandXML

Open the import dialog from **File > Import LandXML...**.

### Two-step process

The import follows a scan-then-select workflow:

1. **Select file and scan** -- Browse to a LandXML file and click **Scan**. TunnelCAD reads the file and builds a list of all available data items.

2. **Choose items and import** -- A hierarchical checklist shows the scanned contents organized by category (alignments, profiles, cross-sections, survey points, etc.). Check or uncheck items to control exactly what gets imported, then click **Import**.

### Version detection

TunnelCAD auto-detects the LandXML version (1.2 or 2.0) from the file header. No manual version selection is needed on import.

### Importable data

Standard LandXML elements:

- Alignment geometry (lines, curves, spirals)
- Profile PVIs (vertical alignment)
- Superelevation records
- Cross-section data (template and measured lines)
- Survey points (CgPoints)

TunnelCAD extensions (if present in the file):

- Line definitions and template line definitions
- Template geometry with arc bulge values
- Station definitions
- Section line and alignment styles
- Volume definitions (color, calculate flag, method, additive constant, level values + enabled flags, term list)
- Design review (DR) annotation data

```{tip}
If you are importing a LandXML file that was exported from TunnelCAD, the extension data will be recognized and the round-trip will preserve line definitions, templates, and styles. Files from other applications will import only the standard LandXML elements.
```

### After import

Imported alignments appear in the project tree. Cross-section data is attached to the corresponding alignment stations. You can immediately view imported sections in the Sections canvas tab and alignment geometry in the Alignment canvas tab.

```{warning}
Importing into a project that already contains data will add to the existing content. If you want a clean import, create a new project first via **File > New**.
```