# TIN Terrain

TIN terrain is the preferred terrain input path for v1.

## Purpose

TIN terrain provides existing-ground context for:

- Profile review
- Applied Sections
- Build Corridor
- Earthwork
- future drainage checks

## Workflow

1. Open the TIN command.
2. Load or prepare terrain data.
3. Review the terrain surface.
4. Use it as the accepted existing-ground source for downstream workflows.

## Downstream Use

Applied Sections and Earthwork should read terrain through v1 terrain/TIN contracts instead of relying on ad-hoc viewer geometry.

If Earthwork reports missing existing-ground terrain, confirm that a valid TIN exists and is available to the active project workflow.