Title: Bridge The Gap — Bridge + Site 3D Model
Domain: engineering — Civil, Architectural & Geospatial Engineering

Summary: Extend an existing 3D site model by adding a bridge designed from the supplied posters, preserving the terrain and surrounding buildings, and export model.obj plus model.3dm.

Task prompt:
You are a BIM modeler using Rhino 8 to add a bridge design to an existing 3D site model.

This is NOT a build-from-scratch task. The site (terrain + surrounding buildings) already exists — you must place the bridge into it and preserve the rest of the site unchanged.

## Inputs
All input materials are under:
  E:\agenthle\engineering\2d_drawings_to_3d_bridge_model\base\input

Required files:
- README.md — natural-language task brief (open this first)
- output_contract.json — machine-readable spec (file names, formats, coordinate convention, required geometry components)
- reference_documents/Posters.pdf — design posters with plans, sections, axonometric of the bridge
- 3D Snapshot.png — rendered preview of the finished site + bridge
- site_model/3D Model_Site.{obj,3dm,dwg} — the EXISTING site you extend

## Software
Open Rhino 8 via:
  E:\agenthle\engineering\2d_drawings_to_3d_bridge_model\base\software\Rhino 8.lnk

## What You Must Do
1. Read README.md and output_contract.json.
2. Open site_model/3D Model_Site.3dm in Rhino. It defines the world coordinate frame — do not move, rotate, or rescale it.
3. Add the bridge: deck, structural supports (piers/abutments), railings/parapet, and a plausible connection to the existing terrain at both ends. Use Posters.pdf for form, deck level, support locations.
4. Export the combined geometry to:
   - E:\agenthle\engineering\2d_drawings_to_3d_bridge_model\base\output\model.obj (Wavefront OBJ ASCII)
   - E:\agenthle\engineering\2d_drawings_to_3d_bridge_model\base\output\model.3dm (Rhino 5.0+ native)
   Both files must contain the original site AND the new bridge geometry.

## Hard Constraints
- Do NOT output any `.dwg` file (evaluator cannot read DWG; forbidden).
- Units = meters. World coordinates inherited from the supplied site model.
- The site geometry in your output must remain visually identical to the input site model — the evaluator scores you on that preservation in addition to bridge correctness.


The agent must:
Read input/README.md and input/output_contract.json to understand the brief, the required filenames, and the coordinate convention.
Open Rhino 8 via the staged software/Rhino 8.lnk shortcut.
Open input/site_model/3D Model_Site.3dm in Rhino to inherit the world coordinate frame and the existing terrain + surrounding buildings.
Add the bridge geometry (deck, piers/abutments, railing/parapet, terrain connection at both ends) from the Posters PDF without moving the existing site.
Export to output/model.obj (Wavefront OBJ ASCII, >=10000 vertices, includes both site and bridge) and output/model.3dm. Do not produce any .dwg output.

Software: Rhino 8

Input files:
name: README.md
format: Markdown
path: input/README.md
description: Natural-language task brief that mirrors the prompt and lists the required bridge components.
name: output_contract.json
format: JSON
path: input/output_contract.json
description: Machine-readable spec — required filenames, magic-byte gates, coordinate convention, units, forbidden patterns, and the list of evaluator view names.
name: 3D Snapshot.png
format: PNG
path: input/3D Snapshot.png
description: Rendered preview of the finished bridge + site — use as a form-check reference.
name: reference_documents/Posters.pdf
format: PDF
path: input/reference_documents/Posters.pdf
description: Design posters with plans, sections, and axonometric of the bridge.
name: site_model/3D Model_Site.obj
format: Wavefront OBJ
path: input/site_model/3D Model_Site.obj
description: Existing site geometry (terrain + surrounding buildings). The OBJ defines the world coordinate frame the bridge must inherit.
name: site_model/3D Model_Site.3dm
format: Rhino 3DM
path: input/site_model/3D Model_Site.3dm
description: Same site model in Rhino native format — open this in Rhino to start the work.
name: site_model/3D Model_Site.dwg
format: DWG
path: input/site_model/3D Model_Site.dwg
description: Same site model in AutoCAD format — provided for reference; the agent does NOT need to output DWG.