> ## Documentation Index
> Fetch the complete documentation index at: https://www.docs.forgeshipyard.com/llms.txt
> Use this file to discover all available pages before exploring further.

# From Drawings to a 3D Model

> How a stack of legacy 2D sheets becomes a structured, inspectable 3D model without inventing what the drawings do not say.

export const Provenance = () => <Tooltip tip="Knowing where every piece of data came from and what was done to it along the way.">provenance</Tooltip>;

export const Source = () => <Tooltip tip="Anything that comes into the system as input: rules, drawings, datasheets, prior vessel records. Locked once ingested.">source</Tooltip>;

<Note>
  **In plain terms:** Reconstruction is not tracing. It is working out what a set of
  2D sheets actually establishes about a ship, building only that much geometry, and
  recording everything the sheets leave unresolved as a named question instead of
  filling it in.
</Note>

## The problem reconstruction solves

There are two established ways to get a 3D model of a ship, and neither works for
most vessels in service.

* **Scan it.** Laser scanning and LiDAR capture the ship as it is today, but only
  the surfaces a scanner can see. Structure behind a bulkhead, inside a tank, or
  under insulation does not appear. It also requires physical access to the vessel,
  which usually means it is already in dock, which is exactly when you needed the
  model.
* **Use the design model.** This assumes one exists, is complete, is editable, and
  still describes the ship after decades of repair. For an in-service vessel, at
  least one of those is almost always false.

Reconstruction takes the third path: build the model from the record that does
exist. Drawings, survey sheets, and inspection reports describe the whole ship,
including everything a scanner cannot reach, and they exist for vessels that were
never modeled at all.

## What a drawing sheet actually establishes

The central discipline is separating what a sheet **shows** from what a reader
might **assume** from it.

Take a main hatch. A plan sheet may establish the hatch perimeter clearly. That
same sheet says nothing about coaming plate thickness, cover layout, attachment
detail, or present condition. A longitudinal profile sheet may establish the
hatch's envelope in profile without defining its transverse section.

Both facts are real and useful. Neither is a complete description of the hatch.

Forge records that distinction explicitly. Each sheet contributes what it
establishes, scoped to what it establishes, and the reconstruction is built from
the intersection of those contributions rather than from one reader's overall
impression of the drawing set.

## The pipeline

<Steps>
  <Step title="Admit the sources">
    Every drawing sheet, survey record, and report enters as a <Source /> with its
    version, its authority, and where it came from attached. Sources are locked
    once admitted. They are never quietly edited to make a later result work.
  </Step>

  <Step title="Read each sheet for what it establishes">
    Each sheet is interpreted into scoped claims: this perimeter, this station
    spacing, this profile envelope. Every claim stays attached to the sheet and
    region it came from, which is <Provenance /> applied to drawings.
  </Step>

  <Step title="Cross-reference the views">
    Plan, profile, and sectional views have to agree about the same physical thing.
    Where they agree, the reconstruction is well supported. Where they conflict,
    the conflict is recorded as a conflict. It is not averaged away, and neither
    view is silently preferred.
  </Step>

  <Step title="Build only the geometry the evidence supports">
    Geometry is generated for what the sources establish. Where they do not
    establish a shape, no shape is generated. The reconstruction is deliberately
    bounded by its evidence rather than completed for appearance.
  </Step>

  <Step title="Name what is unresolved">
    Every unresolved region becomes a selectable identity carrying its evidence
    envelope and the specific question that would close it: which drawing, survey,
    measurement, or observation is needed. Gaps are inventory, not absence.
  </Step>

  <Step title="Check against type and class precedent">
    Reconstructed components are checked against the vessel's own type and class
    precedent. This is a consistency check that surfaces suspect results, not a
    source of geometry. Precedent can flag that something looks wrong; it is never
    used to invent what the drawings did not say.
  </Step>

  <Step title="Route to human review">
    A reconstruction is a proposal until an accountable person accepts it. Nothing
    becomes approved engineering geometry on import.
  </Step>
</Steps>

## Why gaps stay visible

A reconstruction with no visible holes demonstrates better and is worth much less.

Once invented geometry is in a model file, it is indistinguishable from
evidence-backed geometry. Someone will eventually plan a repair against it, order
steel to it, or hand it to a surveyor. The failure surfaces at the worst possible
moment, and by then nobody can tell which parts of the model were ever real.

So an unresolved region in a Forge model does not disappear and does not get
filled. It stays as a question with a boundary around it. That makes the model
honest in both directions: it tells you what is supported, and it tells you
precisely where it is not.

It also makes collaboration concrete. A named gap is a specific research brief. A
partner with a better drawing, a current survey, or direct observation can close
one and see exactly what it changed.

## Time states stay separate

A ship's record spans decades, and different records describe different moments:
original construction, a later modification, one survey, a different scan years
later.

Forge does not merge these into a single confident model. Each remains a distinct,
labeled evidence state. One configuration serves as the primary assembly, and the
others stay available for comparison. Two records can both be accurate without
describing the same side, surface, date, or physical reference.

This is what makes it possible to ask a question that matters in repair work:
**what changed, and when.**

## From reconstruction to reconciliation

Reconstruction produces a model of the ship as the record describes it.
Reconciliation is the ongoing job of keeping that model true as inspection
findings, repairs, and retrofits change the vessel.

The same discipline carries across. A thickness measurement that disagrees with
the model is recorded as a located conflict, not an overwrite. A completed repair
updates the model through the same review gate as everything else.

<CardGroup cols={2}>
  <Card title="See it on a real vessel" icon="ship" href="/research-cases/balclutha-evidence-workbench">
    A complete 1886 ship reconstructed from its historical drawing set, with all
    of its open questions still visible and selectable.
  </Card>

  <Card title="How geometry becomes evidence" icon="ruler-combined" href="/concepts/how-cad-becomes-engineering-evidence">
    What separates a picture of a measurement from a traceable engineering claim.
  </Card>
</CardGroup>