> ## 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.

# How CAD Becomes Engineering Evidence

> How Forge turns a 3D model into measurements that engineers and reviewers can trace, inspect, and trust.

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

<Note>
  **In plain terms:** A CAD model can show what a ship looks like, but a picture alone
  cannot prove a clearance, volume, or clash result. Forge preserves the chain from the
  original engineering model to the number, the rule, the reviewer, and the final decision.
</Note>

## The difference between a picture and evidence

A 3D viewer is valuable for understanding location and context. It helps a reviewer see
which compartment, component, or opening is being discussed. But the triangles used to
draw a fast picture on a screen are an approximation of the engineering shape.

Forge therefore keeps two related representations:

| Representation           | What it is for                                            | What it is not allowed to do                      |
| ------------------------ | --------------------------------------------------------- | ------------------------------------------------- |
| **Engineering geometry** | Calculating measurements from the imported CAD shape      | It is not silently altered to make a result pass  |
| **Display model**        | Fast viewing, highlighting, annotation, and collaboration | It is not the authority for an engineering number |

The display model helps people see the issue. The engineering geometry supplies the
evidence.

## The evidence chain

<Steps>
  <Step title="1. Preserve the source model">
    Forge records the imported file, its format, its digital fingerprint (a hash that
    distinguishes that exact file version), its units, and how it entered the system.
    For STEP assemblies, it also preserves each component occurrence and its position in
    the assembly.
  </Step>

  <Step title="2. Calculate from engineering geometry">
    A geometry kernel is the software that reads and calculates over the underlying CAD
    shapes. It computes the requested result, such as a volume, a principal dimension,
    or the clearance between two components.
  </Step>

  <Step title="3. Create a measurement record">
    Forge stores the result as a measurement record rather than passing around a loose
    number. The record includes the value, unit, method, source model, import, and exact
    geometry objects involved. This is <Provenance /> applied to geometry.
  </Step>

  <Step title="4. Cite the measurement">
    Any formal claim such as “the clearance is 8 mm” must cite the identifier of that
    measurement record. Forge can then verify that the record exists and belongs to the
    same vessel and model scope.
  </Step>

  <Step title="5. Review and sign the decision">
    The cited claim moves through the verification ladder and responsible human review.
    Once approved, the final decision preserves the evidence chain that supported it.
  </Step>
</Steps>

## Clearance, contact, and clash

These terms sound similar but lead to different engineering actions:

<CardGroup cols={3}>
  <Card title="Clearance" icon="arrows-left-right">
    A positive distance exists between two components. The stored result states the
    distance, unit, measured objects, and source model.
  </Card>

  <Card title="Contact" icon="link">
    The calculated clearance is zero: the components touch. Whether that is intended is
    an engineering question, so the context remains visible.
  </Card>

  <Card title="Clash" icon="triangle-exclamation">
    The components overlap. Forge raises a review flag rather than inventing a negative
    clearance or presenting an uncertain result as settled.
  </Card>
</CardGroup>

## What happens when the model is uncertain

Imported CAD is not automatically authoritative. Units can be missing, scale can be
ambiguous, and some files require repair before they can be read. Repair can also change
the shape.

When that uncertainty could affect a measurement, Forge stops before creating the
measurement record and identifies what needs review. Once the source or import question
is resolved, the calculation can run from a known basis.

This is an important trust behavior: **Forge does not allow the precision of a displayed
number to hide uncertainty in the model that produced it.**

## Why this matters to different reviewers

<CardGroup cols={2}>
  <Card title="Executives and program leaders" icon="chart-line">
    See whether readiness claims are supported by evidence and where review effort is
    concentrated, without needing to inspect the CAD model themselves.
  </Card>

  <Card title="Naval architects and engineers" icon="compass-drafting">
    Move from a flagged issue to the exact components, measurement, model version, and
    governing requirement behind it.
  </Card>

  <Card title="Class and regulatory reviewers" icon="scale-balanced">
    Follow a claim back through its cited measurement and source instead of receiving an
    unexplained number or screenshot.
  </Card>

  <Card title="Yard IT and security teams" icon="shield-halved">
    Keep the source model and its evidence chain inside the approved partner environment,
    with access and processing governed by sensitivity.
  </Card>
</CardGroup>

The next step in the chain is the governed decision itself. See
[How a Decision Gets Made](/concepts/how-a-decision-gets-made).