Sketch From Image

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 24034f36bad7 · 19 Oct 2026Report an issue or request a re-scan

• Publisherghbalf GitHub userOwner of the repository this skill is read from
• Source folderghbalf/freecad-ai/skills/sketch-from-imageThe exact folder we audited
• LicenceLGPL-2.1As the repository states it
• Commit pinned for this verdict24034f36bad7A new audit runs when the source changes
• Repository statusNot archivedLast push 2 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Extract 2D geometry from an attached image and create a FreeCAD sketch from it.

---
name: sketch-from-image
description: Extract 2D geometry from an attached image and create a FreeCAD sketch from it.
---

# Sketch from Image

Convert an image (drawing, sketch, reference photo, technical drawing) into a
FreeCAD sketch by identifying its geometric shapes and creating a sketch with
equivalent geometry.

## When to use
- User has attached an image and says "create a sketch from this", "trace this
  shape", "make a sketch of this", or similar.
- User wants a starting point for CAD work from a visual reference.

## Required user inputs (ask if missing)

1. **Bounding size in mm** — the real-world size the sketch should occupy.
   Ask as: "What size (in mm) should this sketch be? Provide either the overall
   width or height." Example: "width 40mm" or "height 25mm".
2. **Plane** — default `XY` if not specified. Accept `XY`, `XZ`, `YZ`.
3. **Body name** — if the user wants the sketch on an existing body. Default:
   no body (standalone sketch).

Do NOT guess the size. Without a real dimension, the sketch is useless for CAD.

## Extraction procedure

Look at the attached image (or the textual description if no image is present)
and identify the 2D shapes. For each shape, record:

- **Shape type**: `rect`, `circle`, `polygon`, or `line`
- **Position and size**, scaled so that the overall bounding box matches the
  user-provided dimension (width OR height; preserve aspect ratio)

### Scaling rule

1. Measure the image's apparent bounding box in pixels (or relative units).
2. Compute `scale = user_dimension_mm / measured_dimension_pixels`.
3. Multiply every coordinate and radius by `scale`.
4. **Flip Y-axis if the source uses Y-down** (SVG, screen pixels, most image
   formats). FreeCAD sketches use Y-up. Negate all Y coordinates after scaling.
5. Translate so the sketch is centered around origin (or anchored at 0,0 —
   state which).

### Shape JSON schema (internal — use this shape before calling the tool)

```json
{
  "shapes": [
    {"type": "rect",    "x": 0, "y": 0, "width": 40, "height": 25},
    {"type": "circle",  "cx": 20, "cy": 12.5, "r": 3},
    {"type": "polygon", "points": [[0,0], [10,0], [5,8]]},
    {"type": "line",    "x1": 0, "y1": 0, "x2": 10, "y2": 10}
  ],
  "dimensions": [],
  "notes": "brief description of what was recognized"
}
```

The `dimensions` array is reserved for future use (auto-constraint from
measured values in technical drawings). Leave it `[]` for now.

## Output

After deriving the JSON, call `create_sketch` with the shapes. Do NOT add
constraints — rectangles and circles are auto-constrained. Example:

```
create_sketch(
  plane="XY",
  geometries=[
    {"type": "rectangle", "x": 0, "y": 0, "width": 40, "height": 25},
    {"type": "circle", "cx": 20, "cy": 12.5, "radius": 3}
  ]
)
```

For `line` shapes, emit them as polygons with two points, since `create_sketch`
groups connected line segments into a polygon.

## After creating the sketch

Briefly report:
- Shapes created (count per type)
- Final bounding size
- Any shapes you couldn't confidently identify — list them so the user can
  clarify or re-attach a clearer image.

Do NOT pad, pocket, or otherwise extrude the sketch unless the user explicitly
asks — this skill only produces the 2D profile.

## Iterating on the sketch

If the user wants to adjust the sketch after initial creation, use `edit_sketch`.

**For resizing, moving, or replacing geometry** (most common), use `clear_all=true`
and provide the complete updated geometry:

```
edit_sketch(sketch_name="MySketch", clear_all=true, add_geometries=[
    {"type": "rectangle", "x": 0, "y": 0, "width": 50, "height": 30},
    {"type": "circle", "cx": 6, "cy": 6, "radius": 3}
])
```

This clears all old geometry and constraints, then adds fresh geometry — no
over-constraint issues. The sketch object, plane attachment, and body membership
are preserved.

**For adding new geometry to existing** (e.g. "add a second hole"):
`edit_sketch(sketch_name, add_geometries=[...])`

**For changing dimensions** (e.g. "make it 50mm wide"): use `clear_all=true` with
updated geometry coordinates — dimensions are auto-constrained from the geometry.
Do NOT manually add DistanceX/DistanceY/Radius constraints.

## Limitations (mention if relevant)

- Curves and splines are approximated as polygons; for complex curves the user
  should trace manually or use a dedicated tracing tool.
- Dimension lines and annotations in the image are ignored in v1 (will be
  supported in a future version via the `dimensions` array).
- Hidden lines, section lines, and construction lines are treated as regular
  geometry. If the image uses drafting conventions, warn the user.

Excerpt, first 4,671 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/ghbalf/freecad-ai
git -C freecad-ai checkout 24034f36bad7

Works in

1. 2026-10-19
   ✓SAFE B 89 / 100

   first audit · source 24034f36bad7

Questions about Sketch From Image

• github.com/ghbalf/freecad-ai/tree/master/skills/sketch-from-imag — the audited source at commit 24034f36bad7 and every finding aboveObserved · 19 Oct 2026

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