shape-analysis

# Shape Analysis — prompt enrichment for 3D parts ## Purpose A short prompt like "phone stand" underspecifies the object: it says nothing about angle, phone size, cable routing, footprint, or style. Modeling it literally yields a bland box. This skill turns a terse description into a **detailed design brief** — the shape, the dimensions, the popular features people actually expect for that object — so the downstream CAD step produces something refined and appealing. This is a **read-only, no-artifact** skill. It writes no files and generates no geometry. Its only output is one enriched design brief, which the user (or the `cadcode` skill) then turns into a model. ## When to use - The user names an object in a few words with no dimensions, features, or style. - The prompt is ambiguous about intended use, target fit (a phone, a bike rail, an M3 bolt), or aesthetic. - The user explicitly asks to "make it nicer / more polished / more popular". Do **not** use it when the user already gave a complete spec, is editing an existing `.py` part, or asked for an exact literal shape ("a 20 mm cube"). ## Workflow 1. **Classify the object.** Map the prompt to a known object category (stand, mount, holder, tray, hook, enclosure, planter, adapter, bracket, …). If the category is unclear, pick the most common reading and state the assumption. 2. **Infer the target it must fit.** Many objects exist to hold or attach to something else. Resolve real reference dimensions: - Consumer devices → typical real sizes (a modern phone ≈ 75 × 160 × 8 mm). - Fasteners / rails / standards → look them up rather than guessing. - When a fit dimension drives the whole part, call it out explicitly and add a printing clearance (0.2–0.4 mm for FDM slip fits). 3. **Add the popular features.** For the category, list the features that make the object genuinely useful and that most well-liked versions include — e.g. a phone stand gets an adjustable viewing angle (~60°), a cable channel, a lip to stop the phone sliding, and a stable weighted base. Prefer features that are printable without supports. 4. **Set concrete dimensions.** Give real numbers, not "medium". Include overall envelope, wall thickness (≥ 2 mm for structural FDM), and any critical internal dimension. Keep the footprint stable (wide base, low center of mass). 5. **Choose a style.** A short aesthetic direction: minimal / geometric / organic / utilitarian. Note fillet radii on handled or visible edges (2–4 mm reads as "finished", sharp reads as "prototype"). 6. **Respect print reality.** Flag overhangs > 45°, thin unsupported spans, and anything needing supports. Prefer a flat, large first-layer face and a single-piece design unless a split obviously helps. 7. **Emit one brief** in the format below and stop. Do not model anything. ## Output format Return exactly one fenced ```design-brief block containing the enriched spec as JSON, followed by a 2–3 sentence plain-language summary. Keep every dimension in millimeters. ```design-brief { "object": "phone stand", "category": "stand", "fits": { "target": "modern smartphone", "ref_mm": [75, 160, 8], "clearance_mm": 0.3 }, "envelope_mm": [90, 80, 70], "wall_mm": 2.4, "features": [ "60° viewing angle", "front lip 8 mm to retain the phone", "rear cable channel 12 mm wide", "wide weighted base for stability" ], "style": "minimal, geometric, 3 mm filleted visible edges", "print": { "orientation": "base flat on bed", "supports": false, "notes": "no overhang > 45°" }, "assumptions": ["single phone, portrait orientation", "PLA on an FDM printer"] } ``` Then: a short summary the user can approve or tweak, e.g. *"A minimal 90×80 mm portrait phone stand at a 60° angle, with a retaining lip, a rear cable channel, and a wide base for stability — printable flat with no supports. Adjust the angle or add a landscape slot if you like."* ## Handoff This skill is standalone: it produces a brief, not a model. When the user wants the object built, hand the enriched brief to the `cadcode` skill as the design input — its concrete dimensions and feature list are exactly what cadcode needs to generate a good `.py` part on the first pass. If the user only asked for analysis, stop after the brief. ## Guidance - Default to **popular, safe, printable** choices; call out every assumption so the user can correct it in one message. - Never invent a precise reference dimension you are unsure of — look it up or mark it as an estimate. - Keep briefs tight. More detail than a modeler can act on is noise; aim for the handful of decisions that most change how the finished object looks and works.