Occlusion and Silhouette Check¶
Test and assessment — instantiates Perspective Depth Projection Design
Verifies that front-to-back order, intersections, and object-identifying silhouettes in the view match the real depth relations of the scene.
Two objects can both be the right size and in the right place and still produce a broken image if the wrong one is drawn in front. Occlusion and Silhouette Check is the assessment that audits who overlaps whom — the front/behind ordering, the intersections and tangencies where forms meet, the hidden edges, and the silhouettes that let a shape be recognized at all. Its defining commitment is depth order and readable outline, not size and not spacing. It asks a different question from any measuring check: not "is this the right length?" but "is this in front of that, and can you still tell what it is?" A figure whose arm reads as growing out of the wall behind it has passed every scale test and failed this one.
Example¶
An animator is composing a crowd shot for a 2D feature: six characters clustered at a market stall, overlapping heavily. The layout artist has placed everyone at the right ground position and scale, but the raw overlaps read as a tangle. The occlusion and silhouette check sorts it out. First, depth order: the vendor is nearest, then the two customers, then the background trio — and every overlap is inspected to confirm nearer figures cleanly cover farther ones, with no character's hand ambiguously threading behind and in front of the same arm. Then intersections: where the vendor's basket meets the stall edge, the contact is checked so the basket sits on the counter rather than floating a hair above or sinking through it. Then silhouettes: each character is tested as a flat black shape against its background, because if two overlapping figures merge into one unreadable blob, the audience loses the staging. One customer's silhouette collapses into the vendor's; the artist nudges a shoulder to reopen the gap. Nothing moved in depth or scale — the fix was entirely about order and outline.
How it works¶
- Compare projected order to reference relations. Sort the scene's entities front-to-back and check each overlap against the true depth relations, so nearer really covers farther.
- Inspect intersections and contacts. Test where forms meet — feet on ground, object on surface, edge through edge — for clean tangency rather than floating or interpenetration.
- Test silhouettes at critical orientations. Read key objects as flat shapes to confirm each stays identifiable and doesn't merge with a neighbor.
- Record intended ambiguity. Distinguish deliberate merging or fragmentation from accidental collapse, and note it so it isn't "corrected" later.
Tuning parameters¶
- Depth-sort granularity — object-level or edge-level sorting. Edge-level catches subtle interpenetrations but is slow; object-level is fast but misses forms that pierce each other.
- Silhouette-test threshold — how much shape separation is required between overlapping forms. Strict separation guarantees readability but can look stiffly spaced; loose allows natural clustering but risks merged blobs.
- Contact tolerance — how much floating or sinking at intersections is accepted. Tight tolerance seats every object firmly but flags harmless near-misses; loose lets objects drift off their contacts.
- Accessibility inclusion — whether safety- and access-critical objects (rails, steps, hazards) are forced into the check even when composition would bury them.
When it helps, and when it misleads¶
The check's strength is that it guards the relations depth-cues and scale tests never touch: a scene can be perfectly measured yet visually impossible if its overlaps cycle or reverse. The problem it polices is the same one computer graphics names the visibility or hidden-surface problem, and its depth-cycle failure is exactly what breaks the painter's algorithm when three surfaces overlap in a loop.[n1]
Its failure mode is treating hidden as absent — an object correctly occluded in the view is quietly deleted from the model, so the next view or the safety review finds it simply gone. A related misuse is an impossible-overlap that reads fine locally, like an Escher joint, passing because no one traced the full cycle. The guarding discipline is to sort against the reference model rather than the eye, keep hidden distinct from deleted, include access and safety objects even when they clutter, and trace overlaps all the way around rather than pair by pair.
How it implements the components¶
occlusion_and_depth_order_map— its core output: the verified front/behind, intersection, and hidden-surface relation among the scene's entities.anchor_and_constraint_set— treats the critical silhouettes and contact points as protected anchors that must stay readable and correctly seated through revision.
It does not measure projected size, ellipses, or foreshortening_and_orientation_model, nor check measuring_and_scale_recession_rule — those belong to Scale and Foreshortening Overlay; this check is about order and outline, never magnitude.
Related¶
- Instantiates: Perspective Depth Projection Design — supplies the depth-order and visibility assessment.
- Consumes: Perspective Grid Construction or a convergence layout supplies the placed scene whose overlaps are sorted.
- Sibling mechanisms: Vanishing-Point Convergence Layout · Perspective Grid Construction · Measuring-Point Interval Transfer · Orthographic or Axonometric View Set · Curvilinear Field Mapping · Atmospheric Depth-Cue Pass · Scale and Foreshortening Overlay · Alternate-View and Section Validation · Viewpoint-Omission Audit
Editorial Notes¶
Form Classification¶
Form family: Assessment, Review & Assurance
Rationale: Occlusion and Silhouette Check operates as a bounded evaluation of existing evidence or work that produces a finding or disposition because it verifies that front-to-back order, intersections, and object-identifying silhouettes in the view match the real depth relations of the scene.
Independent corroboration: The frozen evidence defines Occlusion and Silhouette Check as 'Verifies that front-to-back order, intersections, and object-identifying silhouettes in the view match the real depth relations of the scene', so its operative form is Assessment, Review & Assurance.
Review outcome: Independent reviewer agreement; high confidence.
Origin Attribution¶
Primary origin: Art & Aesthetics
Origin pattern: Convergent development
Present-day reach: Multi-domain
Rationale: Drawing and visual composition independently use overlap and silhouette as primary cues to object identity and spatial depth.
Related originating lineages:
- Cognitive Science — Vision science formalized occlusion and contour as depth and object-recognition cues.
- Computer Science & Software Engineering — Computer graphics developed explicit depth ordering, occlusion tests, visibility algorithms, and silhouette validation for rendered scenes.
- Film & Media Production — Cinematography and animation independently codified readable silhouettes and staging in projected views.
Review resolution: Authoritative-source research resolves the primary-origin disagreement. Silhouette readability and overlap ordering are longstanding visual-composition practices, convergent with the formally specified hidden-surface problem in computer graphics. Origin breadth is limited to formative lineages; present-day applicability is recorded separately as domain_reach=multi_domain.
Encyclopedia synthesis: The exact catalogued form synthesizes established practice rather than reproducing a single standard historical label.
Review outcome: Researched adjudication after independent review; high confidence.
Sources consulted:
Notes¶
[n1] The painter's algorithm resolves visibility by drawing surfaces back-to-front; it fails on cyclically overlapping surfaces (A over B over C over A), the same depth-order impossibility this check hunts for in a scene. ↩