# Computing Feature Mating Poses

> Computes approach, engaged, and mate TCP poses from a held feature in the hand and a fixture feature, resolving free mate symmetries from the current robot pose without executing motion. Use when a held loop must go over a shaft or hook, or a held shaft or tip must enter an aperture, and explicit approach, engaged, and mate poses are needed for planning.

- Skill: `graph-robots/computing-feature-mating-poses` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add graph-robots/computing-feature-mating-poses`
- Raw SKILL.md: https://api.skillmd.com/api/skills/graph-robots/computing-feature-mating-poses/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- License: Apache-2.0
- Author: graph-robots (https://skillmd.com/u/graph-robots)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/graph-robots/computing-feature-mating-poses

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# computing-feature-mating-poses

This skill computes geometry only. When a relation has a free rotational
degree of freedom, it selects the equivalent mate closest to the current TCP
orientation to avoid arbitrary or unreachable reorientation. Its pre-contact
standoff encloses the complete attached-object sphere projection along the
fixture axis, preventing long held bodies from sweeping into the fixture.

## When to use

- A held loop or ring must be placed over a shaft, peg, or hook.
- A held shaft or tip must enter an aperture.
- The mating pose has rotational symmetry that should be resolved from the
  current robot pose.

Use `loop_over_shaft` for a loop or ring placed over a peg or hook. Use
`shaft_into_aperture` for a shaft entering an opening;
`tip_through_aperture` and `insert_through` are accepted aliases. The skill
checks that the relevant inner and outer dimensions have sufficient clearance:
for `loop_over_shaft` the held `radius_inner` against the fixture
`radius_outer`, for apertures the held `radius_outer` against the fixture
`radius_inner`.

For `loop_over_shaft`, describe the fixture at its distal tip with an axis
pointing outward from the mounting surface, `radius_outer`, and the observed
`usable_length` from tip toward the mount. The skill uses these dimensions to
center the shaft inside the loop during crossing, travel to a stable interior
shaft position, and then seat the loop without requiring an object-specific
target point. `crossing_lift_m` (default 0) raises the approach and engaged
poses vertically by that amount after centering, so a long held body that
settles in the hand between observation and crossing still clears the tip;
the mate pose is unaffected. It applies when `usable_length` is declared.

For apertures, the fixture axis points into the opening. The approach is
mirrored onto the free side of the mate, and `insertion_depth` (when the
fixture declares it) moves the engaged and mate poses that far into the
opening.

## Outputs

- `approach_pose` is a collision-free standoff before fixture engagement.
- `engaged_pose` crosses the distal tip far enough for the loop to surround the
  shaft, or enters the aperture.
- `mate_pose` places the loop farther along the usable shaft and seats it, or
  seats the shaft at the requested depth.
- `seating_distance` and `minimum_clearance` describe the computed mate.

## Boundaries

- This skill computes poses but does not plan or execute robot motion.
- Inputs describe functional geometry and a typed relation, not object names.
  Object-specific corrections (a settling offset measured for one tool) enter
  through `crossing_lift_m`, supplied by the graph.
- Execute the result with `planning-held-object-motion` and the corresponding
  motion-execution skills.