geop-ops-reference-geometry

This page is a reference to the crate; how an operation is built is in Lecture 40.

Reference geometry as an operation (see geop-core-editor). AddDatum builds a point, an axis, a plane or a coordinate system from elements picked in the part, in one of the ways CAD systems commonly offer (Construction), and adds it to the part’s datums (see geop-ops-model) under the step’s id:

• points: offset point, midpoint, point on edge, center, projection onto a plane or a line, line meets plane, lines meet, three planes meet;
• axes: through two points, along a line, axis of an arc or cylinder, two planes meet, perpendicular to a plane or a line, parallel through a point, angle bisector, tangent to an edge;
• planes: offset, midplane, through three points, at an angle, through a line and a point, through two lines, parallel through a point, normal to a line or an edge;
• coordinate systems: through three points — at the first, x towards the second, the xy plane through the third.

A coordinate system is used as a point, its origin, and by its axes, like the origin itself: a point offset from it goes along them. Like a sketch’s plane, a datum is built when the step runs, from the part before it, and stays where it was whatever later steps do to what it was built from.

The selection

The step’s selection is a list of Selected (geop_ops_model::selection, a one_of! enum, see geop-core-editor) of anything that can be an input of some construction: a vertex, an edge or a face of the model, a datum, a sketch’s point or curve. What each selected element can be used as — its Shape: a point, a line, a plane, a curve, an arc, something round, a frame — is decided by its shape, not its kind, using geop-core-geometry’s shape recognition: a straight edge is a line and a curve, a circular one a circle, a curve and something round, a flat face a plane. Each construction takes its inputs as Roles, one selected element per input, in any order. Any operation that needs to know “what is this thing” of a polymorphic selection can follow the same pattern.

fitting_constructions says which constructions fit a selection, using exactly the matching a step applies. AddDatum’s dialog is built on it: the selection is a reference field of several elements, which the editor lists with what each can be used as; the constructions are actions, only those that fit enabled, and a construction that stops fitting gives way to the first that does. Offsets are handles and their values numbers or formulas: an offset plane’s distance along its normal, an offset point’s x, y, z along its axes.

Examples

examples (feature examples) offers three parts sketched on datum planes, registered with the operation: boss_on_reference_plane, a boss extruded down from a plane above a box, airfoil_wing, a wing lofted between NACA 2412 sections on planes apart, and conebox, a double cone revolved from a plane turned about a box’s edge, drawn in the editor and kept as the .geop text it saved (src/drawn/). They extrude, revolve and loft, so this crate depends on geop-ops-extrude-revolve.