Solid-Modelling-Internals

The modeller

Geometry Kernel

The Husk

GUI .stl

.sldprt

.sat

Basic Components

• GUI-provides a rendering/viewing facilities. Provides modelling ease

• Husk-Implements operations, controls and manages the parametrization and the solid

• Kernel-maintains the basic geometry. Answers geometric queries posed by the husk.

Post-Modeller Analysis Husks

In this case: Curvature Analysis

GSSL Husks

– AFR/FeatureWorks– CFL/Blend Recognition and Suppression– CollabView– CAMWorks

The Husk-Kernel Interface is very important

The GUI

• Present a Co-ordinate system• Make selection and design of entities easy• Provide interfaces to down-stream analysis and recently• Provide for collaborative design! GUI can make-or-break

The HuskFront Office

• Implements Operations (gets it done from the kernel).

-extrudes/revolves/sweeps -extract parameters and use kernel operations• Maintains design tree and modifications and alerts

user! -maintains the sequence and dependence of the

operations -maintains parameter consistency

The HuskBack Office

• Maintains relationships between geometric entities

-such as between counter-bores/assemblies -across features• Re-sequences operations -roll-back and re-do -record such inter-dependency

Implements operations….

1. Takes the scribe and prepares the Cylinder.

2. Subtracts the cylinder

Maintains and updates design tree…..

Deepen the holeAlert The User!!

Relationships between geometric quantities….

Maintain co-axiality of the two cylinder axes

Counter-Bore Holes

Re-sequences operations

Desired Husk Operation.

Kernel Operation

•Blend the edge first.

•Then do the boss

Kernel

• Maintains the solid as faces/edges/vertices

• Implements operations such as booleans, offsets, and even blends

• Supplies answers to geometric queries

Routine Operations

•Booleans

•blends

A typical Query…

Does the curve C2 on face F intersect the curve C1?

Another query from a CAM husk

• What is the distance between faces S and S’?

CAM picture

S

S’

Can the ball cutter go in?

Kernel Operations

Kernel typical APIs:• Is this point on this face?• Find the closest point to p on surface S• Intersect solids B1 and B2• Compute tangents

The B-Rep of a solid

• Boundary of a solid as a closed surface.

• Inside/Outside and a outward normal

• Surface composed as a collection of faces/edges/vertices

Face

Edge

vertex

Basic Entities

• Face-the 2d-fragment of a surface.

• Edge-the 1d fragment of a curve

• Co-edge-edge as an element of a face

• Vertex-0d element of design space.

• All quantities in design space

• Two-tier representation - combinatorial or

topological - parametric or

geometric

Topology

• Adjacency relationships between face/edge/vertices

• Orientation

All objects here have the same topology.

Topology cont.

• Face-a collection of loops

• Loops-sequence of signed edges

• Edge-ordered pair of vertices

• Vertices-just a Set

Applications of Topology

Husk: check topology! And alert user.

Applications of Topology-IIKernel:Helps in sequencing intersections.

If F intersects F2 boundary along e1, then F1 is next.

Wrap-Up

• The GUI-Husk-Kernel trichotomy• Husk-as the legislative body of operations• Kernel-as the executive body Kernel Representation: Geometry/Topology Topology Details