3. BUILDING
THE 3D PART
BUILDING THE 3D PART
3D versus 2D
From profiles
Acting directly on the part
3D constraints
External constraints
RELATING TO THE SKETCH
Assume this profile
Assume fully specified profile of known geometry
Options:
- Extrude
- Revolve
- Sweep along curve
EXTRUDING THE PROFILE
Fully specified! Change
any parameter, it changes the shape
Rule: 3D objects stay connected
to the profile.
Things to consider:
Why don't angles of profiles
show?
Can these angles be changed?
Impact on the solid?
Can we add relationships
later?
MAKING CHANGES
Now make depth=3*height
Is this allowed? Should
I be able to?
How do I show that this
is a driven dimension?
REVOLVING
EXPLICIT SOLID MODELING (THE OLD WAY)
Primitives: cylinder, taper cyl, cuboid, torus, . . . .
Sweep (includes extrude): along line, curve, thru cross sections
(skin)
Revolve: along planar curve, along curve with smooth Z increment
Options - Cap
Operations:
- Booleans: Union, subtract, split, difference
- Edge treatments: Blend,
fillet
- Movement: Copy, move
HISTORY BASED MODELING - DEFINITION
Captures transaction history
Captures the relationships among elements in an order dependent
(sequential) manner
Method for determining the size and orientation of geometric
elements whose interrelationships are defined using an acyclic
directed graph. This method solves for the size and orientation
of geometric elements in a procedural manner.
HISTORY BASED MODELING EXAMPLE
Line B defined as parallel to Line A
HISTORY BASED MODELING ADV/DISADV.
Advantages
- Speed, using sequential recomputation
- Ease of use for initial design
Disadvantage
- Order dependent
- Based on parameters of geometry, or simple equations, to
define the parameters
- Difficult to understand complex inter-relationships and the
build sequence
NON HISTORY BASED MODELING DEFINITION (VARIATIONAL?)
Constraints represented by simultaneous equations
Driving dimensions based on a complex equations
Relationship order independent
Requires known domains
Method for determining geometric elements by simultaneously
solving the set of non-linear equations that declaratively represent
the set of constraints governing the system.
NON HISTORY BASED MODELING ADV/DISADV.
Advantages
- Constraints - order independent
- Under-constrained geometry
- Today's: only in 2D or 2 1/2D
Disadvantages
- Speed
- Requires known problem domain
- Problem complexity severely limits use in 3D
EXTERNAL CONSTRAINTS TO 3D
Would like to tie equational constraints to:
- Spreadsheets
- Solvers (FEA)
- External calculations
- Tables for families of parts
- etc.
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