Ashlar-Vellum offers definitions for the following terms in the context of our computer-aided drafting and 3D modeling software.

Associative or Associativity

Pertaining to the association of entities in a model and between features within a model. The function within Cobalt™ and Xenon™ software that automatically updates all related objects when changes are made to the defining geometry, thereby increasing the productivity of design iterations.

Class-A Surface Modeling

Surfaces with optimal aesthetic shape and high surface quality without undesirable waviness or kinks. Internally Curvature-continuous while providing the simplest mathematical representation needed for the shape and smoothness.

Curvature-continuous Surface

The mating of two surfaces having the same position, tangency and curvature along the adjacent edge.

Dynamics or Dynamic Motion or Dynamic Analysis

The calculation of the motion of objects in relationship to forces, torques, inertia and gravity with defined joints, constraints, actuators, springs and dampers.

GD&T or Geometric Dimensioning & Tolerancing

A dimensioning standard sometimes required by the U.S. government and adopted by certain corporations. (ASME Y-1994.5)


3D modeling software without the associative history feature, which can be more time consuming and cumbersome than necessary for simple geometric shapes.

History or History Tree

A list of features and associations of a model in the order created. Found in Xenon and Cobalt, this makes changes to a model fast and easy because features can be selected and edited instead of portions deleted and rebuilt as in Argon. Changes are then rippled through the file and to drawing sheets using Associativity.

Hybrid License

All Ashlar-Vellum CAD and 3D modeling software runs on both Macintosh and Windows platforms, allowing you to switch back and forth between systems as necessary without repurchasing your license.

Kinematics Motion or Kinematic Analysis

The calculation of motion of 3D parts without any reference to the physics involved.

NURBS or NURB Splines

Non-uniform Ration B-Splies are a superset of Bezier curves. These splines are curves created by a complex mathematical formula. For more information see our article What are NURBS and Why are They Important.

NURB Surface

A series of mathematically accurate NURBS control splines where the surface is fitted to the splines. For more information see our article What are NURBS and Why are They Important.

Parametrics, Parametric History, Dimensionally-constrained Parametrics or Equation-driven Parametrics

Pertaining to parameters that define the dimensions of any object. Paramerics in this context can drive the shape of a design by mathematical equations and relationships. When one dimension changes, others within the model will change or not, according to the parameters established to govern those relationships.

A very simple example of a parametric equation: the width of an object can be constrained with parameters to always be 30% of the depth. When the depth is changed, the width changes accordingly.

A very simple example of a relationship: a hole designated as centered on a form will remain in the center no matter how that form changes size and or shape.

Found in Cobalt and Graphite™ only, parametrics are good for part families with varying features. Unlike the parametric tools found in SolidWorks or Pro/Engineer, Cobalt’s parametrics can be used on-demand, so that they don’t constrain creativity.

For more information, see our article What’s Driving Your Model.

Tesselated Data

2D or 3D vector or surface data containing thousands of line segments or triangles. Tessellation is created when a precise geometric shape is broken into a series of small line segments or triangles that will display and print as something that approximates the appearance of the original.