3D CAD Glossary G - I

Grid
An area on the graphics display covered with regularly spaced dots used as a drawing aid.

Group Technology
(see Part Classification)

Hardcopy
A paper printout or plot of information stored in a computer.

Healing
A series of functions whose purpose is to correct geometric abnormalities contained within a 3D model. Common healing functions may include:

• Surface simplification (mapping spline surfaces to analytic shapes such as planes, cylinders, cones)
• Face stitching
• Edge gap repair

More advanced functions may include:

• The ability to merge coincident vertices
• Repair self-intersections
• Reduce and/or redeploy curve and surface control nodes.

Today's 3D modeling systems typically perform healing on geometry that is imported through neutral data formats such as IGES. These problems can be caused by conditions ranging from:

• Imprecise geometric definitions
• Poor entity mapping
• Poorly written translator code.

Healing may be performed externally (on the neutral file), as it is imported, or internally after the neutral file is imported.

IGES
Acronym for Initial Graphics Exchange Specification. An ANSI neutral graphics file format that describes three-dimensional wire frame and surface model data stored in CAD/CAM systems. Its purpose is to aid in the exchange of geometry, annotation, and structure information between dissimilar systems. See also IPO, ISO and STEP.

Interference
A condition of spatial intersection between two parts in an assembly. Today's 3D modeling applications can not only determine that an intersection exists, but can also display the volume of intersection so that it can be measured and otherwise analyzed.

IPO
Acronym for the IGES/PDES Organization. IPO was created in the late 1970s to develop a neutral file format for the exchange of geometric data among different CAD systems. From this effort IGES was first published in 1980 and has subsequently been adopted as an ANSI standard. IGES Version 5.3 was published in 1996.

A second generation PDE technology, Product Data Exchange Specification (PDES), was initiated during the mid-1980s. Submitted to ISO in 1988, it was adopted as the basis for ISO 10303 (STEP) by the international community. Today, Product Data Exchange using STEP (PDES) is the U.S. project providing U.S. industry inputs to this ISO activity.

ISO (1)
An acronym for International Organization for Standardization. ISO is a worldwide federation of national standards bodies from some 130 countries, one from each country. ISO is a non-governmental organization established in 1947.

The mission of ISO is to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological and economic activity. ISO's work results in international agreements which are published as International Standards.

Iso (2)
An abbreviation for Isometric, a view or drawing of an object where the projections of the x,y, and z axis are spaced 120 degrees apart and the projection of the z axis is vertical.

In many of today's 3D modeling systems, the default view of a 3D part is an isometric view that is slightly skewed. This is because the shaded display of a true isometric view of a 3D part may loose visual detail.

• See also What's Wrong with Isometric Viewing?