### Geometric Modeling

The culture of design & manufacturing incorporates various crucial aspects for the production of a market efficient product. Computer-aided Engineering or CAE comes up as a central part of the entire manufacturing process. Over the years, the function of CAE has evolved so much that it has developed its applications depending upon the type of usage and execution.  Geometric Modeling happens to be one of the most popular CAE applications.

The computer/software generated mathematical representation of an object’s geometry is called Geometric Modeling. As curves are easy to manipulate and bend as per application, geometric modeling uses curves extensively to construct surfaces. The formation of curves can be achieved by,

A set of points,

Analytic functions, or

Other curves/functions

The mathematical representation of an object can be displayed on a computer and used for generation of drawings; which go on for analysis and eventual manufacturing of the object. In general, there are three conventional steps to create a geometric model:

• Creating key geometric elements by using commands like points, lines, and circles.
• Applying Transformations on the geometric elements using commands like rotation, achieve scaling, and other related transformations functions.
• Constructing the geometric model using various commands that integrates the elements of the geometric model to form the desired shape.
##### REPRESENTAION OF GEOMETRIC MODELS
• Two Dimensional or 2D: It projects a two-dimensional view and is used for flat objects.
• 1 2D: It projects the views beyond the 2D and enables viewing of 3D objects that have no sidewall details.
• Three Dimensional or 3D: This representation permits complete three-dimensional viewing of the model with intricate geometry. The most leading process of geometric modeling in 3D is Solid modeling.
##### TYPES OF GEOMETRIC MODELINGS

Depending upon the representations of objects, geometric modeling system can be classified into three categories, which are:

• Solid modeling

Also known as volume modeling, this is the most widely used method as it provides a complete description of solid modeling.

• Wireframe modeling

It is a simple modeling system, which is used to represent the object by the help of lines only. Hence, it is also known as Line model representation. However, wireframe modeling is not enough to express complex solids; therefore, it is used to describe only wiring systems.

• Surface modeling

This type of modeling represents the object by its surface, and it is used to describe the object with a clear view of manufacturing. By this clear point of view, surface modeling cannot be used to develop an internal surface of any model. Surface modeling uses Bezier and B-spines.

Requirements of Geometric Modeling

The various requirements of geometric modeling are as follows:

• The cross-section, hidden lines, dimensions are needed for Graphical Visualization.
• Interchangeable manufacturing tolerance analysis is required while inspection of parts.
• There should also be properties evaluation and geometrical evaluations in Area, Volume, and property evaluation in Weight, Density, etc..
• Need for Finite element analysis and Kinematic analysis.
• Parts classification, planning, etc. in manufacturing.

Geometric modeling is a vast and elaborate field of CAE and requires in-depth study. The next articles dive deep into the various types and facets of geometric modeling.

Every CAD design/model, upon completion, is stored in a respective file format. A 3D file format stores information about 3D models in plain text or binary data. The 3D formats encode a model’s

geometry, which describes its shape,

scene, which includes position of light and peripheral objects;

appearance, which means colors and textures;

and animations, which defines how a 3D model moves.

Not every 3D format stores all such data. Each software comes with its 3D file formats. However, every software has a different file format due to many reasons such as cost, feature, etc. It is necessary for any two software to enable interchangeability/interoperability to make things work. Some of the popular 3D file formats are STL, OBJ, FBX, COLLADA, etc. Each industry comes with its version of 3D file formats. This article gives a brief description of 3D file formats.

##### SALIENT FEATURES OF 3D FILE FORMATS

Considering there are different file types, it is essential to understand the various properties. Different file types allow CAD model viewing in different ways. Some CAD files are limited to only 2D viewing to show the end customer. Following are the main features of 3D file formats:

Proprietary or neutral

The two main types of file format are – proprietary and neutral. All CAD design software uses a proprietary file type. This file type is specific to that particular software. Generally, such file types can only be viewed using the same software it was created with. However, it won’t open in a completely different design program. Proprietary files could be used in intercompany tasks.

Neutral files, on the other hand, are designed to be interoperable. Hence they can be viewed on a multitude of programs. Neutral data come in handy if the document is being distributed to end-users who don’t use CAD software.

Precise or tessellated

CAD designs are displayed in two different ways, namely, precise or tessellated. The difference lies in the fact that the product that is viewed while designing looks quite different from the actual product in real life. It is particularly noticeable in the case of lines and edges that form the product shape. This differentiates between precise drawings versus tessellated drawings.

To create a product, CAD software uses precise lines and angles to complete complex manufacturing processes. Such specific instructions have to be included in a file format to edit the actual drawing or change its design. While displaying a CAD drawing for visual purposes, the lines and edges are tessellated.

Type of assembly

Multi-part designs present a complicated situation while choosing a file format. Depending on the type of file format, multi-part product design may be limited to one single file for the whole assembly. Alternatively, designers also opt for separate files for each component. Awareness of how a particular software will display a multi-part product or if it will display a multi-part product is essential.

Parts Listings

CAD designs accompany models with a list of parts. Different 3D file formats come up with different ways of showing parts list. Two main types of parts list displays are Bill of Material (BOM) and flat list. A bill of material showcases a single part and all its positions in a drawing. A flat list shows all parts individually.

Now that the different features of 3D CAD file formats have been explained, let us walk through some of the popular and most used file formats out there.

##### NEUTRAL FILE FORMATS

To counter interoperability, neutral file formats, also called open source formats, are used as intermediate formats for converting between two proprietary formats. Naturally, these formats are widely used nowadays. Two known examples of neutral formats are STL (with a .STL extension) and COLLADA (with a .DAE extension).  They are used to share models across CAD software.

3D CAD file formats generally fall into two categories: Native or Neutral file formats.

• Native file formats are exclusive to particular CAD software, which can be used with the respective software only.
• Neutral or Standards were explicitly created to enable interoperability, which helps the exchange of files between different CAD software. Neutral file formats allow easier transfer of files with someone who uses different CAD software.
##### DIFFERENT 3D FILE FORMATS
• STEP: STEP is the most recommended and widely used of 3D file Formats. It is an ISO 10303-21 certified standard. Most of the software support STEP importing and exporting.
• IGES: IGES is the abbreviation for Initial Graphics Exchange Specification. It is a vendor-neutral file format. Using IGES, a CAD user can exchange 3D models in the form of circuit diagrams, wireframe, or solid models. Applications backed by IGES include traditional engineering drawings, analysis models, and other manufacturing functions
• Parasolid: Parasolid, initially developed by ShapeData, is now owned by Siemens PLM Software. It is licensed to other companies for use in their 3D computer graphics software products.
• STL: STL, which stands for stereolithography, is the universal format for pure 3D information. It is used in 3D printers and somewhat loved by CAM. STL denotes only the surface geometry of a 3D object without any representation of color, texture, or other common CAD model attributes.
• VRML: VRML stands for Virtual Reality Modeling Language. It is a standard file format for representing 3D interactive vector graphics.
• X3D: X3D is an ISO standard XML-based file format for representing 3D computer graphics. X3D features extensions to VRML (e.g., CAD, Geospatial, NURBS, etc.).
• DXF: DXF stands for Drawing Interchange Format, or Drawing Exchange Format. It is a simple 2D format and technically should be viewed as a Native format. It is Autocad’s native 2D format.