## First Level 2D Fundamentals

### Introduction

Learning to use a CAD system is similar to learning a new language. It is necessary to begin with the basic alphabet and learn how to use it correctly and effectively through practice. This will require learning some new concepts and skills as well as learning a different vocabulary. Today, the majority of the Mechanical CAD systems are capable of creating three-dimensional solid models. Nonetheless, all CAD systems create designs using basic geometric entities and many of the constructions used in technical designs are based upon two-dimensional planar geometry. The method and number of operations that are required to accomplish the basic planar constructions are different from one system to another.

In order to become effective and efficient in using a CAD system, we must learn to create geometric entities quickly and accurately. In learning to use a CAD system, lines and circles are the first two, and perhaps the most important two, geometric entities that one should master the skills of creating and modifying. Straight lines and circles are used in almost all technical designs. In examining the different types of planar geometric entities, the importance of lines and circles becomes obvious. Triangles and polygons are planar figures bounded by straight lines. Ellipses and splines can be constructed by connecting arcs with different radii. As one gains some experience in creating lines and circles, similar procedures can be applied to create other geometric entities. In this chapter, the different ways of creating lines and circles in **AutoCAD 2016** are examined.

**AutoCAD Certified User Examination Objectives Coverage **

This table shows the pages on which the objectives of the Certified User Examination are covered in Chapter 1.

Section 1: Controlling the Display in Drawings

Precision

Zoom Extent

Drawing LIMITS

Status Bar

GRID Display

PAN Realtime

Section 2: Creating Basic Drawings

Format

Units Setup

LINE Command

Coordinates

Interactive Input Method

SNAP Option

World Space

User Coordinate System

World Coordinate System

UCS Icon Display

TTR, Circle

Relative Coordinate

Coordinate Systems

Cartesian coordinate system

Absolute Coordinates

Positions, Defining

LINE, Close Option

CIRCLE Command

TTT, Circle

ARC Command

Section 3: Manipulating Objects

ERASE Command

Selection Window

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