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# [Auto]CAD Basics: Foundations and 2D drawings - PowerPoint PPT Presentation

[Auto]CAD Basics: Foundations and 2D drawings. 7E300 International CA(A)D-course www.ds.arch.tue.nl/education/courses/CAD_International/. Overview. Introduction to CA(A)D-Packages: The promise The real world CA(A)D by Example: AutoCAD & ADT History System architecture Basic Geometry

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Presentation Transcript

Foundations and

2D drawings

• Introduction to CA(A)D-Packages:

• The promise

• The real world

• History

• System architecture

• Basic Geometry

• Coordinate systems

• Basic transformations

• Geometric primitives

• Construction aids

• Manual entry

• Snaps

• Alignments

• Construction methods

• Manipulation methods

• Printing

• Getting help

2nd lecture (Friday):

• 3D geometry types

• ‘Intelligent’ composite Objects

• Architectural objects and helpers

• Dimensioning

• Printing

• Rendering

• Export

• Give an overview of the topics involved

• Give introduction to most basic modeling/drawing techniques

• Building is designed assembling different objects

• Every object of the building has a set of properties that can be interpreted in different contexts

• Geometrical representations (i.e. drawings) are only one of many aspects. Drawings can be generated dynamically from existing data

• Different domains (structural engineering, building physics etc.) have different views on building model

• ‘intelligent’ applications can gather all sorts of data (room sizes, material lists etc.) from a well defined model

• Dependent drawings such as sections do not have to be redrawn on changes but automatically adapt

• Problems

• Additional (non-graphical) information has to be provided by architect

• Coherency when changing objects

• Object relations have to be designed

• Complexity with all data required often cannot not be generated at design time

• Architect as ‘building programmer’?

• Virtual/Augmented reality

• Voice recognition

• Reuse of design strategies

• Better compatibility through open standards (IFC etc.)

• Finally: Paperless office at last?

• The promises:

• Let repetitive work be done by the machine

• Draw more exactly

• Draw quicker

• Concentrate on the building instead of the drawing

• Let drawings be generated from a n-dimensional building model

• Get rid of paper by electronic documents

• Accelerate cooperative work in the whole building cycle by reusing documents under domain-specific aspects

• Let ‘intelligent’ functionality take care of easy tasks

• The real world:

• CA(A)D in most cases used as 2D pen and paper

• Additional information required for building model seldom provided by architect

• Document exchange critical due to lack of standards

• Applications not error-prone

• Functionality for architecture domain limited

Marketshare CAAD-packages (Germany 2003) according to online survey on www.aecweb.de

• History:

• 1982 AutoCAD 1.0 introduced on COMDEX

• 1985 AutoCAD 2.1 (R 6) goes 3D

• 1986 AutoLISP

• 1992 R 12 with new Solid kernel & rendering

• 1993 R 12 goes Windows

• 1997 R 14 most important version ever

• 1998 ADT on R 14

• System Architecture (very simplified)

End User

VisualizationOpenGL / D3D

API (C/C++, LISP, VB etc.)

Geometry Kernel

Operating System

• Coordinate Systems

• Almost all CAD-applications based on three-dimensional Cartesian system with right-hand orientation

Image source: http://www.vard.org/mono/gait/soutas.htm

Image source: http://en.wikipedia.org/wiki/Cartesian_coordinate_system

• Coordinate Systems can be modified

• Global: for the entire scene/’world’ (WCS in ACAD)

• Local to an object / arbitrarily chosen by user (UCS in ACAD)

Global (WCS)

Local (UCS)

• Units

• Internal units and precision fixed and limited by machine and application

• Real-world units (m, mm, ft, inches) can be applied arbitrarily suiting own needs

• Be careful when exchanging data!

• Choice of units affects dimensioning, text, hatches and line weights in ACAD!

• Although units can be changed later, conversion problems esp. apply to switch between metric/imperial

• Basic transformations

• Translate (move)

• Rotate

• Scale

• Translation

• Absolute: Set coordinates directly in current coordinate systemExample:Move absolute 5,1(ACAD: move:5,1)

• Translation

• Relative: Set coordinates relative to current location in current coordinate systemExample: Translate relative5,1(ACAD move:@5,1)

• Rotation

• Centered to object

• Rotation

• Off-center rotation

• Scale

• Uniform scaleExample: Factor 0.5 and 2

• Scale

• Non-Uniform scale(Achieved by ‘Stretch’ command in ACAD or by scaling blocks)

• Geometric primitives 2D

• Point (Vertex)

• Elemental type for all other geometry

• Often used as construction aid

• Line

• Elemental type used to assemble other geometry types

• Composed geometry (rectangle etc.) can be broken down to lines

• Conic sections

• Circles, arcs, ellipses, parabolas and hyperbolas are composed of conic sections

• Granularity may be important for printing

Image-source: Mathworld.Wolfram.com

• Circle

• May often be constructed in many different ways:

• Diameter

• 3 Points

• etc

• Arc

• Fraction of circle:

• Can be used to construct complex curvedshapes by composition

• Parametric curves: Bézier spline

• Historically eldest of the free-form curves with some limitations

• Control vertices, control polygon

• Parametric curves: B-spline

• Better control over curve

• Found in many applications

• Parametric curves: NURBS

• Non Uniform Rational B-Spline

• Used by Autocad, most flexible

• X,Y,Z,W coordinates for control points

• Pattern, hatches, fillings

• Can only by applied to closed shapes (‘regions’ in ACAD, sort of 2D solids (more later on))

• Pattern, hatches, fillings (continued)

• Modern applications offer associative fillings

• Copy

• Creates one or more copies of a geometry or groups

• Definition of base point can be used for proper placement

• Array copy

• Multiple copies in rectangular or polar (rotated) series

• Mirror

• Mirror using a mirror axis

• Extend

• Extend lines to arbitrary boundaries

• Trim

• Use arbitrary boundaries to cut away geometry

• Break

• Use two arbitrary boundaries to cut away geometry in-between

• Stretch

• Lengthen/shorten/scale/distort parts of geometries with some parts staying fixed

• Directly enter coordinates into the WCS or current UCS by a comma-separated list with arbitrary precision

• Examples for single points/vertices:1, 2.0, .3relative to last point: @1,2,3.01

• Angular data entry:[Direction] < [Distance]Example: 5 units long line pointing to right in default WCS:90<5.0

• Order of operation in ACAD

• Most command can either be invoked

• Verb – object (state operation first and select objects to apply it to later on)

• Object – verb (Select objects and state which operation to carry out)

• The default method (if no other command explicitly invoked) in ACAD always is set to selection

• Objects can be selected by

• Pick single objects in succession (picking them again de-selects them

• Drag rectangle from up-left to down right to select all objects inside rectangle

• Drag rectangle form down-right to up-left to select those that are either inside or touched by selection rectangle

• ‘Transparent’ operations

• While in the middle of a command sequence, the current command can be suspended for later finish in order to carry out in-between steps

• Most typical examples are the different viewing command (zoom, pan, change perspective etc)

• On the command line transparent mode of a command is activated by putting a ‘ in front of the command statement

• Ortho mode: only rectangular movements of mouse possible

• Snapping: Catch i.e. one of the following points of existing geometry:

• Endpoint

• Midpoint

• Center

• Tangent

• Perpendicular

• Nearest (point on line/curve)

• OSnap tracking:Visual indication of graphic cursor such as

• Parallel to existing line

• Apparent intersection of two lines

• Point on virtual extension of existing line

• Grid: Virtual points in drawing space. When put into exclusive Grid-snap mode only these point can be chosen with the pointing device to construct geometry

• Color / Line weight / Linetype

• Historical method

• Limited to specific set of colors in most applications

• Might interfere with output needs

• Colors not always distinguishable very well

• Blocks / groups

• Complete parts made easily available for reuse

• Manipulate complex parts applying modifications only to on object

• Layers

• Easy metaphor for architects (stacked transparent paper)

• Easy to handle

• Unlimited granularity

• XRefs / inclusions

• Drawing split into smaller entities/files which are composed into a single drawing

• Especially well-suited for group work (different members may simultaneously work on different parts of the building in different files

• Often problematic when moving to other machines / working environments

• DWG

• Proprietary Autodesk format with frequent changes

• Can be im-/exported by many applications

• Features advanced geometry (Solids etc.)

• Can be extended by 3rd party applications

• DXF

• Most established, open standard for data exchange to date, interfaces build into many applications

• Limited set of geometry and information

• Only faces/polygons supported

• No advanced geometry such as solids and NURBS

• IFC

• Developed to suit needs of building industry

• Open

• Extendable

• Lots of advanced meta-data storable

• Not widely supported (yet/anymore)

• Under development / constant change

• XML-version human readable and easy to integrate for collaboration with other applications

• Turn in on 21.03.04 by either creating a webpage and notify me or directly send to (please zip files)[email protected]

• Please document your work progress and hand in questions that will be answered in class on Friday

• If need support also available on ICQ/Yahoo