NURBS Modeling

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AutoCAD Basics Foundations and 2D drawings
7E300 International CA(A)D-course
www.ds.arch.tue.nl/education/courses/CAD_Internat
ional/
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Overview

• Introduction to CA(A)D-Packages
• The promise
• The real world
• CA(A)D by Example AutoCAD ADT
• History
• System architecture
• Basic Geometry
• Coordinate systems
• Basic transformations
• Geometric primitives
• Construction aids
• Manual entry
• Snaps
• Alignments

3
Overview continued

• Construction methods
• Manipulation methods
• Printing
• Getting help

4
Overview continued

• 2nd lecture (Friday)
• 3D geometry types
• Intelligent composite Objects
• Architectural objects and helpers
• Dimensioning
• Printing
• Rendering
• Export

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Goals

• Give an overview of the topics involved
• Give introduction to most basic modeling/drawing
  techniques
• Give advise for self-study
• Give introduction to AutoCAD/ADT

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Building model paradigm

• 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

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Building model paradigm

• Advantages
• 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

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Building model paradigm

• 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

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Future developments

• Architect as building programmer?
• Advanced input techniques
• Virtual/Augmented reality
• Intelligent recognition handmade drawings
• Voice recognition
• Reuse of design strategies
• Better compatibility through open standards (IFC
  etc.)
• Finally Paperless office at last?

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Introduction to CA(A)D packages

• 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

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Introduction to CA(A)D packages

• 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

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CAAD applications in the architectural domain
Marketshare CAAD-packages (Germany 2003)
according to online survey on www.aecweb.de
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CA(A)D by example AutoCAD ADT

• History
• 1960 Ivan Sutherland SKETCHPAD
• 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
• 2000 AutoCAD 2000

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CA(A)D by example AutoCAD ADT

• System Architecture (very simplified)

End User
VisualizationOpenGL / D3D
ADT UI
Standard AutoCAD UI
API (C/C, LISP, VB etc.)
Geometry Kernel
Operating System
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Elemental Computer Graphics

• 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/Cartesi
an_coordinate_system
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Elemental Computer Graphics

• 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)
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Elemental Computer Graphics

• 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

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Elemental Computer Graphics

• Basic transformations
• Translate (move)
• Rotate
• Scale

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Basic geometry

• Translation
• Absolute Set coordinates directly in current
  coordinate systemExampleMove absolute
  5,1(ACAD move5,1)

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Basic geometry

• Translation
• Relative Set coordinates relative to current
  location in current coordinate systemExample
  Translate relative 5,1(ACAD move_at_5,1)

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Basic geometry

• Rotation
• Centered to object

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Basic geometry

• Rotation
• Off-center rotation

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Basic geometry

• Scale
• Uniform scaleExample Factor 0.5 and 2

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Basic geometry

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

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Geometric primitives

• Geometric primitives 2D
• Point (Vertex)
• Elemental type for all other geometry
• Often used as construction aid

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Geometric primitives

• Line
• Elemental type used to assemble other geometry
  types
• Composed geometry (rectangle etc.) can be broken
  down to lines

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Geometric primitives

• Conic sections
• Circles, arcs, ellipses, parabolas and hyperbolas
  are composed of conic sections
• Granularity may be important for printing

Image-source Mathworld.Wolfram.com
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Geometric primitives

• Circle
• May often be constructed in many different ways
• Radius
• Diameter
• 3 Points
• 2 Tangents radius
• etc

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Geometric primitives

• Arc
• Fraction of circle
• Can be used to construct complex curvedshapes by
  composition

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Geometric primitives

• Parametric curves Bézier spline
• Historically eldest of the free-form curves with
  some limitations
• Control vertices, control polygon

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Geometric primitives

• Parametric curves B-spline
• Better control over curve
• Found in many applications

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Geometric primitives

• Parametric curves NURBS
• Non Uniform Rational B-Spline
• Used by Autocad, most flexible
• X,Y,Z,W coordinates for control points

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Geometric primitives

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

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Geometric primitives

• Pattern, hatches, fillings (continued)
• Modern applications offer associative fillings

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Basic operations

• Copy
• Creates one or more copies of a geometry or
  groups
• Definition of base point can be used for proper
  placement

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Basic operations

• Array copy
• Multiple copies in rectangular or polar (rotated)
  series

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Basic operations

• Mirror
• Mirror using a mirror axis

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Basic operations

• Extend
• Extend lines to arbitrary boundaries

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Basic operations

• Trim
• Use arbitrary boundaries to cut away geometry

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Basic operations

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

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Basic operations

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

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Coordinate entry ACAD

• Directly enter coordinates into the WCS or
  current UCS by a comma-separated list with
  arbitrary precision
• Examples for single points/vertices1, 2.0,
  .3relative to last point _at_1,2,3.01

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Coordinate entry ACAD

• Angular data entryDirection lt
  DistanceExample 5 units long line pointing to
  right in default WCS90lt5.0

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Operation and selection

• 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

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Operation and selection

• Selection in ACAD
• 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

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Operation and selection

• 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

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Visual assistance

• 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)

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Visual assistance

• OSnap trackingVisual 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

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Structuring drawings

• 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

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Structuring drawings

• Blocks / groups
• Complete parts made easily available for reuse
• Manipulate complex parts applying modifications
  only to on object

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Structuring drawings

• Layers
• Easy metaphor for architects (stacked transparent
  paper)
• Easy to handle
• Unlimited granularity

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Structuring drawings

• 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

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Standard exchange formats

• 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

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Standard exchange formats

• DXF
• Most established, open standard for data exchange
  to date, interfaces build into many applications
• Human readable ASCII format
• Limited set of geometry and information
• Only faces/polygons supported
• No advanced geometry such as solids and NURBS

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Standard exchange formats

• 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

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Assignment 1

• Turn in on 21.03.04 by either creating a webpage
  and notify me or directly send to (please zip
  files)j.beetz_at_bwk.tue.nl
• 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

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Assignment 1

• Please check
• http//www.ds.arch.tue.nl/education/courses/CAD_in
  ternational/
• Frequently. You will find material, assignments
  and schedule updates here.