Course 2 Eng

8/2/2019 Course 2 Eng

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section five.a AutoCAD 3D Object Creation

Three dimensional computer models can be divided into three categories based on the type of primitivesused in the building process: wireframes, surfaces, and solids. Each type has its own creation and editingtechniques.

Wireframe: 2Dobjects drawn in 3D

Surface: faces definethe extents, or surfaceof the model

Solid: objectsrepresent the entiremodels volume

section five.b Wireframe Models

Wireframe modeling consists of lines and arcs connecting points to express form, but does not expresssolid or void. These lines define the boundaries of the form, but require more information than just thedrawing for the form to be understood.

Wireframe models are most often used as aids when constructing models such as for paths when lofting orsweeping objects. You can create wireframe models by positioning 2D (planar) objects anywhere in 3Dspace. AutoCAD also provides some 3D wireframe objects, such as 3D polylines. You can position 2Dobjects in 3D space using several methods:

Create the object by entering 3D points. You enter a coordinate that defines the X, Y, andZ location of the point. Set the default construction plane (XY plane) on which you will draw the object by

defining a UCS. Move the object to its proper orientation in 3D space after you create it.

Following is an example creating a wireframe model for use as a construction aid. In later exercises, wewill build surfaces and solids from the wireframe.

Example Draw a Wireframe Outline of a Column for Construction Referencing

1. Start a new AutoCAD session and draw the columns profile using thePolyline command. Since it will be a round column, you will only need todraw the profile to the center point of the column. It does not matter whatproportions it is, nor where it is drawn relative to 0,0,0.

2. Draw the columns center axis. Use Osnaps to draw a Line orPolylinealong the centerline of the column, from the base to the cap.

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3. Set up multiple viewports to view the column from all sides. Use theVPORTS command to set up 3 viewports: a top view, side view, andisometric.

Save/Restore/Delete/Join/SIngle/?/2//4:

3

Horizontal/Vertical/Above/Below/Left/:

R

After the 3 viewports are laid out, use a combination of the commands UCS,PLAN, and DDVPOINT to change each view.

To create the top view: In the top left viewport, use UCS to change the UCS toWorld, and use PLAN to view the drawing as a floor plan.

To create the side view: In the lower left viewport, use UCS to rotate the UCS 90degrees on the X-axis. Then use PLAN to view the drawing as an elevation.

In the right viewport, use DDVPOINT to create an isometric view.

4. Stand the column upright. In order to use the conventional ROTATEcommand, the UCS must be oriented perpendicular to the objects rotationangle. Use UCS to put it back to World, then rotate the UCS 90 degreeson the X-axis.

After the UCS is oriented perpendicular to an objects rotational center,then it can be rotated using the conventional ROTATE command. Rotatethe column outline and its centerline upright.

5. Save this column wireframe as COLUMN-01 in theC:\ACCUSTUDIO\TUTORIAL directory for use later.

section five.c Surface Models

Surface models, also called meshes, are more sophisticated than wireframe models in that they define notonly the edges of a 3D object but also its extents. Since surface models define the extents of the objectswith meshes, they can have their back-faces hidden. This is a great advantage over wireframe modelsbecause it is easier to view the objects form.

All surfaces are broken down into rectangular or triangular faces, or planes. Because the faces of themesh are planar, the mesh can only approximate curved surfaces. AutoCAD has many different methodsfor creating surface models. Models can be created from primitive objects, constructed from wireframesusing surface tools, or from scratch face by face. Most of the surface commands can be accessed throughthe Surface toolbar:

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There are nine surface primitives: Box, Wedge, Pyramid, Cone, Sphere, Dome, Dish, Torus and Mesh.Most of the primitives can be accessed through the command line by adding the three characters AI_ tothe front of the name, i.e. AI_SPHERE, AI_CONE, AI_BOX, etc. This is cumbersome without writingshortcuts to them, therefore, it is easiest to access the surface primitives from the Surfaces toolbar, or theDraw/Surfaces/3D Surfaces pull-down menu.

Toolbar

Pull-down Draw/Surfaces/3D Surfaces

Keyboard Various (AI_CONE, AI_DISH, etc.)

Another important method of modeling surfaces is through the creation of the surfaces by modifying awireframe model, or creating a meshs faces from scratch. There are six ways of doing this.

Surface Commands3DFACE 3DFACE creates a three- or four-sided surface anywhere in 3D space. You can

specify different Z coordinates for each corner point of a 3D face. The edge(in)visibility can be controlled using I during the command orEDGE after.

REVSURF REVSURF constructs a mesh approximating a surface of revolution by rotatinga path curve, or existing wireframe object, about a selected axis. The revolutionangle can stop before 360 degrees

TABSURF An existing wireframe object controls the path curve, and the extrusion directionfollows an existing vector. No draft angle (taper) is allowed.

EDGESURF This command represents a very limited form of a two-way lofted surface withonly start and end cross-sections. You select four adjoining edges that define thesurface patch, also called a COON patch. The edges can be lines, arcs, splines,or open 2D or 3D polylines, and must touch at their endpoints.

PFACE PFACE is a special type of3DFACE in which individual faces are joined tomake a single multi-faced object. It is typically used by applications rather thanby direct user input.



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3DMESH The location of each vertex in the surface is individually specified in this uniquemethod for making a surface. It is typically used by applications rather than bydirect user input.

THICKNESS Surfaces created by using thickness to extrude them are sometimes called 2-1/2D objects. Although they have three dimensions, the third dimension can

only be a straight side perpendicular to the 2D object at the base. For example, acircle becomes a cylinder and a rectangle becomes an open box.

Surface meshes are tessellated, the curves and shapes are approximated by flat surfaces. Several systemvariables change how surface meshes are created and displayed in the AutoCAD viewports.

Important Surface Modeling System Variables

SURFTAB1andSURFTAB2

You will constantly change these two variables as you build surface models.They control the density of the mesh resulting from commands such asREVSURF, TABSURF, EDGESURF, and RULESURF. SURFTAB1controls the number of surface tabulations in the primary, also called M,

direction. SURFTAB2 controls the other direction, N.

SPLFRAME Controls how edges and control points display. When set to 1, AutoCADdisplays: invisible 3D face edges, only the defining mesh of a surface fitpolygon mesh, control point frame for spline-fit polylines and splines.

SHADEDGE Controls how the SHADE command displays objects. When set to 0, shadefaces with edges not highlighted. When set to 1, shade faces with edges inbackground color. When set to 2, faces not filled, edges in entity color. When setto 3, faces filled with edges in background color.

Example Create a Surface Model from a 2D Wireframe

1. Open the COLUMN-01 drawing (downloadable fromwww.accustudio.com). This is a wireframe drawing of a columns profileand its corresponding centerline axis.

2. Set the two system variables that affect the density of tabulatedsurfaces. Change the SURFTAB1 variable to 3 by typing SURFTAB1 atthe command prompt.

New value for SURFTAB1 : 3

Change the SURFTAB2 variable to a density of5.

New value for SURFTAB1 : 5

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3. Use REVSURF to revolve the columns profile around the centerlineaxis. It is unimportant what the current coordinate system (UCS) is.

Select path curve: Select the columns profile

Select axis of revolution: Select the columns centerline

Start angle : Use the default by typing

Included angle (+=ccw, -=cw) : Use the

default by typing Notice that the amount of surfaces in plan is not enough. Experiment withthe SURFTAB1 variable and repeat step three.

4. Use HIDE to hide the back-faces of the column. Notice that eachviewport is hidden separately.

section five.d Solid Models

Although you can create great-looking models with surfaces, if you want truly realistic or informationallycomplete models, you need to create solids. In real life, all objects have solidity. Even a piece of paper or athin object like fabric has solidity.

Complex solid shapes are easier to construct and edit than wireframes or meshes, however they consumethe most drawing overhead and can increase rendering times when they are curved. This is becauserendering engines break surfaces down the object into triangulated planes in order to perform finite

calculations on each surface.

Similar to surface models, solid models are created by either using primitives or by building off of 2Dwireframe objects. To access most of the solids commands, view the Solids toolbar.

These commands are also available from the pull-down menu Draw/Solids/various options. The easiestway to create 3D solid objects is through basic primitives: BOX, SPHERE, CYLINDER, CONE,WEDGE, and TORUS. You can also create solids by sweeping a 2D object along a path or revolving it

about an axis.

Solid Commands

EXTRUDE Creates unique solid primitives by extruding existing two-dimensional objectsalong a specified path. You can extrude multiple objects with EXTRUDE. Youcan extrude closed polylines, polygons, circles, ellipses, closed splines, donuts,and regions (but not ones that intersect themselves).



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REVOLVE Creates a solid by revolving a two-dimensional object about an axis. The objectsthat can be extruded are the same as forEXTRUDE. You can revolve only oneobject at a time.

SLICE Slices a set of solids with a plane. You can retain both halves of the sliced solidsor just the half you specify. It can be joined back together with UNION. This is

useful for checking the model to be sure it is built correctly.

SECTION Uses the intersection of a plane and solids to create a region. AutoCAD createsregions on the current layer and inserts them at the location of the cross section.This is useful for creating 2D drawings from the 3D model.

INTERFERE Finds the interference of two or more three-dimensional solids and creates acomposite 3D solid from their common volume.

To create more complex solids, you can add, subtract, or intersect them with one another. These are calledBoolean operations. The Boolean operations for solids are accessed from the Modify II toolbar, the

Modify/Boolean/various options, or from the command prompt.

Boolean Operations

UNION Creates a composite region or solid by the addition of multiple solids. Acomposite solid is the result of combining the total volume of two or moreexisting solids. You can join regions or solids that do not share a common areaor volume.

SUBTRACT Creates a composite region or solid by subtraction. This is most commonly usedto create holes, or voids in a solid.

INTERSECT Creates composite solids or regions from the intersection of two or more solidsor regions. It calculates the overlapping area of two or more existing regions andthe common volume of two or more existing solids.

When working with solids, there are many system variables designed to enhance the displaying of them,and also to control how fast the objects display. By knowing these system variables, modeling andrendering is more efficient because you know exactly how the model should be displayed.

Important Solid Modeling System Variables

DELOBJ Determines whether entities used to make solids are deleted. When 1, theoriginal entity is deleted. When 0, the original entity is retained.

DISPSILH Controls the display of curved surfaces on solids in wireframe and hidden object

views. When it is 0, silhouettes of curved surfaces are not shown in wireframeviews. Surfaces are shown as faces in hidden object views. When it is 1,Silhouettes of curved surfaces are shown in wireframe views and hidden objectviews. Surface is not shown as faces.

ISOLINES Sets number of lines on curved surfaces of solids in wireframe views. Valuescan range from 0 to 2047.

FACETRES Controls the size of faces used to display curved surfaces on solids. Values can



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range from 0.01 to 10.00. The larger the value, the smaller the relative size ofthe faces, and the longer it takes to display.

VIEWRES Sets the resolution for object generation in the current viewport. Values canrange from 1 to 20000. This works in conjunction with FACETRES to controlthe tessellation of objects. The higher the number, the more smooth the curves

display, but it also increases rendering and display time. Use this option to gainspeed at the cost of smoothness or to gain visual accuracy at the cost of speed.

Now lets put this information to some use.

Example Create a Hollow Metal Door Frame

1. Open the COLUMN-01 drawing (downloadable fromwww.accustudio.com). This is a wireframe drawing of a columns profileand its corresponding centerline axis. Use this as a base drawing and eraseall of its contents. Save the drawing as a unique name.

2. In the elevation viewport, draw a wireframe outline of a 3 x 7 doorframe using the Polyline command.

Since the door frame will only include the jamb and head profiles, there isnot need to close the polyline across the floor. Note that the UCS has to beoriented correctly in the viewport to draw a 2D wireframe object such as apolyline.

3. In the top viewport, draw the profile of the hollow-metal door jamb.Assume a 4 wide idealized jamb. Since this will be used with theEXTRUDE command later, it will need to be a closed polygon orpolyline.

4. Begin the EXTRUDE command either at the command prompt, on theSolids toolbar, or from the Draw/Solids/Extrude pull-down menu.

Select objects: Select the profile to be extruded

Path/: Use the path option

P

Select path: Select the path drawn in the elevation viewport

5. Use the BOX command to draw a solid door in the frame. It is easiest todraw in the plan and elevation viewports, before moving it (if necessary)in a 3D viewport.

Center/ : Pick a point to begin drawing

one of the doors sides or edges

Cube/Length/: Pick another point to finish drawing



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the side

Height: Define a height for the door, this should probably be done in

another viewport without the ORTHO on.

Once it is drawn, move it with the normal MOVE command, if necessary,

ensuring that the proper coordinate system is utilized.

6. Use another primitive such as a CONE, or SPHERE to cut a hole inthe door for use as a window.

First, create the primitive that will be the cutting tool for the window.

Then, use the conventional MOVE command to move it into position.

7. Cut the primitive out of the door to create a window. Use SUBTRACTto create the void, or opening.

Select solids and regions to subtract from...Select objects: Select the door

Select solids and regions to subtract...

Select objects: Select the window primitive

Notice that under the door assembly, the jamb profile used to extrude along the path is gone. In order toretain objects being extruded, remember to set the DELOBJ system variable to 0 before using theEXTRUDE command.

section five.e Polygon Count

In all types of models, it is important to keep in mind the project scope. Even with ever-faster computersand rendering programs, it is still important to have low-polygon models. There are a number of reasonsto keep the face count down on models, and it is a valued skill. It simply takes longer to display andrender when there are more than necessary faces in the model. There are three things to keep in mind.

An object that remains far away from the camera does not require the same detail as anobject that fills the screen. The distant object can have a lower face count, be less complex,and still be compelling. An object that is not the focus of attention, even though close to the camera, can haveinferred detail. This detail can be created using a texture map rather than creating an overly-complex mesh.

Rendering times are invariably high for complex scenes that have high-resolution models.The lower the face count, the faster the rendering.

TIP



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Because each modeling type uses a different method for constructing 3D models and editing methods varyin their effect on the different model types, it is recommended that you not mix modeling methods withinan object. Limited conversion between model types is available from solids to surfaces and from surfacesto wireframes; however, you cannot convert from wireframes to surfaces or from surfaces to solids.

section five.f AutoCAD 3D Object Editing

Nearly all two-dimensional editing commands work in 3D, such as copy, move, and stretch. There are alsoa number of editing commands that are exclusively for 3D or have special 3D options.

3D Editing Commands

ALIGN Same as for 2D, except use the third source for controlling the 3rd dimension.

ERASE Same as for 2D.

COPY Same as for 2D.

MIRROR Can be used on 3D objects as long as the mirror line is in the XY plane.Otherwise use MIRROR3D and specify the mirroring plane.

OFFSET Can be used in 3D space, but only on 2D objects.

ARRAY Can be used on 3D objects in the XY plane. Otherwise, use 3DARRAY to addlevels in the Z direction.

MOVE Same as for 2D.

ROTATE Can be used on 3D objects in the XY plane. Otherwise, use ROTATE3D torotate objects in any plane.

SCALE Can be used on 3D objects, it always scales in all three dimensions.

STRETCH Can be used in 3D space, but only on 2D objects, wireframes, and surfaces. Theresults may not be what you expect because it is hard to visualize the directionof the stretch unless it is in a plan or elevational view.

LENGTHEN Can be used in 3D space, but only on 2D objects.

TRIM Has special options for 3D but only works on 2D objects such as lines.

EXTEND Has special options for 3D but only works on 2D objects such as lines.

BREAK Can be used in 3D space, but only on 2D objects.

CHAMFER Has special options for 3D to work on solids, not for surfaces.

FILLET Has special options for 3D to work on solids, not for surfaces.

EXPLODE Works on 3D objects solids explode to bodies and regions, polyface meshesbecome faces, polylines with thickness become lines. Faces cannot be explodedfurther.



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TIP Converting Solids into Surfaces

Many times there is a necessity to stretch a solid, or create faceted edges along a curve. However, there is

no direct method for converting solids into surfaces in AutoCAD. If you explode the solid object, it turnsinto Bodies and Regions, which are unusable in rendering. A two-step method for converting solids intosurfaces is through the 3DSOUT and 3DSIN commands, or by using the MESHOUT.LSP found onwww.accustudio.com.

For the 3DSOUT method, use 3DSOUT to export the solid to a 3D Studio file. Since 3D Studio does notdifferentiate between solids and surfaces which have a defined volume, the resulting file is a mesh. Thetessellation, or amount of faces interpreting curves, in the mesh depends on the AutoCAD solid modelingsystem variables discussed in the solid modeling section.

Second, use 3DSIN to import the resulting .3DS file back into AutoCAD. When the dialogue box promptsyou for which information to import, simply select the mesh objects. If you import anything else, the

information will be added to the drawing overhead, such as multiple views with similar names, and defaultrendering settings. Now the mesh is able to be stretched and manipulated because it is a converted to asurface model.

NOTE: certain side effects occur from using this method: AutoCAD cannot use Boolean operations on surfaces The layer names are truncated unless the mesh was on Layer 0 The object is now color byobject, not bylayer

The MESHOUT.LSP follows this same roundabout method, but in one efficient command.

Section six.a Creating a Model From Scratch

Now that you have seen what types of objects, system variables, and editing commands are available, it istime to begin a new drawing from scratch. As you gain experience in modeling, there will be less and lessemphasis on the initial drawing set up. The set up will occur on the fly as each object is created andmanipulated.

In interior design, projects will typically use the similar templates, blocks, and scales. Each modelingproject follows certain steps:

Set up the drawing units, viewports, and system variables Create the walls, floor, and ceiling objects Modify and manipulate the rooms dimensions and fenestration

Insert door, window, and entourage objects Set up the final view

The following five examples build on each other to create a view of a three-dimensional room modelcomplete with furniture and people.

Example six.a.one Set up the Drawing for 3D Modeling

1. Start a new drawing in AutoCAD and set it up for creating a 10x12x9



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high room in 3D. Keep in mind: Units: UNITS Views: VPORTS, VIEW, UCS, ZOOM System Variables: DELOBJ, SURFTAB1, SURFTAB2

Example six.a.two Create the walls, floor, and ceiling objects

1. As objects are created, keep them separated by using separate layers forvarious materials and assemblies.

Begin by drawing the walls in plan on A-WALL. Use SNAPs andPOLYLINEs to draw the edges of the walls so they can be extruded, inother words, ensure that they are closed polylines.

OFFSET the interior polyline of the rooms perimeter to create a wallbase on layer A-WALL-BASE. Copy it to its appropriate 3D layer, and

then use DDCHPROP to give the wall base thickness.

2. Use EXTRUDE to create solid perimeter walls 9 high.

When two rectangular polylines are extruded, they will be two solid boxes.The inner box will need to be subtracted from the outer one to create aroom in the center. To do this, use the Boolean function SUBTRACT.

Ensure that the new solid walls are on the appropriate layer, 3-WALL.

3. In an isometric view, draw 3DFACEs for the ceiling and floor. By usingOSNAPS, create the surfaces as three and four-sided 3DFACES. Keepthem on their appropriate layers, 3-CLNG and 3-FLOR.

The view to the left uses HIDE to show that the ceiling and floor arecorrectly drawn.

4. Save your work to a unique name underC:\ACCUSTUDIO\TUTORIAL .

Example six.a.three Create and manipulate doors and windows1. Use solid primitives to punch holes in the solid walls for a door and awindow. BOXes and Boolean SUBTRACT work well for this.

By creating a BOX to use as a cutting tool, by using SUBTRACT, then itis easier to construct the door that will fill the hole.

Make the door cutting tool 3 wide and 7 tall. Make the window whateversize you wish.



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Notice that the door tool did not cut the wall base. The wall base is asurface mesh, not a solid, so it does not respond to Boolean operations. Inorder to have the wall base wrap around the door opening, it must bemodified with 2D commands such as TRIM, EXPLODE, andSTRETCH or be totally redrawn with new POLYLINE.

2. Now that the voids are created for the door and window, put in the doorand window.

For the door, insert the solid model of the door assembly and all of itsconstruction guides from the solid modeling exercise, DOOR-01. Insertthe block on Layer 0.

For the window, just put a 3DFACE in the middle of the opening torepresent glass. An efficient method for this is to draw a 3DFACE on theinside of the window jamb using the MIDpoint Osnap.

Example six.a.four Insert entourage objects

1. Place entourage in the room from the AutoCAD ADTDesign/DesignPart Library pull-down menu, or insert some from theanywhere that you keep Objects or from the www.accustudio.comexchange section.

Example six.a.five Set up the final perspective views

1. Use DVIEW to set up the final perspective view and save the drawing.


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