Tài liệu Mastering Revit Architecture 2008_ Part 7 docx

In this chapter you will learn the basic modeling principles that support the design process in Revit: ◆ The underlying concept of Sketch Based design ◆ How Work Planes, Datums, and Refe

Chapter 6

Modeling Principles in Revit

Creating a BIM model requires modeling in 3D.This is very different from working with abstract 2D lines in order to represent your design To work with Revit and be able to build a BIM model, you need to have an understanding of how objects are constructed at various scales ranging from the building mass down to furniture assemblies You’ll need to know how various building ele-ments interact with each other and depend on each other, what materials they are made of, and how are they constructed and assembled To this end, Revit provides a set of tools that enable you

to build your model and all the elements that go into the model Understanding the principles of modeling in the context of Revit will be essential to your success as you move deeper into building information modeling

In this chapter you will learn the basic modeling principles that support the design process

in Revit:

◆ The underlying concept of Sketch Based design

◆ How Work Planes, Datums, and Reference Planes are used in modeling

◆ Using Revit’s essential form making tools (Extrusion, Sweep, Revolve and Blend)

◆ Combining Solids and Voids to create complex and intriguing forms

Modeling with Revit

Designers have a long tradition of modeling before building This activity involves the use of pliable and tactile materials such as clay and wood to model designs fluidly With these materials, form can be explored with ease, and designs allowed to iterate directly in our own hands The use

of software to model form has become a popular extension of this activity, and you only need to look so far as the latest animated film to see how far the technology has come

There are many software modeling tools that allow direct editing and intuitive shaping of form Tools such as Rhinoceros, 3ds Max, Maya, and SketchUp allow you to create free-form shapes with relative ease These tools are great for modeling, but they are not geared for a BIM approach to design and documents The elements created with these modelers are meshes, nurbs, acis solids, and other generic geometrical shapes that are used to represent walls, slabs, roofs, and windows but they do not have any embedded intelligence or relationships among themselves or with other elements in the model Further, they barely contain any metadata that can be quantified and ana-lyzed So, as it stands today—you will find great modelers that are not BIM and BIM applications that are not powerful modelers One way that Revit approaches this problem is to allow the import

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The entire modeling concept in Revit is based on four base class modeling forms—extrusion, revolution, sweep, and blend—and the combinations that these can produce

Each of the four base modeling techniques can produce either a positive or negative shape that can be combined to create more complex forms Each form is derived from 2D sketches that are drawn on Work Planes We’ll explore in more detail what sketch based forms are in the next section

While there is clearly room for improvements when it comes to the generic modeling ties of Revit, you will be pleasantly surprised with the variety of 3D geometry you can generate in

capabili-a short capabili-amount of time Figure 6.1 shows capabili-an excapabili-ample of whcapabili-at’s possible

Figure 6.1

Example of expressive architecture using Revit

Sketch-Based Design

All internal modeling techniques in Revit rely on an approach called sketch-based design, where you draw a shape in a special sketch mode by creating 2D lines that then generate 3D forms When you start modeling Revit elements, you are basically starting a sketch: Revit enters a mode in which everything but the sketch itself is grayed out so that the focus is given to the sketch, represented in strong magenta colored lines Once you’ve defined the shape by creating closed loops of lines, you click Finish Sketch, and the geometry is generated This sketch mode is used throughout Revit.The Floor and Roof tools both require you to first sketch 2D shapes and then generate the form

by “finishing the sketch.” Revit then applies a thickness based on the element type to the sketch Even walls have an underlying sketch but in the case of the walls this is a sketch that can be edited

in Elevation, not plan view, as shown in Figure 6.2

To edit the elevation of a wall, select the wall in an Elevation or 3D view and click and click the Edit Elevation Profile button in the Options bar Note that this only applies to linear walls

change (Figure 6.3), and you’ll get a set of tools specific to the task of creating 2D sketch lines and creating lines with relationships to other model elements.

Figure 6.2

Moorish architectural example: (A) Standard straight rectangle shaped wall, (B) eleva-tion profile of that wall changed to the desired shape using simple lines, (C) wall shape result achieved

by simple editing of the sketch in elevation ; (D) the wall used in a building

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For example, you can either draw lines freely, or use the Pick Walls tool to generate the floor

or roof sketch lines for you by picking on walls When using the pick walls method, you create an explicit relationship between the sketch and the walls The result is that when walls move, the sketch (and thus the floor or the roof made of it) will adapt and update with the walls

The rules for creating a valid sketch are straightforward:

◆ The line sketch has to form a closed loop of lines, and the lines have to be perfectly trimmed

at edges You cannot have gaps or overlapping lines in the sketch Whenever a sketch is not complete or has overlaps, you will not be able to finish the shape and Revit will indicate that something is wrong with an error message

◆ When creating certain types of elements, you are allowed to sketch more than one shape within the same sketch—this is OK as long as the two sketches do not intersect If the one loop of lines is within the boundaries of the other, that second loop of lines will create a hole

in the shape defined by the bigger one (Figure 6.4)

Figure 6.4

Creating a closed loop within another closed loop of lines results in

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◆ To edit a sketch you need to be in a view that is parallel to the sketch, or a 3D view For example,

it is not logical to edit the sketch of a wall profile in a plan view as you would not be able to see the sketch in a way that is relevant to edit it If you attempt to do this in plan view, Revit will alert you and propose other views in which you CAN execute the task The same goes for a floor—only in plan views or 3D will you be able to edit the sketch

◆ Sketch mode cannot be activated in Perspective (camera) view If you select a wall or any other element and want to edit its shape but cannot find the Edit Shape button in the Options bar, you must be in Camera view Switch to any other view in which the sketch makes sense

A Work Plane can be understood as a surface on which you draw something To understand this better, imagine you are holding a marker in your hand and have a space in front of you—can you draw with the marker in the space? No you need a piece of paper, glass, wall, some kind of a sur-face to draw on So, a Work Plane defines a surface on which you can draw something as a base to build geometry You can define a Work Plane by drawing a Reference Plane, picking a face from an existing element, or use an existing Level (datum) as a reference Let’s look a bit more closely at the types of Work Planes available in Revit:

Reference Planes

These are 2D planes that exist in 3D space They are not visible in 3D views, but can be seen ”edge on“

in other views (plan, section, elevation) and are represented as green dashed lines These lines are not view-specific and will appear in other perpendicular views such as plans, sections and eleva-tions Even though Reference Planes look and feel like ordinary lines, they do not have a ”real“ beginning nor an end They are symbolic representations of infinite planes This means you cannot reference to the beginning or end of a Reference Plane in order to make something like an angular constraint or dimension

Reference Planes are the essence of content creation in the Family Editor as they are used to ate the parametric skeleton to which geometry is then attached They can also affect how other ele-ments relate to the family by giving the Reference Planes various states A Reference Plane can be set as Not A Reference, Weak, or Strong; and it can be defined as a reference for the Left, Right, Front, Bottom, Back, or Center position The selection of these options is important in the Family Editor environment as they define references for snapping Just to give you an idea, when you have two crossing references that are set as Strong, they will define the insertion point of an element when placing it in the Project environment (as shown in Figure 6.6) In Figure 6.6, the two centrally positioned Strong references define the insertion point of the element The Weak references serve

cre-158 CHAPTER 6 MODELING PRINCIPLES IN REVIT

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Reference Lines

These were designed to overcome the limitation of the Reference Planes and their inability to define constraints that reference a point, direction, and angle Unlike with reference Planes, the start and end points of a Reference Line can be referenced and used for dimensioning A popular use of a Reference Line is to define door swing openings by creating an angular relationship between the door leaf position and the closed state of the door leaf Other differences between Reference Lines and Reference Planes are that you cannot name the Reference Lines and you can only select them graphically

Reference Lines define two workplanes—one is the plane on which the Reference Line was drawn, and the other is perpendicular to it (see Figure 6.8)

Figure 6.8

Reference Lines are used to control door swings and opening angle in families

Levels

These are horizontal Datum planes that define the levels in a building and can also be used to denote important horizontal references in a building (attic height, etc.) Levels are only created and visible in Section or Elevation views Each level commonly has a corresponding floor plan view associated with it, although it is possible to make levels with no associated floor plan For example,

a level may define the Top Of Steel in a building section, but there is no need to have a floor plan view of that level For that case, you can create levels without plans by unchecking the option Make Plan View in the Options bar when the level tool is activated This will create a level that appears black and white, rather than blue—indicating that there is no hyperlinked view Note that when you create new levels using the Copy tool, the newly created level an elevation view, the newly cre-ated levels will appear as this black-and white version, as copying levels will not auto-generate new

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When placing elements, they are automatically associated with the Level they are drawn on so that when the level changes position, so will the elements on that level All sketch based families such as floors, roofs, ceilings, and stairs will be associated with at least one level Levels can define both the bottom and top constraints for several elements in Revit, including walls, stairs, and ramps

Grids

These are vertical planes used as standard references in the construction industry for creating tion grids on the site as well as a communication reference between the building participants These construction data are used to accurately define locations for elements such as columns and beams

loca-or position of main structural walls loca-or exteriloca-or shell You can associate elements with the Grids so that when the grid system changes, it controls the position of the associated elements A good example for that would be columns associated with grid intersections As with a level, when a grid is moved, associated elements move with the grid The creation, graphic representation, and control editing

of grids is similar to that of levels (see Figure 6.9)

Figure 6.9

Grids are datum planes that can be used to control other elements such as beams and columns

Once all the Datum planes in Revit have been defined, they will appear in all views that they intersect

So, if you work on a project in a system of grids, you need only draw the grid system once in

a floor plan view, and the grids will be visible in every other plan or ceiling view This may not always be a desired behavior, for example, if your project has a base of 5 floors of shopping with a 30-story hotel above, (like the model shown in Figure 6.8) it’s likely you’ll have separate structural bays for each part of the building You don’t need to see all grid lines of the shopping base in the tower, and vice versa To deal with these scenarios, you can use a Scope Box This will allow you to control in which views a grid will appear

Important note: Grid lines will show in Section or Elevation view ONLY if the view is cut pendicular to the Grid line In no other case will the grid line appear This is done to avoid confusion

per-on cper-onstructiper-on site due to misleading graphic descriptiper-on

Extending Datum Planes

If you wish to expand grids or levels to encompass a larger portion of your model, you can use the text Menu of the grids and select Maximize Extents This will extend the datum planes you haveselected to the maximum extents of the model geometry

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Scope Boxes

These are used when you have multiple floor plans where the gridlines aren’t the same for all levels This tool limits the range in which data elements (grid lines, levels, and reference lines) appear In our example of a building with a base and tower, two separate scope boxes are created for each major volume of the building The grids in each part of the building are then assigned to appropri-ate scope boxes Figure 6.10 shows how scope boxes work in a 3D view

Scope boxes are visible in 3D views (although not in camera views), and you can easily ulate their extent directly using the grip controls Assigning gridlines or other datums to a scope box is easy: Select the gridlines, Select the gridlines and in the Element Properties choose Scope Box and select the scope box where the datums should belong Figure 6.10b shows the Element Proper-ties dialog box for the gridlines and the associated scope box

manip-Figure 6.10

(A) This building consists of two main volumes, low volume with shopping function and a tower with hotel use These two vol-umes use separate grid systems and thus two different Scope Boxes are created to control the visibility

of the separate Grids

(B) Grid element erties indicate the Scope box to which the grid belongs

prop-Work Planes in a Nutshell

Before moving on to look at using work planes in practice, let’s take a moment to summarize the basic theory

A

B

162 CHAPTER 6 MODELING PRINCIPLES IN REVIT

active Work Plane Figure 6.11 graphically explains the Work Plane There are a few simple rules when using or understanding a Work Plane:

◆ Many elements in Revit use the active Work Plane to know where to sketch or place objects (some objects are limited to only horizontal or vertical Work Planes)

◆ The Work Plane is also used when you are modifying objects When you drag or move an object it is typically constrained to be along that plane

◆ When you set the Work Plane to be based on other selectable elements it creates a dency” or relationship to the underlying reference you selected If the underlying object is moved, the Work Plane is moved to stay aligned to it Any objects created on the Work Plane will also update

“depen-Working with Work Planes

When creating elements that are not standard (orientation or geometry) or not automatically nected to a Work Plane, to create them you will need to will need to select the Work Plane tool from the Toolbar This displays the Work Plane dialog shown in Figure 6.12; it’s a good idea to under-stand its options

con-Name This option displays either the available Levels and Grids in the project or the Reference Planes that you have created—if you have named them This is why naming a Reference Plane

is a very important thing

Lines Sketched onActive Work Plane

Model Face

Reference Plane(or other Datum Plane)

Active Work Plane(based on Model Face

or Datum Plane)

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Pick a plane This option allows you to select a plane interactively in the model The selection is graphical/visual and you need to click on a Reference Plane, wall face, faces of other elements—native or linked in the project, any level or grid that you want to become the active Work Plane for the task at hand Figure 6.13 shows the effect of selecting different planes on which to sketch and create a void extrusion.

Figure 6.12

The “Work Plane”

dialog is where you can set the active Work Plane for a view

Figure 6.13

The same mass and the same 2D shape extruded as a hole:

(A) the extrusion shape is drawn on the front face of the mass, (B) the extrusion is drawn on the back face of the mass

Pick a line and use the Work Plane it was sketched in With this option Revit converts the Work Plane on which the line was created into the active Work Plane When you select a Work Plane that is perpendicular to your current view, Revit will open a new Go to View dialog that will give you options to select a view in which the chosen Work Plane can be worked on

(Figure 6.14)

Figure 6.14

The “Go To View”

dialog will list views where you can work on the active Work Plane

164 CHAPTER 6 MODELING PRINCIPLES IN REVIT

Work Plane Visibility

You have the option of displaying the Work Plane visually in your view When visible in 3D, the Work Plane is shown as a semi-transparent grid face (Figure 6.15) By activating the Work Plane Visibility, you’ll see where you will be adding new elements You can see the Work Plane change location by using the Pick Plane option in the Work Plane dialog Select on model faces and you’ll see the active Work Plane change

Figure 6.15

Making the Work Plane visible helps you understand the active Work Plane in

a 3D view

If you are not sure where your active Work Plane is, click the Work Plane Visibility tool in the tool bar:

Other Work Plane Operations

Revit will let you rotate a Work Plane, by clicking on its grid and selecting Rotate from the toolbar This in turn affects how new elements will be placed on that Work Plane You can also use the Work Plane grid to align elements to, and lines will snap to the grid (Figure 6.16)

Figure 6.16

When the Work Plane grid is rotated, new elements placed on the Work Plane will also be “rotated”

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To Change the Work Plane associated with an element, select the element, and then select the

in the dialog

To disassociate an element from a Work Plane, select the element, then select Edit Work Plane

button from the options bar to display the window shown in Figure 6.17 and then select the ciate button The element will then be free to move anywhere in the model Note that this option will only be available for Work Plane based families

Disso-Figure 6.17

The Work Plane dialog allows you to set Work Plane of element, or disassociate it from its Work Plane

Once you have dissociated an element from its Work Plane, you will notice that the value for the Work Plane instance parameter will be set to <not associated> Most importantly, you will notice that the element will be free from constraints and is free to be moved in any three dimensional direction

To Rehost elements from one host (wall, floor, or roof for example) to another, you can use the Rehost button in the Options Bar when an element is selected This allows you to select a new host

to place the element With this tool, you can choose any new host—it does not have to be in same plane as the original For example, you can select a window in one wall, click the Rehost button, then choose a new wall for the window

Figure 6.18 shows an extruded shape originally created on a horizontal Work Plane Using the Rehost tool, the form can be placed on any surface in the model

Figure 6.18

(A) original condition, (B) desired reposition-ing of the curved ele-ment, (C) the element

is rehosted and a tionship between the two elements has been created, (D) the host changed its geometry and the hosted elements follows the change

166 CHAPTER 6 MODELING PRINCIPLES IN REVIT

Using Work Planes with Revit Elements

Below you’ll see two versions of the same building, with roofs that use the same sketch profile but aredrawn on two different Work Planes Image A shows a roof by extrusion sketched on a Work Plane par-allel to the exterior wall; B shows the same roof sketched on a Work Plane rotated 45 degrees withrespect to the exterior wall Notice the difference!

Creating a Roof by Extrusion (Default Work Plane)

Take the following steps to see for yourself how version A was created:

1. Draw four walls in plan view in the shape of a square

2. From the Basic design bar, select the Reference Plane tool and draw a Reference Plane parallel to thesouth wall:

3. Pick the Reference Plane and go to element properties Give it a Name, “Front Roof Plane”

4. From the Modeling design tab, Select the Roof tool and select Roof By Extrusion

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5. You will be prompted to select a Work Plane:

From the Name list, select the named Reference Plane you just drew You’ll be asked to open a view tobegin sketching Choose the South Elevation

6. Sketch a roof in arc shape as shown here and finish the sketch

7. Go to the default 3D view and using the blue arrows, adjust the length of the roof to make sure itextends beyond the exterior walls as shown here

168 CHAPTER 6 MODELING PRINCIPLES IN REVIT

8. While still in the 3D view, select all the walls Click the Attach button in the Options bar and thenselect the roof to attach the walls to the roof The resulting roof should look something like this:

9. To make the roof end at the edge of the exterior walls, select the roof in plan view and select theoption Cut Plan Profile in the Option bar This allows you to cut off the extruded roof exactly at theedge of the building, regardless of its shape In this example, draw two rectangles that cut the roof

up to the face of the walls

Wall

Roof Cut Plan Profile

Cut Plan Profile

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After using Cut Plan Profile, the final result for the first roof looks like this:

Creating a Roof using a 45 degree oriented Work Plane as a reference

To obtain the second roof (B), repeat all previous steps, but draw the Reference Plane at a 45 degree angle

to the building as show below Remember to give the Reference Plane a different name in the ElementProperties dialog

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Principles of Modeling in Revit

Revit is much more than a 3D modeler It is built specifically for architects and has behavioral rules built into many of the architectural elements that make up the building For example, walls usually are vertically extruded rectangular shapes; floors and ceilings are horizontal extruded shapes with constant thickness These major building elements (System Families) use a restricted sketch-based approach because those restrictions make sense for these types of elements This is one of Revit’s major differences compared with a generic modeler where you can model anything, any way you like In Revit, the type of element you are modeling will present a more tailored set of creation tools You draw a wall by defining its start and end point, which will determine its position and length The width of the wall and its height are determined by the wall properties The wall becomes 3D immediately with each click of the mouse Roofs and Floors, on the other hand, require

a definition of a sketch that determines their outer shape while their thickness is what is defined in the Element properties of the Roof or the Floor

Once the envelope of the building has been established with walls, floors, and roofs (the system families) you progressively add windows, doors, furniture, plumbing fixtures, and so on (standard fam-ilies) to the model These elements rarely depend on the context of the building and are usually built off site and manufactured in some factory in real life In Revit, a good selection of these elements

is pre-prepared and saved in a library for use across multiple projects These loadable elements are all created in the Family Editor using a combination of simple geometric forms that can be associ-ated with parametrically driven dimensions For example, a chair can be created with a combina-tion of sweeps, blends, extrusions, and revolves The same applies to a lighting fixture, a sitting bench, a plumbing fixture—you name it Figure 6.19 shows samples of standard “loadable” family types

The finished roof looks like this:

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Figure 6.19

These windows and doors belong to the standard “loadable”

family types

In some cases, you need the full flexibility of the Family Editor in the context of your project When you need to create a custom design feature tightly related to the context of the building or the landscape around it (entrance canopy, reception desk in welcome area, etc.) you’ll need a robust set

of tools that are not available using the basic walls, floors and roofs These types of elements are ated using the Create tool from the Modeling tab in the Design bar (Figure 6.20) and they use the same features available in the family editor, and are referred to as “in-place families.” Figure 6.21 shows

cre-a fireplcre-ace built cre-as cre-an “In-Plcre-ace” Fcre-amily

Figure 6.20

The Modeling design bar

172 CHAPTER 6 MODELING PRINCIPLES IN REVIT

Figure 6.21

Example of an In Place family

Another workflow where free-form modeling comes into play is at the early stages of conceptual design, where massing studies are explored These mass forms are done with the Massing tools, as combinations of various geometric shapes made using extrusions, blends, sweeps, and revolves Again, with massing, the tools need to be flexible and not constrained to a specific use case In Revit, the same set of primitive form making tools is available when making massing geometry Figure 6.22 shows a massing study using Revit form making tools

Principles of Modeling Techniques

As we’ve mentioned, there are four basic form making options in Revit With these forms you can create almost any shape you need for various scales of design, from large scale massing studies, down to sink faucets By combining forms, and using forms as subtractive elements, nearly any-thing can be modeled in Revit The four primary forms are:

◆ Extrusion

◆ Revolve

◆ Sweep

◆ BlendAll of these are accessible in a few places:

◆ The Family Editor when selecting Solid or Void shape (Figure 6.23 A)

◆ Under the Modeling Tab, when you select the Create Tool, Solid or Void (Figure 6.23 B)

◆ Under the Massing Tab , when you select Create Mass, Solid or Void (Figure 6.23 C)44831.book Page 172 Friday, October 12, 2007 12:31 AM

Figure 6.22

Early Massing Concept Studies

Figure 6.23

The (A) Family Editor, (B) Modeling tab, and (C) Massing tab all enable you to create solid or void forms, which you can then model by any of the four basic techniques

Images courtesy of Gensler

Image courtesy of RMJM Hillier

174 CHAPTER 6 MODELING PRINCIPLES IN REVIT

Selecting Solid Form or Void Form from any of these toolbars displays the options shown in Figure 6.24

Figure 6.24

Solid and Void sion, Blend, Revolve, and Sweep options

Extru-Extrusion

Extrusion is the simplest of all modeling transformations and it’s based on a closed 2D sketch (shape) that is given a thickness value The thickness is always perpendicular to Work Plane of the sketch (Figure 6.25)

Figure 6.25

An extrusion is a 2D sketch shape with depth added

The Properties of an Extrusion allow you to set the thickness of the extrusion as well as an offset value from its Work Plane

Extrusion start Thisdefines where the extrusion starts and has a default of 0, but it can have any positive or negative value The effects of this parameter are shown in Figure 6.26

Figure 6.26

(A) “Extrusion start” is set to 0; (B) has a posi-tive value and the ex-trusion starts above the Work Plane;

(C) has a negative

val-ue and starts below the Work Plane

Extrusion end This feature defines the end of the extrusion relative to the Work Plane This value can be positive or negative The default is set to 1’-0” (25mm) The total thickness of an extrusion is the difference between the ”Extrusion end“ and ”Extrusion start“

When an extruded element is selected, check the Options bar for relevant options:

C

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Edit This feature takes you back to sketch mode so that you can make changes to the lying shape Once you have changed the shape, don’t forget to click on “Finish Sketch”.

under-Depth Depth defines the value of the extrusion depth—this value can be positive or negative

Visibility Visibility defines which view types or levels of detail you want the extrusion to be visible Figure 6.27 shows that the selected extrusion will be visible only in Plan and Reflected Ceiling Plan Views, and only in Medium and Fine Level of Detail

Figure 6.27

Forms can be made visible/non-visible in different views and at different levels of detail

Edit Work Plane This feature allows you to change the Work Plane of the extrusion Note that

a new Work Plane is only valid if it is parallel to the one that you wish to change

Figure 6.28 demonstrates how a Furniture Element can be constructed basically from two sions that create the entire shape Tip: to make the lower element hollow the sketch needs to be double (a sketch in a sketch)

extru-Figure 6.28

A cozy lounge chair made of two simple extrusions