Principles of Modeling in Revit |
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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
- Blend
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| All 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)
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Figure 6.22
Early Massing Concept Studies |
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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 |
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| 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 Extru-sion, Blend, Revolve, and Sweep options. |
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| 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 |
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| 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 This defines 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 |
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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: |
Edit This feature takes you back to sketch mode so that you can make changes to the under-lying shape. Once you have changed the shape, don’t forget to click on “Finish Sketch".
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. |
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| 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 extru-sions that create the entire shape. Tip: to make the lower element hollow the sketch needs to be double (a sketch in a sketch). |
Figure 6.28
A cozy lounge chair made of two simple extrusions |
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Directions in a Reference Plane
The direction in which one draws a Reference Plane determines which way is positive and which way isnegative.
These images demonstrate in plan view how the different direction in which the Reference Plane wasdrawn affects the direction of the extrusion:
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It is not easy to remember which way you drew each reference, thus we suggest this tip: Name eachReference Plane you create. If you do that, when the Reference Plane is selected you will see the name ofthe Reference Plane, and it is always placed at the END of the direction in which it was drawn.
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| When you use the faceof an element as a Work Plan (rather than Reference Planes) as shown in Figure 6.29, the direction of the extrusion will depend on whether you are making it a solid or a void shape |
When you sketch a shape that is going to be a Void, the void will be extruded positively toward the interiorof the object that we used to define the Work Plane.
When you add a Solidshape, the shape will extrude positively away from the exteriorof the object face (Figure 6.30). |
Figure 6.29
A void extrudes into the solid face |
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Figure 6.30
A solid extrudes away from the solid face. |
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| Revolve |
| Revolve takes a 2D profile and rotates it around an axis. A revolve is composed of two elements: a 2D profile (think of this as a cross section) that will define the surface once it is revolved, and an axis that the profile will revolve around. As with extrusions, the profile sketch must be a closed loop of lines for the revolve to be valid. The bollard shown in Figure 6.31 is an example of a revolved form |
Figure 6.31
A revolve consists of a closed loop sketch and an axis of rotation |
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| A revolve will follow a full 360 degree path by default. In the properties of a revolve you can adjust this angle, so that the profile can appear open, as shown in Figure 6.32. |
End angle This positions the sketch relevant to the Work Plane of the end of the revolution.
Figure 6.32 shows a revolve with an end angle set to 270° |
Figure 6.32
End angle is set to 270 |
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Start angle This positions the sketch relevant to the Work Plane at the beginning of the Revo
-lution. By setting the Start Angle to a value other than 0, you can get shapes like that shown in Figure 6.33. |
Figure 6.33
“Start angle" is set to 90° and ‘End angle’ is set to 270°. |
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When an element that is revolved is selected, you will find the following Tools in the Options Bar:
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These are similar to the options available when selecting other modeling forms. You can change the sketch that you used to execute the revolution with, set the Visibility, Edit the Work Plane or Rehost the form to another plane.
To understand the how sketches create revolution shapes, we will look at three different results based on three different types of sketches. Figure 6.34 shows a standard revolution made out of one closed loop of lines. Figure 6.35 shows a revolve made out of two closed loops, where one loop is a subractive element; and Figure 6.36 shows another sketch with two closed loops, where each loops is an additive element |
Figure 6.34
One closed loop of lines revolved around an axis |
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| A revolve can be composed of multiple closed loops to define the profile sketch. Keep in mind that each sketch must not intersect another sketch, or the sketch will fail, and Revit will warn you when you try to “Finish Sketch". Depending on the positioning of the different loops, you can achieve different results, as shown in the Figures 6.35 and 6.36: |
Figure 6.35
In this example, the two closed loops of lines are placed one inside the other. Fol-lowing the principle of sketch based design, the inner loop creates a hole in the first loop |
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Figure 6.36
The two loops are independent of one another and thus the resulting revolution creates two solid shapes. |
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| A common example of a revolve form is shown in Figure 6.37. The profile defines the cross section of a dome (cupola) roof. By rotating this profile around the center axis, a dome form can be generated. |
Figure 6.37
The profile is revolved around the center axis, resulting in a dome form |
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The Rule of the Axis
None of the shapes that are to be revolved can intersect the axis of the revolution. They can howeverhave an angle different than 90 degrees to it and can be offset from the axis. |
| Another example of a revolve is this door knob (Figure 6.38), where the the cross section is drawn then revolved around an axis: |
Figure 6.38
A revolve can be used to create elements such as door knobs as well |
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| Sweep |
A Sweep is conceptually similar to an extrusion, but you define a path for the extrusion profile to
follow. The resulting form is generated by sweeping the profile along path segments. The profile is always swept perpendicular to the path segment it follows.
A sweep is defined by two sketches: the Path and the Profile that you sweep along the Path. The path can be drawn on any Work Plane, and the profile will always be drawn perpendicular to the path. The first segment of the path you draw determines the default Work Plane for the profile sketch. To change the default location of the profile sketch plane, delete the line segment of the path that hosts it—the profile plane will jump to next available line segment in the path. Figure 6.39 shows a swept form, along with the path and profile used to create it |
Figure 6.39
Example of a sweep. In the sketch, the dashed rectangle is the profile plane—always perpen-dicular to the path |
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| Defining the Sweep Path |
| You can make a path by either picking existing geometric edges to create new lines, or by or draw-ing lines. These options are available either from the design bar: |
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| or the Options bar: |
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Sketch 2D Path allows you to draw the path using the various draw tools to make lines. You can use the pick command to pick edges and lines from the other elements to speed up creation:
Pick Path allows you to select existing lines or edges of geometry as the path for your sweep. With this method you create a dependency between the swept element and the object that you picked for edges to define the path. Thus, when the geometry of the referenced object changes, so too will the swept element. We strongly recommend working in a 3D view when using this method to make it easier to understand the relationships and effects of changing geometry (Figure 6.40). |
Figure 6.40
Example of a sweep-ing path that is created by picking existing edges of a solid geom-etry (in this case a wall opening). Should the opening change its size, the sweep will also change because of the dependency estab-lished with the pick method. |
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| Defining the Profile |
A profile can be created using one of two methods: by drawing the profile, or by using a loaded, pre-defined profile. These options are shown in the options bar when the sweep command is acti-vated. The default is <By Sketch> and lets you draw the profile using standard draw tools. You can also select a profile from the pulldown list of profiles that can be loaded into the project/family. This method is applicable in cases where you will need to sweep the same profile on many paths. For example, you would first create a 2D profile family using the Profile (imperial) M_Profile (met-ric) template. The profile has to be a closed loop of lines. You then save the profile on your hard disk and then load it in your project.
Once you’ve made a sweep profile, the profile will be available in the dropdown list in the Options bar
Figure 6.41 shows the Options bar with both options. |
Figure 6.41
The default method for creating profiles is by sketching (top). You can also load pre-made profiles and use those (bottom) |
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| If you use a loaded profile, you are given controls to position the profile relative to the X and Y axes (Figure 6.42). These values are distances from the point of insertion of the profile (the inter-section of the two Reference Planes in the family editor) and the point of reference of the profile and the path (the green cross). You can also rotate the loaded profile by adding a value under the “Angle" option (Figure 6.43). The Flip button will mirror the profile, if you need it. |
Figure 6.42
Offsetting the profile from the point of ref-erence of the path. In this profile, the cross-ing of the references in the family editor was set to the lower left corner of the profile. Thus, the offset values start from that point. |
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Figure 6.43
Angle of rotation is ap-plied to the profile that is to be swept |
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| Once a sweep is created, you can always change the values that are available in the Properties of the sweep: |
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The advantage to using pre-made profiles is enormous. Figure 6.44 illustrates a concrete example of a sun shading family that needs to be edited.
If you drew your profile manually and then used the Copy Multiple command to repeat the shade, you will need to change each shade separately to apply a new profile. If you had drawn the shape as a loadable profile family and loaded it into the family, you’ll only need to change the profile family once and re-load it. All instances of the profile will update automatically when re-loaded. |
Figure 6.44
Sweeps can be used to create a sun shade. |
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Putting the Sweep Tool to Work
Here are some real life scenarios in which the Sweep tool is very handy. We’ll let the pictures do most ofthe talking.
First consider the modern shower fixture in the bathroom shown here:
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This design was created as a simple sweep on a circular path.
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The architectural example shown here demonstrates another use of sweeps, to create a highly specific wallshape. The retaining wall was created as an in-place wall using the Create function and the Sweep method.
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| Trajectory Segmentation |
| This option (Figure 6.45) provides a way to segment smooth arcs into linear segments. This can be useful when rationalizing a form into planar, constructible elements. When the option is checked, it makes the parameter Maximum Segment Angle active. The value you set will define the maxi-mum value of the angle between two segments of the arc. The smaller that value, the higher the number of linear segments that will replace the arc. Figure 6.47 shows the effects of this parameter. |
Figure 6.45
Sweeps can be seg-mented using the “Trajectory Segmen-tation" parameter |
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Figure 6.46
An arc path can be segmented using the Maximum Segment Angle parameter |
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Blend
A blend creates a form by connecting two different 2D shapes on two different planes along a linear path (Figure 6.48). The distance between the two shapes—the base and top, is what defines the depth of the blend. The two shapes for the top and base of the blend do not need to be the same shape or have the same number of segments. Revit can even blend arcs into linear segments.
When the top and base shapes are the same, the resulting form will look exactly like an extrusion or sweep along a single, linear segment. You can think of a blend as extrusion with two sketches—one for the base, and one for the top. |
Figure 6.47
A blend is created from two sketches that blend together along a linear path |
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| The properties of a blend are very similar to those of an extrusion. You can set the Blend Depth as well as the offset from the work planes on which the shapes will be drawn. |
First end This defines the offset of the base shape relevant to its work plane. This value can be
negative or positive. The default value is set to 0.
Second end This defines the offset of the top shape relevant to the work plane on which
the blend is drawn. This value can be positive or negative. The default is set to 1’ 0" (250mm).
The total depth of the blend is the resulting value between the First End and the Second End.When a blended element is selected, you will find new tools in the Options Bar:
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| These are the same as the options for extrustions, with addition of two other features that take to the sketch of the base or top of the blend. Edit Base: you can always go back to the base sketch by selecting this option and redefine its shape if needed. You will need to “Finish sketch" to exit that option. |
Edit Top Enters sketch mode where you can modify the top sketch.
Edit Base Enters sketch mode where you can modify the base of the sketch. |
| Whenever you select one of those two options, the Options Bar will change as well as the design bar, as shown in Figure 6.48 |
Figure 6.48
Options in the Design bar depend on wheth-er you are editing the base (A) or the top (B) of the blend |
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As you can see, when creating blends there is not one single work plane—this means that the two sketched shapes are always on work planes that are parallel.
Vertex connect is a tool specific to blends, and it shows up in the design bar when editing the
blend sketch. This tool allows you to set the connection between the vertices that the two shapes have. Manipulating the vertexes will produce different results in the final blend.
When you click on the Vertex Connect tool, you will see graphic controls indicating existing con-nections between the vertexes of the blend shapes.
There are two different things you can do here: |
Twisting After selecting Vertex Connect, you will find two tools called Twist in the
Options bar |
| iNSERT iMAGE |
| These control the number of twists between the two shapes. Figure 6.49A shows a basic blend between two 45 degree oriented square shapes. Figure 6.49B shows one additional twist and Figure 6.49C yet another additional twist. |
| Editing Vertices |
| This is another way to affect the blend in order to arrive at alternative shapes. By clicking one of the open blue circle controls that appear when you first select the Vertex Connect tool, you’ll have the ability to change the direction of the vertexes by clicking on the control. Once you change the connection point, the circle will be filled in solid blue (Figure 6.51B) and a line will be drawn show-ing a preview of the connection from one vertex to another. Revit will connect the vertexes from the base shape to the top shape in automated way with each click. But each of the vertexes has an option to be connected to the top vertex that lies to the right of it, or left or both. The example shown in Figure 6.50 demonstrates how the same blend with the same base, top, and depth all look differ-ent depending on the vertex connections. |
Figure 6.49
The forms shown can be a tower shape or a table leg: various looks for the same element depending on the number of vertex con-nections or twists |
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| Troubleshooting Blends |
When the base shape of a blend has the same number of vertices as the top shape, the results are pretty much predictable. But often the number is not the same and you may not get the results you expect or desire. A few tips to consider when working with more complex blends:
If one of the shapes is a circle, you might want to break it up into segments to get additional ver-tex points so that you arrive at a shape you need, as shown in Figures 6.51 and 6.52 |
Figure 6.50
Changing vertex con-nections will result in different blend forms |
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Figure 6.51
A standard blend you will often see, with base shape square and top shape circle. |
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Figure 6.52
The same shapes with the circle split into 4 segments to add 3 more vertices. In ex-ample A, the vertex points are orthogonal; in B they are rotated 45 degrees. Note the difference in the results. |
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Creating a Lamp with Blends and Sweeps
A real-world application of blends and sweeps can be seen in the Revit lamp family illustrated here
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The shade is constructed using a blend between a segmented circle for the top (A), and a more complexseries of arcs for the base (B).
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The top sketch has been divided into many segments to match the number of vertexes of the base. Thisfile can be found in the Chapter 6 folder on the web site if you want to explore it some more on your own(PS Lamp.rfa).
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The legs of this lamp can be made using sweeps. A void extrusion was used to cut the bottom of the legshorizontally so that it sits flat on the floor.
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| Examples of Blends in Practice |
| The following shapes (Figure 6.53) are inspired by the sculptor and designer Isamu Noguchi’s lamps, but as you can imagine, they could just as easily represent a lamp, a column, or an entire shape of a building. They are constructed as simple combinations of connected blends. |
Figure 6.53
A series of blends used to form a more com-plex form. |
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| The blend sketches cannot contain more than one loop of closed lines. If your intention is to cre-ate something like the lamp shade shown in Figure 6.54, you will need to add a void. If you try to make such a shape, Revit will give you a warning message stating that “more than one loop is not allowed." |
Figure 6.54
This blend sketch with multiple loops is not allowed and would generate a warning message. |
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| To obtain the result needed, you will need to first create a solid blend and then a second one, done with void that has a smaller radius, as shown in Figure 6.55 |
Figure 6.55
A lampshade can be made by creating a void blend that is smaller than the solid blend. |
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Consider Your Options
Before making a digital model of your design, whether it is the shape of an entire building, a portion ofspecially modeled wall, a front desk or a door handle, you need to analyze and think about the basic geo-metric shapes that are used to create such a form. Is your object best modeled as an extrusion. A blend.A sweep. A blend with a void cut in it. Think carefully how the element is made, how it is assembled,and the tools that Revit provides to plan your modeling strategy. |