Productivity Corner: MicroStation's 3D Capabilities, Part 1

15 Jan, 2005 By: James Dyer Cadalyst

Get to know the basics of creating, editing and viewing 3D models

This month's Productivity Corner column is Part 1 of a two-part series focusing on some of MicroStation's 3D concepts and functions.

MicroStation provides a comprehensive set of tools for creating, editing and presenting 3D geometry. This month we will cover the universal concepts associated with working in 3D within MicroStation. These include creating, editing and viewing 3D models. The great thing about working in 3D is all the 2D drawing and viewing tools you already use in MicroStation can also be used in a 3D model. Additionally, MicroStation offers a number of 3D-specific viewing and drawing or construction tools that simplify working in 3D.

General 3D Concepts
You exist in a 3D world wherein you can move and look in any direction. The designs you produce represent physical 3D structure. However, most people today continue designing these 3D objects in a 2D environment -- that is, they are representing 3D objects with 2D drawings. With MicroStation's 3D tools, it is easy to produce accurate 3D models of designs. Viewing a design from any direction and even moving inside the design could not be easier. Using MicroStation's visualization tools, you can produce high-quality images, walkthroughs or even animations of the design at any given time.

The transition from 2D to 3D design is a natural event; with very little effort you could create 3D models using the 2D tools you use every day. For example, you could create a 3D model using only the Place Block and Place Shape tools to construct each face of the object. To create a more complex model, however, you would need to use several of the 3D tools.

Before we explore the 3D creation tools, we need to familiarize ourselves with the 3D modeling environment and the basic viewing tools.

The Design Cube
MicroStation allows you to create 2D and 3D models within a single DGN file. Each model is a separate entity within the DGN file.

Figure 1. 2D coordinates are expressed in the form of (x, y).
With 2D models, your work is performed on a design plane, similar to a sheet of paper. All 2D geometry is therefore drawn on the active design plane. Locations on the plane are defined by x- and y-coordinates (figure 1). Of course, you can zoom in or out as required to work on small or large areas. To visualize your design more effectively, you often need to rotate the view to a desired orientation.

With 3D models, the 2D design plane becomes a three-dimensional cube, known as the design cube. All geometry is therefore drawn within this design cube. Locations within the cube are defined by x-, y- and z-coordinates (figure 2). When working within a 3D model, you can

Figure 2. 3D coordinates are expressed in the form of (x, y, z).
still create 2D geometry at any defined orientation. Within 3D models, you can place a block horizontally, vertically or at any other required orientation within the design cube. Similarly, you can view your design geometry from any direction. Think of the design cube as a transparent box in which the design is placed. The ability to rotate the view about any axis allows you to view your design from any direction. Additionally, you can place your viewing point anywhere inside the design cube, allowing you to work on or view specific parts of the model.

In the 3D seed files provided with MicroStation, the global origin is located at the center of the design cube and assigned the coordinates (0, 0, 0,).

View Volume
Within MicroStation each viewing window allows you look at any portion of the design cube. In a 2D model, each view window displays an area of the design plane. On the other hand, when working in a 3D model, each viewing window displays a volume of the design cube. This representation is often referred to as the view volume or display volume -- that is, each view window has a display area and a display depth.

This display depth can be limited by clipping planes placed before or behind the model, which restrict the view to a slice of the design cube. When clipping planes are enabled, any element not contained within the front and back clipping planes of the view will not display. Be careful: It may appear as if you have accidentally deleted elements, as no amount of zooming will make them visible. Those elements are simply outside the display depth of the current view.

The standard view volume is defined by the size of the view, represented by your window area; the front clipping plane and the back clipping plane will define the display depth (figure 3).

Figure 3. View volume with the front and back clipping planes.

Remember, nothing will be visible in front of the front clipping plane and nothing will be visible behind the back clipping plane. Only those elements entirely or partially between the clipping planes will be visible. Similar to the Window Areas function, whereby you select a discrete area of a view, Display Depth allows you to select a discrete slice or depth of a view.

If required, you can disable or enable either or both clipping planes in one or more views. You can do this using the Clip Back and Clip Front settings in the View Attributes dialog box, which you can access through the Settings pull-down menu.

Clip Volume
With MicroStation, you can apply a clip volume to specify a defined volume of the 3D model that is to be displayed in a view. This can be very useful when working on a small portion of a larger model. In such instances, set your view to display only the portion of the design that you are working on. Therefore, when you fit the view, the system will display -- and snap to -- only those elements contained within the defined volume.

When a clip volume is active in a view, you still can use clipping planes to select a slice of the view. If there is a clip volume applied, it can be disabled or enabled in a view using the Clip Volume setting in the View Attributes dialog box.

Clip Mask
In a similar fashion a clip mask may be applied, which lets you define a volume of your model that you do not want to display in a given view. Again, this can be useful to remove the display of geometry that is not required for the section that you are working on. Additionally, a clip mask may be defined within the boundary of a clip volume. That is, you can define a clip volume to display just the region that you want to see or work on. Within this region, you then can define a clip mask to remove the display of part of that clip volume.

Display Depth
As you can imagine, each MicroStation 3D view has both a display depth and an active depth.

Within each view, the display depth will define how much of the overall depth of the view is to be displayed. This can be controlled by the location of front and back clipping planes. These clipping planes are parallel to the view with the front clipping plane nearest to you and the back clipping plane farthest from you.

Active Depth
The space between the clipping planes defines another plane at the active depth of the view. The active depth defines the depth at which data points are placed by default. So, if you placed data points in a view without first snapping to another element, they would lie on a plane at the active depth value. The active depth plane always is located within the display depth of a view. Be careful: Its value may change when you fit the view.

MicroStation's 3D creation, editing and viewing tools are both easy to use and powerful. These concepts will become clearer as we exercise them during next month's journey through MicroStation's tool sets.

Until next time -- enjoy MicroStation!

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