User Guide
User Guide
User Guide
User Guide
User Guide
User Guide
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This section introduces the basic concepts related to working with 3D models.
3D DGN files consist of a design cube in which you work. The design cube represents a 3D DGN file's total volume, in which points are defined with x-, y-, and z-values, or coordinates. Points can be placed anywhere within the design cube, and are not restricted to a single plane as is the case when you work in a 2D DGN file.
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The 2D design plane (top) and 3D design cube (bottom) | |
Design cube coordinates are expressed in the form (x,y,z). The global origin in the 3D seed files provided with MicroStation is located at the exact center of the design cube and assigned the coordinates (0,0,0). Any point in front of (or above) the global origin has a positive z-value and any point behind (or below) it has a negative z-value.
The view volume (sometimes called the display volume) is the volume of the design cube that is displayed in a 3D view. In most cases, only a part of the design cube is displayed in a view.
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View volume. “A” denotes the window area (hatched). “D” denotes the Display Depth, bounded by the front “F” and back “B” clipping planes. The large cube shows the design cube, part of which is displayed in each view. | |
Any elements, or parts of elements, not contained in the view volume are not displayed in the view. Unless a clip volume has been applied to a view, the view volume is bounded by the window area, and its Display Depth.
You can set the clipping volume of a 3D view such that only the region of interest is displayed and you can snap to only those elements that are located within the defined clip volume of the view. Similarly, you can apply a clip mask to a view, where only those elements located outside the clip mask are displayed. When a clip mask is used inside a clip volume, the only elements that will display in the view are those that are located within the clip volume, and outside the clip mask. Additionally, if you use the Fit View tool, only those elements within the clip volume are considered. This simplifies working on discrete portions of large and/or complicated 3D models (see Clip Volume and Clip Mask view controls).
At any time, in a view, you can toggle on/off the view display restrictions of the front and/or back clipping planes. Similarly, you can toggle the clip volume, if one has been applied. Three settings in the View Attributes dialog box let you do this:
Clip Back — if on, a back clipping plane is active in a view.
Clip Front — if on, a front clipping plane is active in a view.
Clip Volume — if on, and a clip volume has been applied to the view, the view volume is restricted to the defined clip volume.
The distance from the front to the back of a 3D view is its Display Depth. This depth is bounded by clipping planes, unless they have been disabled in the View Attributes dialog box. When clipping planes are on:
The front clipping plane is nearest the viewer.
The back clipping plane is farthest from the viewer.
Elements in front of the front clipping plane, or behind the back clipping plane, are not displayed in the view. This applies even if they are within its viewing area, regardless of how far the view is zoomed out. In other words, the front and back clipping planes define a “slice” of the total volume of the design cube. Only elements located within this slice can be displayed in a view.
When a clip volume has been applied to a view, and Clip Volume is enabled (in the View Attributes dialog box), then this is the maximum volume of the design cube that will be displayed in that view. Clipping planes can be set that reduce this volume, but they have no effect if they are set outside the clip volume.
The Active Depth in a view defines the position of a plane, parallel to the screen, on which data points are entered by default. The Active Depth is perpendicular to, and is measured along, the view's z-axis. For this reason, it is sometimes referred to as the “active z-depth.”
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Active Depth, denoted by “AZ.” “x,” “y,” and “z” denote the View axes. “F” and “B” denote the front and back clipping planes, respectively. | |
For example, suppose you are modeling the interior of a multi-story building. You can complete the details on one floor at a time in the top view by setting the Display Depth and Active Depth to each floor successively. An even better method is to create a 3D clipping element (such as an extruded block) that encloses a single floor of the building and then use the Clip Volume view control to “hide” all other geometry. With this set up, to view any particular floor, you would move the clipping element to the level of the floor that you wanted to work on, and the display volume would change accordingly.
You set the Active Depth with the Set Active Depth view control . Also, you can change the Active Depth by completing a view manipulation — for example, Rotate View, Fit View, Change View Perspective — for which you snapped to an element for the first data point.
 | A view's Active Depth always lies within its Display Depth. |
 | Although Active Depth is a very powerful concept, MicroStation also lets you position points away from the Active Depth. For example, using AccuDraw in 3D, you can work at a particular depth without having to first set the Active Depth. For more information, see Drawing in 3D. |
If you rotate a view to a standard orientation, the view orientation displays, along with the view number, in the view's title bar.
In 2D, the design plane is parallel to the screen and, in effect, you view the model from above. The default (unrotated view) in 2D is like a Top view with its orientation such that:
The x-axis is positive from left to right (horizontally).
The y-axis is vertical, and positive from bottom to top (vertically).
In a 2D model, you rotate a view about an imaginary z-axis, which is perpendicular to the screen. No matter how you rotate a view in 2D, effectively, you still view it from above.
In 3D, since you can rotate views about three axes, rather than just one, there are six orthogonal orientations, each of which corresponds to a standard orthogonal view: Top, Bottom, Left, Right, Front, or Back.
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The faces of this cube correspond to the 3D orthogonal views. The cube is displayed here in an Isometric view. | |
A Top view displays the model from the top:
the xy plane is parallel to your screen (as in a 2D model).
x is positive from left to right (horizontally).
y is positive from bottom to top (vertically).
z is positive toward you, perpendicular to the screen.
A Front view displays the model from the front:
the xz plane is parallel to your screen.
x is positive from left to right (horizontally).
z is positive from bottom to top (vertically).
y is positive away from you, perpendicular to the screen.
A Right view, displays the model from the right:
the yz plane is parallel to your screen.
y is positive from left to right (horizontally).
z is positive from bottom to top (vertically).
x is positive toward you, perpendicular to the screen.
Similarly, the remaining orthogonal views display the model from the Left, Bottom, and Back.
There are two other standard views — Isometric and Right Isometric. These views are rotated so the three faces of a cube orthogonal to the design cube axes are equally inclined from the screen surface.
Standard view |
Faces in front |
|---|---|
Isometric |
Top, Left, and Front |
Right Isometric |
Top, Right, and Front |
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Isometric view (left) and Right Isometric view (right) | |
Working in 3D, in every view we always have at least two coordinate systems to work with — the DGN file coordinate system and the view coordinate system. Only in a Top view, do the two coordinate systems align exactly. When we rotate a view, in reality we are repositioning our view “camera” to let us see the model from a different direction. Thus, when we rotate a view, the DGN file's axes rotate with it. Each view's axes, on the other hand, are relative to the view (or, if you like, the screen) and the following always applies for view axes:
The x-axis is horizontal and positive from left to right.
The y-axis is vertical and positive from bottom to top.
The z-axis is perpendicular to the view (screen), and positive toward you.
Thus, you can place elements relative to the DGN file coordinates, or relative to the view coordinates. When you use AccuDraw, this is easier to understand as its compass gives you a visual indication of the drawing plane in which you are working.
Elements in 3D models must be displayed on the screen, which is planar.
In a view with parallel projection, each element is projected to the screen along a line parallel to the view's z-axis. Although parallel projected views make drawing easier, they lack realism because elements have the same relative size regardless of their depth in the view. With parallel projection it can be difficult to decipher the orientation of the model.
In a view with perspective projection, elements at greater depths appear relatively smaller, enhancing realism. A view with perspective projection is also referred to as a camera view.
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Example of parallel projection (left) compared to a perspective view (right) | |
In a 3D DGN file, you can define the orientation of the grid to suit the task at hand. Once you define a grid, Grid Lock works as expected and input points are constrained to the grid points. The Grid Orientation is controlled from the Grid section of the DGN File Settings dialog (select Settings > Design File). Options are:
View — Grid always aligns to the view and passes through the global origin.
ACS — Grid aligns to the active ACS.
Top — Grid aligns to a “Top” view. It extends along the X and Y axes from the global origin.
Right — Grid aligns to a “Right” view. It extends along the Y and Z axes from the global origin.
Front — Grid aligns to a “Front” view. It extends along the X and Z axes from the global origin.
Added to these options, is a key-in that lets you rotate the grid about (its) Z-Axis. This key-in, ACTIVE GRIDANGLE <value> is included specifically to provide compatibility with AutoCAD, which supports only a grid in the XY plane, but can include a rotation angle.
When you define a grid to align to an ACS or a view orientation, it will rotate with that view, or display with perspective in camera views.
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Perspective view displaying the grid with Orientation set to Top | |