3D AutoCAD 2010 for Starters and Others. . .
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3D AutoCAD 2010 for Starters and Others. . .
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Saturday January 02, 2010
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Wire Frame Models
Creating complex 3D wire frame models can be more difficult and time-consuming than creating their 2D views. Nevertheless, knowing and understanding some of the wire frame techniques will greatly help you when graduating to surface or solid modeling. When you draw 3D wire frame objects you draw just like when you draw 2D objects, put them on appropriate layers and use 3D coordinate entries and precision techniques to specify each point and distance. Remember, the better you understand wire frames the better you understand 3D solid modeling. A wire frame model is like a skeleton of a 3D object that is drawn with only points, lines, circles and arcs (curves) representing edges of the model but no surfaces. They are called wire-frame models because they appear to be made of wires and everything in the background is visible because you can see right through them. This does not create a very realistic effect in the visualization of the 3D object.
Figure 1 The Wire Frame appears to be made out of wires and may not create a very realistic view of the model. Wire-frame models have no volume or mass and the HIDE command cannot be used to hide background elements. Since there are no surfaces you can’t shade them. To draw a 3D model of a cube as a wire frame, you need to draw twelve lines by specifying 3D coordinates for each of its points. Because each object that makes up a wire frame model must be independently drawn and positioned, this type of modeling can be the most time-consuming. Once you have a wire frame model it can be used as the starting structure for a surface model by simply adding surfaces.
Drawing Wire Frame Models There are different construction techniques but there are not a lot of practical applications for wire frame models. However, once you are working with solid models, AutoCAD let’s you automatically create a wire frame display of your model to modify the model in wire frame mode. Understanding the wire frame will then make make viewing and changing a solid model a lot easier. The command sequence for drawing 3D wire frame segments with the LINE or 3DPOLY command is the same as for drawing 2D segments with the LINE command. The difference is that you specify 3D coordinates instead of 2D ones and that the 3DPOLY is limited to straight line segments. To reduce and save wire frame construction time: · Use appropriate LAYERS AND COLORS to organize the model to reduce the visual clutter of the model. · Instead of flip-flopping back and forth between views, use VIEW PORTS and automatically generate standard orthographic and isometric views to make visualizing the model and selecting objects easier. · Use the UCS to create other work planes (the XY plane of the UCS) to orient objects in other than the current plane more convenient and practical.· Use OSNAP whenever possible to ensure the precision of your model. The Apparent Intersection option is very useful to snap to an imaginary intersection of two objects that appear to intersect, but actually don’t intersect because they lie in different planes. · Use COORDINATE FILTERS to drop perpendiculars and easily locate points in 3D based on the location of points on other objects. · Use the MOVE, COPY, ROTATE and MIRROR command to place object to their proper 3D location after you create it. · Use the LINE, PLINE, SPLINE and 3DPOLY commands and enter 3D coordinates that define the X, Y and Z location of the object. Basic wire frame models can be created using VIEWPOINT, allowing to display and view the current 2D model from preset viewpoints or at any angle in a 3D view, and then using the basic 2D commands such as the LINE command to construct the object along the z-axis using OSNAP features such as Endpoint, Midpoint etc. Wire Frames can also be constructed using FILTERS. In addition, models or shapes can also be constructed as EXTRUDED or THICKENED shapes using the ELEV command giving a base elevation and then changing its properties by giving them thickness to a 2D shape as explained later. Be aware, the EXTRUDE command described herein shall not be confused with the actual “EXTRUDE” command that creates solid extrusions for solid models.
Viewpoint Wireframes This method uses preset views to display a 3D model. Each object that makes up a wire frame model can then be independently drawn either in the standard 2D view or in 3D space. To create a 3D wire frame model footprint, apply the following procedure: 1. Open the 3D Starter or the AutoCAD default drawing and use the My 3D Drafting or the default workspace and save the drawing. 2. Select TOP from the View toolbar or enter PLAN and accept <current>. 3. Select the 2D Wireframe option from the Visual Styles toolbar and use the Zoom- All option and turn the GRID to OFF. Make the 10 OBJECT layer current and select an appropriate color. 4. Use the LINE command and draw the footprint of the 3D wire frame model in the center of the graphics area. 5. Select SE Isometrics from the View toolbar to display the footprint of the 3D wire frame model. The model is now displayed in 3D and viewed from the South East corner and somewhat above the x-y plane. See Figure 2-2 View 1. Zoom in or out for easier viewing. If you want to return to the previous 2D display select TOP from the view toolbar or enter PLAN and then select <current>. Notice that all your object lines drawn on the 2D x-y plane are still shown on the same x-y plane with no elevation added in the z-direction. The object drawn is still a 2D model. Turn on the GRID to make it easier to verify that the model resides on the x-y plane. See Figure 2 View 1.
The origin of the current (world) co-ordinate system is also displayed and now displays the z-axis to give you a sense of the 3D space. Notice the small square where the three axes meet, indicating the World co-ordinate system is current. Also notice that the z-axis doesn't have an arrow at its end, so that you can easily distinguish it from the X and Y axes.
Figure 2 Wire frame models in SE Isometric view can be constructed using basic 2D commands with 3D coordinates. To create the cylindrical 3D wire frame model by copying the footprint vertically up in the z-direction (adding height) and then connecting vertical edges, apply the following procedure: 1. Select COPY and then select the footprint object. Use OSNAP to select a corner point of the 2D footprint as the base point. You must now enter 3D coordinates @ 0, 0, 4 as the offset for this point of the original footprint to duplicate the footprint in 3D space 4 units above the x-y plane. This coordinate entry indicates NO movement in either the x- or y-axis but a 4 unit movement in the z-axis to create the height of the model, since we want the model created right-angle up in the z-direction. See Figure 2 View 3. Entering @0, 0,-4 instead would copy the footprint 4 units vertically right-angle down. Entering @0, 1, 4 instead would place the footprint at a slight angle to the right. 2. Connect the endpoints between the two shapes using the LINE command and OSNAP to form all vertical lines or edges in this 3D view from the corners of the original foot print to the copy of the footprint 4 units above. Since all vertical lines are 4 units long, you may use the COPY command for speedier placement of these vertical lines. See Figure 2 View 2. Alternate Entering Options: Use COPY and ORTHO and then enter 4 as a direct distance for the z-axis dimension however, will move the footprint like entering the 3D coordinates, since you are in the x-y work plane where most of the 2D commands may still be used. If you use DYN there is no need for @ before the coordinates. If you use COPY and then move the foot print with the cursor will only transfer the footprint to a different location on the x-y plane. Use the LINE command and draw the shape again at the new level 4 units above the current x-y plane by using LINE → Ctrl+Right-Click → FROM → Pick lower left corner with OSNAP → @0,0,4 and then draw the shape again using ORTHO and direct distance entries. Use the LINE command and then place a 4 unit long vertical line using any of the corners on the footprint using ORTHO and direct distance entry and then use COPY to place a copy of the footprint to the end of this line using OSNAP. See Figure 2-2. View 2. This completes the wire-frame model. See Figure 2. View 4. It appears to be made out of wires with the edges forming the model and you can see right through the model. Viewing 3D Models When displaying wire frame models in preset views, edges are some times hidden from view being obstructed by other edges. See Figure 3. The NW corner of the model has two edges obstructing each other.
Figure 3 When using preset views, edges of the wire frame model may be hidden from view by other edges. Using the ORBIT command allows rotation of the model to modify the viewpoint. Use the ORBIT command to dynamically change your viewpoint to view an edged that may be obstructed by another edge. The ORBIT command can be invoked by entering ORBIT or 3DORBIT or 3DO at the command prompt or use the Constrained Orbit option from the toolbar. To view obstructed edges with the ORBIT command, apply the following procedure: 1. Invoke the ORBIT command.
2. The Visual Styles does not change but the color coded UCS icon is displayed temporarily while in the Orbit command. See Figure 2.
At the same time, the cursor changes
to a small sphere 3. Click and drag the Constrained Orbit “capsule” very gently in any direction and your viewpoint angle changes and displays the U-model at different angles. Explore different viewpoints and then display the model in a view so that the two vertical edges in the NW corner of the model no longer obstruct each other. See Figure 4.
Figure 4 Using the Constrained Orbit option provides an opportunity to rotate the model and view edges that are hidden or obstructed from view. 4. Settle on a view that displays the two edges of the U-model that previously obstructed each other in the NW corner of the model. If done correctly, all of the edges should be visible. This is then actually a view slightly off our original SE Isometric view. Use Esc to terminate the ORBIT command. 5. For faster ORBIT action, press and hold the shift key and then press and hold the mouse wheel (or middle mouse button) and then use the wheel to drag in any direction for viewpoint changes. This is also called the “SHIFT + Middle Mouse Button” method. To finish the rotation, just release the Shift key and mouse wheel. To return to the previous view select View Previous. 6. Save this view for later recall as “Step 3 Orbit”. Wire-frame models have no volume or mass and the HIDE command cannot be used. Since there are no surfaces you can’t shade them. 7. Save the drawing as Wireframe VPoint.
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