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TUTORIAL III

Using Paths for Smooth Profiles


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Step 1 - Creating the Path

To add the initial path for the profile pick Open Path from New in the Object Menu. Pick Object Select mode and the Marquee selection tool. Pick the open path object and then Pick Edit Path from the Mode menu. Notice that the ends of the path have changed to points, these are the initial control points for the path. In order to add some more we are going to fracture the path. Make sure the Marquee select tool is picked and draw a rectangle around the whole path. Pick Fracture from the Object menu, the path will now have three control points. Repeat this until there are nine control points.

The next bit is the essence of the object's design, i.e. the artistic bit. This involves moving and rotating the control points to achieve the required profile. For this tutorial use the list of co-ordinates below. The first point on the list is the upper most point in the TOP view. For each point the first column is the Position information and the second column is the Alignment information. In Edit Path mode pick each point and bring up the Object Transformation dialogue box. Check the Position check box and type in the co-ordinates for X,Y,Z, as shown in the first column. Then check the Alignment check box and type in the co-ordinates for X,Y,Z, as shown in the second coloumn.

Path Postion and Alignment Information

Points
Position
Alignment
1
5, 40, 0
0, 0, -180
2
7, 41, 0
0, 0, 0
3
6, 40, 0
0, 0, 0
4
6, 38, 0
0, 0, 0
5
6, 22, 0
0, 0, 0
6
12, 6, 0
0, 0, 0
7
12, -24, 0
0, 0, 0
8
10, -26, 0
0, 0, -90
9
0, -26, 0
0, 0, -90

Once this is complete the path should look like the one shown in Figure 1, below. If it is, select it in Object Select mode and save it as porfpath.iob. If not, check the points' co-ordinates against the table.

Figure for Step 1
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Figure 1


Step 2 - Creating the Sweepable Profile

Initially add a primtive plane. The properties for the plane are Width=10, Height=10, Horiz. Sections=1 and Vert. Sections =1. Select the plane in Object Select mode. Bring up the Object Transformation dialog box and check the Position check box. Type in 5,0,5 for X,Y,Z. With the plane still selected bring up the Object Transformation dialog box again and check the Position check box and the Transform Axis Only check box. Type in 0,0,0 for X,Y,Z. What we have done is move the plane axis to one corner of the plane. This is so that, during the next operation, the point at the corner when the axis is tracks perfectly to the path.

Select the plane in Object Select mode and the bring up the Extrude dialog box gif. Check the Along Path check box in the Method section and check the Align Y-Axis to Path check box. Type in 128 for the Number of Sections. The next thing to do now is delete the original path. In Object Select mode with nothing selected press the "Ctrl" and "n" keys. As the path was the first thing added it will be highlighted as being picked first. Press the "F1" key to select then delete it. Now select the extruded plane in Object Select mode and then pick Point Select mode. Also, Pick the Marquee Selection tool. Drag a rectangle around all of the point above the axis in the FRONT view, as shown below in Figure 2. Delete these points. Now pick Lasso Select mode gif. In the top view draw a lasso around all of the points on the outside of the object leaving all of the points which align exactly to the path unselected. This is shown in Figure 3. Delete these points. We now have the basic sweepable profile, so select it in Object mode and save it a baseprof.iob.

Looking at this profile you will notice that there are a lot of points that lie on straight edges. When the profile is swept these points will generate extra edges and faces without contributing to the detail. There are three areas where we can hand optimise the profile. These are the bottom, the neck and the body. Remaining in Point Selection mode pick the Marquee Selection tool. First drag a rectangle around all the points that form a straight edge on the neck. Then holding down the "Shift" key do the same for the base and the body. The selection to be made are shown in Figure 4, below. Delete these points. Now pick Add Lines from the Mode menu and join up the points to form the missing edges. The completed profile is shown below in Figure 5. Select this in Object Select mode and save it as compprof.iob.

Figures for Step 2
gif gif
Figure 2
Figure 3
gif gif
Figure 4
Figure 5


Step 3 - Sweeping the Completed Profile

Load in compprof.iob, if not already loaded. Select the profile in Object Select mode and bring up the Object Transformation dialog box. Check the Rotate and the Transform Axis Only check boxes. Type in -90,0,0 for X,Y,Z. What we have done is align the Z of the axis to be in the correct orientation for the sweep. Remember, the the profile is swept around the Z axis. With the profile still selected bring up the Sweep Controls dialog box. The propeties are Sweep Angle=360 and Number of Sections=48. Select the completed bottle, as shown below in Figure 6, in Object Select mode and save it as bottle.iob.

Figure for Step 3
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Figure 6


And Finally.......

There are two important things to bear in mind when using the methods described in this tutorial. Firstly, Always hand optimize the profile. Even if this only results in the removal of one point. That one point is multiplied up during the sweep adding many more edges and faces. Remember that Imagine has a edge limit. Secondly if the axis in incorrectly positioned you may find that the faces overlap or you get a hole where they should meet at a single point. Always check this.

There is also a different way to join up points that lie on a straight edge. Select the first point on the edge. Then holding down the "Shift" key and using the Marquee Selection tool select all of the points on the straight edge you wish to merge. Then simply pick Join from the Object menu. Thanks to Charles Blaquiere for suggesting that one.

Again this type of profile may be used to create an extruded object. Just extrude it to greater than the required length. Then add two planes where you want the ends of the object to be. Slice the extruded object with the two planes. Delete all the unwanted bits and join the body and two end caps. Of course, the slicing can be a problem. The preferred method that I use is to manually face the profile then extrude, but only with one section.


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© Richard Jennings 1997, 1998