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SECTION 3: EXERCISE - CAR WING
(Point Cage Method)

This section is an exercise in using the Point Cage Method and follows the steps that are needed to create a simple car wing like the one mentioned at the beginning of this tutorial (but without the thickening of the metal nor the rim round the edge). It covers projecting a spline on to a curved 3d surface, creating polygons manually in a Polygon Object, moving individual points to follow the curve of an eliptical object, using two view in the Viewport stacked above eachother, using the Knife Tool and shaping the remainder of the object.

Create a sphere in Top View. Don't move it. Make it Editable and use the Scale Active Element Tool to make it wider, as in the image (which shows it at a later stage). Create a Linear Spline (Main Menu Bar > Objects > Create Spline > Linear Spline) as shown in the image (the Spline with all its Points selected) with its left end slightly to the right of the left end of the Sphere, and the right end of the Spline about three quarters along towards the right end of the Sphere, as in the image: Make the Points at the ends closer together as the curve of the Sphere Object gets steeper. (This is to make sure that there are enough segments to follow the Sphere surface closely.) Copy this Spline - the copy will appear in the Object Manager as Spline. 2

Change to Perspective View. With the Points Tool chosen and with Spline selected in the Object Manager, choose Main Menu Bar > Selection > Select all and Main Menu Bar > Structure > Spline > Project. In the dialogue box that appears, choose XY plane and press OK. As in the image, the Spline Object will be moved and wrapped around the Sphere. (If you made the Spline Object too long, the end Points will not Project.) This is a useful method (not only with HyperNURBS) for making the edge of an object, or a Swept or Lofted Spline, follow the contours of an object, as we shall see.

In the next steps we will be using the Structure Manager (Main Menu Bar > Window > Structure Manager). You need to know that there is a difference between choosing something from Main Menu Bar > Structure > xxxx, and choosing something from Structure Manager > xxxx. Keep the Structure Manager open somewhere on your screen, and choose Structure Manager > Mode > Points. Therefore, whenever an (Editable) Object is selected in the Object Manager, its Points data will be automatically displayed in a table. If any of that Object's Points have been selected, their data will appear in the table in a different colour.

The next step is to get all the Points of both Splines into a Polygon Object. Create a Polygon Object (Main Menu Bar > Objects > Polygon Object). Its Structure Manager (which will be open following the advice above) will be empty because it does not contain any Points. Select Spline in the Object Manager and select all its Points - (Choose the Points Tool, then Main Menu Bar > Selection > Select All). Spline's Structure Manager being open, Choose Edit > Copy. (All the data on Spline's Points will change colour.) Select the Polygon Object in the Object Manager, and in its Structure Manager choose Edit > Paste. The Structure Manager will fill with a table giving information about each of Spline's Points. Select Spline. 1 in the Object Manager and repeat the above operations, resulting in a second set of Points in the Polygon Object's Structure Manager. Remember not to use the Copy and Paste operations available from the Main Menu Bar > Selection.

In Top View, select the Polygon Object in the Object Manager and do Main Menu Bar > Selection > Select All to see its points looking the same as when you looked at both the Spline's Points. Deselect them. Now we will create Polygons. With the Polygon Object still selected in the Object Manager, choose the Points Tool and the Bridge Tool (Main Menu Bar > Structure > Bridge, shortcut B). The mouse pointer will change to a shape like a bridge. Click on the bottom left Point and drag upwards to the corresponding Point directly above it. Repeat for each of the pairs of Points as Polygons are created. The image shows one new Polygon about to be created (although the screenshot does not show the bridge-shaped mouse pointer.) Change temporarily to Perspective View to check.

It is important to create these Polygons in one operation. That is, without doing anything else part-way through. If you do, restart using the Bridge Tool by Bridging again the last pair of Points.

The next step is to start curving the top surface of this Polygon Object. In preparation for this, in Top View, use the Knife Tool to create an Edge as shown here (called the "Top Ridge Edge"): To do that, change the Viewport to two Panels (Viewport Menu > View > 2 Views Stacked) as shown in the next image, setting the Top Panel to Front View and the Bottom Panel to Top View: Drag the horizontal divider between the two views down a little to make room later for the Y-axis arrows in the Top View Panel. Create a Primitive Spline (Main Menu Bar > Objects > Spline Primitive > Circle). Drag it down in the Top View Panel so that in 3D space it is in front of the Sphere and therefore visible in the Front View Panel (you might need to change temporarily to a single View Panel). In the Front View Panel scale and position it as shown. This is to represent the wheel (with a greater diameter to allow for space under the wing).

We will now raise the front edge of the wing (that is, the row of Points at the bottom of the Top View Panel as in this image): To do that, in the Top View Panel, select the second left Point of the bottom row of Points. In the Front View Panel, move that point up a little. Select and move all the other points one after the other, as in the image, moving the Mouse Pointer from one Panel to the other for each Point: The image shows a selected Point in both the Front and Top View Panels after having been raised a little.

Next, do the same for the Points on the "Top Ridge Edge", raising them above the "wheel" circle. To see the smoothed result, create a HyperNURBS Object and drag the Polygon Object on to it in the Object Manager so that the Polygon Object becomes its Child. Change to a single View Panel, Perspective view, to see the result:

So now you know how to attach a wing to an egg before it is hatched!