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A Coke (TM) Can

             A Coke (TM) Can

The Detail Editor has a powerful tool called sweep that can create simple radially symmetric objects like a soda can or a candlestick holder. However, the Forms editor can one-up sweep pretty easily.

Our goal is to create an object in the shape of a standard 12 ounce soda can with all the details like the hollow on the bottom and the little metal ridge on the top. The Forms Editor can create objects like this with no trouble, and do it faster and much easier than using the Detail Editor to spin a line outline of the can would take.

Enter the Form Editor, and make a new form (in the Object menu) with 4 slices and 20 points. A can at first approximation is just a cylinder. We need many points around the radius to get a nice smooth circle cross-section, but only a few slices to define the rectangular vertical cross-section. For this example, we'll never muck with the 20-point circle cross section.

The cylinder is obviously radially symmetric, so we will probably want to turn on 90-degree symmetry from the symmetry pull-down menu. The points that you manipulate in the front and right views will now move their corresponding siblings, keeping the object radially symmetric.

To make a quick and dirty cylinder, move each point in the vertical cross sections so that they are on the same Z line- they should stack vertically on top of each other. I like manipulating the right hand cross section in the Front view. Remember, the symmetry mode will move the other three points for you. You can use the perspective view to see what effect you're having on the form. You might look at the screen-grab called can_one to see how the first simple model should look. Again, these screen-grabs have to be downloaded from the FTP site hubcap.clemson.edu.

What do we get? Well, our horizontal cross section is unchanged, its still a nice circle. We don't want to muck with it. Our horizontal cross section is a nice straight vertical line. If you think about it, this should give us an object in the form of a tube. If you look at your perspective view and don't see a tube, something is wrong. Look at the can_one picture again to see what the problem is.

There are two problems with this tube. First, the sides are a bit wavy, since each point was moved manually and they might not be exactly on the same vertical line. Second, if we really want to make a Coke can, we should at least get the proportions and scale right so we don't have to squash and stretch things later to get it to look reasonable.

To fix the wavy line problem, we just use "lock" mode from the select menu. Remember, this will make any point we move jump to grid intersections, so if we move the points around by the same Z line they'll all line up on the same grid line.

We should also figure out how to get the right can proportions. If you get out a ruler, you'll find a standard Coke can is 12.2 cm tall and the main body is 3.25 cm in radius. It is difficult to accurately change the radius of our form, but we can make every other measurement use the default radius of 100 Imagine Units as a reference. Hence, there are 3.25 cm in 100 Imagine Units, so the can should be 375 units high. If we change the grid spacing to 25, our can should be fifteen grids high. It is easy to automatically set the height of our object, because the points will leap to the right position when we move them to the correct (coarse) point. You might want to turn on "coordinate" mode from the display menu to help identify where you are moving your points.

It might occur to you that we also don't want a tube, we want a solid cylinder, with ends. This is easy to make, we'll just take the top cross section point and move it to the Z axis to enclose the top and move the bottom point to the Z axis to enclose the bottom. This gives us the rectangular cross-section we need to form a cylinder.

We'll make our can so that the axis is at the very bottom, at 0, 0, 0, and the can rises to a height of 375 in the Z direction.

To actually change our rough tube to this properly proportioned, capped cylinder, set the grid size to 25, turn on lock, and move the top right point in the FRONT view to the 0, 0, 375 grid intersection. The other views should show the corresponding points moving up as well. Move the second point to form the outside top edge of the can, to 100, 0, 375. The third point forms the side, at 100, 0, 0, and the last point will define the bottom, and should go to 0, 0, 0.

Your can should look like the picture can_two.

Ok, this DOES indeed look like a nice cylinder. So how do we get the nice details like the top rim, and the dent on the bottom, and the narrower "lip ridge" just below the top rim? I said that it was easy to add detail once you had a basic, crude form. Let's make the bottom dent of the can. Turn _off_ lock, so that we can move the points freely to whatever location we want. We want to add come points to the vertical cross sections so we have more control over the shape of the can.

Select 'Add' from the mode menu. Now, whenever you click on a point, a new point will appear at the midpoint of the line below it. We want to add a point to the very bottom line segment (Which is currently the horizontal line making the bottom of the can). Just click on the bottom outer point and a new point should appear on the bottom horizontal line. Enter 'Edit' mode from the mode menu, and you'll find this new point is just as easy to manipulate as the originals.

To form the bottom dent, we want to move the very last point on our Z centerline UP to make a cavity. The point should be moved about a third of a cm, or 10 units. You might want to turn on 'coordinates' from the display menu to help measure the distance. Once you move the point up, you'll see the dent in the perspective view if you move it so you can view the bottom of the can. The new point that we added can be moved up to make the bottom dent more bowl-like instead of a cone.

The trick to adding detail is to identify where you want to add a new feature. If you want to add a new dent or bulge, a new point added at the location you want can be moved in or out to make the feature. If you need to line things up, judicious use of changing the grid size and using 'lock' will let you place the points accurately. Note that the Forms editor LACKS the transformation requester that you find in the Detail Editor, so you can't just type in coordinates for critical points. You have to use grid size and lock to accurately place objects.

OK, we know how to add details. Now how do you take the measurements off of the can? There are a few ways- you could judge by eye, you could take a ruler and measure everything, or you can try sneaky tricks. If you fake it by eye, your model is obviously going to be somewhat inaccurate, even if you use a can sitting right next to you as a model. Measuring distances works quite well, though. I used a finely measured rule and a sheet of graph paper to transcribe the shape of all the ridges and bumps. Inputting these coordinates to Imagine involves using the Coordinates display and matching points.

However, there is a quick and dirty trick you can use, though this probably isn't applicable to most objects you model. Zoom the front view so that it takes up the whole screen. Center your can in your display by using the "set center" command in the Display menu and clicking at the center of your object. Now, zoom in or out until the size of the outline on your monitor approximates the real size of a Coke can. Take a real can, and press it against your monitor, then eye it. Use the radius as the determining factor, not the height. Now repeatedly use the "set zoom" command from the display menu and muck with the zoom to get the screen can size as close as you can to the real can size when you press it against the monitor. On my 1950 monitor a zoom of 1.05 worked well, but it will vary from monitor to monitor.

Once you match sizes, you can actually press the can against the screen with one hand, and move points to match the can outline with the other. [You'll look like a fool if anyone else is around, too!] However silly this seems, I found it the easiest way to input the shape of the can. When I sat with a ruler and some graph paper, my paper diagram turned out to be less accurate as the screen method and took much more time.

A rehash on adding the fine details: You have a rough outline. To refine it, just pick the area you want to refine, add a new point on that line, and drag it where you want it. I found that getting a highly accurate cross-section (using 17 points) took less than 3 minutes with the admittedly stupid screen trick. Using a ruler I spent 10 minutes measuring and converting before I even moved the mouse.

When you're done, you should have an outline similar to mine, which is shown in the picture can_three.

Take a look at your object in the perspective mode with the window zoomed to full screen, and solid display mode on. Rotate the view up and down. Nice, huh?

What about the top hole, and the tab? The tab is easy to add in the Detail Editor, by extruding a flat outline. If you expected to make it as an integral part of the can form, I'm sorry to say you were expecting a bit much. The Form Editor likes to make single-piece objects, and you can see how the tab is really a separate part of the can "form." This doesn't prevent you from making a separate tab object and sticking it on, and this is exactly what I did.

The hole, on the other hand, is pretty easy to include using the Form Editor! If the hole is facing towards us as if we were going to take a drink, the hole is obviously non-radially symmetric, and it is not front-back symmetric. It IS left-right symmetric. Turn the symmetry from the radial '90-degree' to 'right'. Now, in the FRONT view, move the top point (that is now on the Z axis) straight OUT about a third of the way to the outer radius. This is the WIDTH of the hole on top.

In the RIGHT view, move the left-top point (which is the front-top on the can) about 90% of the way to the can rim. Leave the right-top point where it is. The finished can form can be seen in picture can_four.

See what we've done? Moving the points away from the center made a hole. We made the front-to-back cross section asymmetric to one side, so the hole location is moved. Look in the perspective view. Play around with moving the hole around and turning symmetry on and off.

Why did this make the asymmetric hole? Remember how the form is generated? Each cross-section is interpolated from the 4 defined cross sections. The front cross section blends to the right, which then blends to the back, then to the left, then back to the front. This is very hard to describe, but play with the points and you'll see the kind of control you have.

Note that the hole is an oval, which is not quite true for a can. The Forms editor really won't let you do much more unless you want to start mucking with radius modulation, but that's for the next example.

This completed can object can object can be loaded into the Detail editor, at which point it becomes a normal object. You can move individual points, apply brush maps, attributes, textures, and manipulate it in any way you would a normal object. After manipulation in the Detail Editor, the objects are generally not reloadable back into the to the Forms editor. Using the Detail editor, you might make and attach the can tab, or move individual points on the top hole to make the ellipse to match a real can's hole more accurately.

A final rendered view of a can generated using this tutorial can be seen in the HAM image 'Craftsman', where you can see two separate versions of the can. The carved wood Coke logo was an experiment that turned out well. The Coke logo itself was made with wire cutters, a real can, Digiview, and an hour's touchup in DPaint III.

The can could have also been generated in the Detail editor by using the powerful "Sweep" mold function. However, sweep certainly does not provide the interactive updates that the Forms Editor does, and can only make completely symmetric objects. The next examples will show how much more powerful the Form Editor is when it makes very non-lathed objects.

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