Solid of Revolution

 

In the real world we are surrounded by many (artificial) objects that show an axially symmetric shape, like bottles, wine glasses, vases, or columns. This property of an axially symmetric shape facilitates the 3D modelling in blender, since it provides a couple of tools for creating such kind of meshes. Actually, in order to create such an object we only need to draw a 2D outline segment and let the built-in tools of blender do the rest. And even for this step, we can use a helpful feature of blender: We can import a background image that serves as a drawing pattern.

The modelling of a mesh will be performed, as usual, in the EDIT MODE (use the TAB key to switch between the EDIT and the OBJECT MODE). First, we have to choose a certain 2D projection, or view on the scene. For the present example I used the orthographic front view as my modelling plane.

 

Excursion: You can easily switch between different views on the scene by the use of the keys of the number pad: In order to change from perspective to orthographic view (and vice versa), you will use the 5 on the number pad. The front view is enabled by the key „1“ (X-Z-plane), the top view by „7“ (Y-Z-plane), the side view by „3“ (X-Y-plane), and the current camera view is selected by the key „0“.

 

As already mentioned above, we want to use a background image that will help us to make a proper drawing of the outline segment of a wine glass. First, we have to check the option BACKGROUND IMAGES in the right menu bar (see Fig. 1 – 2) and load the respective image. After the image is loaded we can do some modifications on that image, for instance, change its size, its position in the plane of view, and even its transparency (note that such background images will not be taken into account when the scene is rendered). For our purposes, the background image should be placed in the horizontal center of the scene, i.e., the vertical middle axis of the glass that is displayed in the image should coincide with the height axes (= Z-axis) of the scene (see Fig. 1 – 3).

 

Figure 1.

 

Now, we want to reconstruct the displayed glass in blender, namely as a 3D object. The very first thing we need is a single vertex, or maybe a line. We will receive a single vertex by adding a plane to the scene (ADD MESH PLANE) and removing three of its four vertices in the EDIT MODE. The remaining vertex will be our starting point and it should also be placed at the center of the image, i.e., on the Z-axis (Fig. 1 – 3), which is the rotation center of our glass object. So, the x- as well as the y-position of that point should be 0.

We can now start drawing the outline segment of the glass object: We select our vertex and extrude it (hot key: E) in the EDIT MODE, i.e., we add a new vertex that is connected to our old one and place it at the next position of the outline segment. These two steps (extruding and positioning of each following vertex) will be repeated until we have drawn the entire contour (see Fig. 1). As you can see, we built the outside as well as the inside of the contour of the glass. The very last vertex of this line should be placed at the rotation center again (x- and y-position will be 0) which is the deepest point within the interior of the glass.

So far, we have already done the creative work on our glass object—the rest will be done by the use of some blender functions: First, we have to select the entire contour that we just built up (hot key: A). Second, we have to change our viewport to the orthographic top view (hot key: 7 on the number pad). In this viewport we will see our contour from above as a one-dimensional group of vertices, but it is necessary to choose this view to tell blender that we want to rotate this contour around the Z-axis.

So, let's start the rotation of our line segment: In the left menu bar (MESH TOOLS) we have to click on the option SPIN under the category ADD (Fig. 2 - 1). As default values we have 9 steps, or number of segments, respectively, and an angle of 90 degrees for the rotation sector, as you can see in the bottom of the left menu bar (see also Fig. 2 – 2). We have to change these values manually: For the number of segments I used the value 36 and for the rotation segment a complete revolution, i.e., 360 degrees.

Caution: At this point an error may occur: The resulting object may look very weird and distorted. If you experience such deformations of your object you should undo the last steps of the rotation process (CTRL + Z) and ensure that the center of your object (your line segment) is located at the Z-axis as well. If this is not the case you have to select the mesh in the OBJECT MODE, then you have to click the button MESH at the bottom menu bar, select the option TRANSFORM and click the option ORIGIN TO 3D CURSOR (which is assumed to be on the Z-axis—if not, just place the 3D cursor somewhere on the Z-axis by adjusting the values in the 3D CURSOR LOCATION option in the right menu bar).

 

Figure 2.

 

If everything went well so far, we have the shape of the complete object in front of us. However, we still need to do some modifications on that mesh: Our mesh contains some doubled vertices (i.e., vertices with identical coordinates), due to the rotation we applied to it before. In order to remove these vertices one has to select the entire mesh in the EDIT MODE (hot key: A), then press the button MESH at the bottom menu bar, select the option VERTICES and click the option REMOVE DOUBLES in the sub menu (see Fig. 3 – 2).

 

Figure 3.

 

So, let's have a look at the result (press F12, in order to render the scene). Usually, the result still looks a bit rough at this stage: In the present version our glass has a rather polygonal appearance and, of course, no material properties that may evoke the impression of a glassy object in the beholder. So, let's first smoothen our glass, which I will do in two steps: First, we will add a modifier to our mesh. Click the button MODIFIERS (the screw-wrench symbol in the menu bar at the very right ) then click the button ADD MODIFIER and select the option SUBDIVISION SURFACE. Using this tool, further vertices will be added automatically to our mesh that will be set at interpolated places of the global shape of the object. Second, we will give our object a smooth shading by use of the button SMOOTH in the left menu bar (OBJECT TOOLS). That's it: our glass object now has a perfectly round shape!

The last thing to do is give it realistic material appearance. We will switch to the MATERIAL section in the menu bar at the far right (click the button with the shiny sphere) and adjust some material settings. Unless you want to create a colored glass, the default settings of the diffuse component are already fine. The most important properties we have to add to our object in order to give it a glassy appearance are transparency and some mirror reflections: First check the box at the category TRANSPARENCY (Fig. 4 – 1), then select the option RAYTRACE. In order to determine the degree at which the light will pass through our object, one has to adjust the ALPHA value (the higher this value is the more opaque our object will be). I gave it an ALPHA value near zero, since I want to have an almost perfectly transparent glass. The next value we want to adjust is the IOR, i.e., the index of refraction. We all know that light is refracted when it passes from one medium with a certain optical density through another medium with a different optical density (for instance from air to water). Typical IORs for glass range from 1.46 (quartz glass) to 2.14. I choose the value 1.525 as the IOR for my glass, just feel free to try out further values and see how this changes the appearance. Additionally, I changed the value DEPTH in the transparency category from 2 (default) to 4, just to increase the maximum number of interreflections.

 

Figure 4.

 

Finally, I added some mirror reflections to my glass object: Check the box at the category MIRROR (Fig. 4 – 2) and adjust the REFLECTIVITY value in this section (the value 1 corresponds to a perfect mirror). I gave it a quite low value of 0.089, since higher values already caused an enormous degree of mirror reflection—at least to my sensible eyes.

Well, basically, we are already done with our object now. However, if you render the glass in its present incarnation, you might be somewhat disappointed, since it looks rather misty. Of course: The material properties we used for our wine glass (transparency and mirror reflections) will only come into play when there are further objects in the surrounding of our glass—objects that you can see through the glass, or that are mirrored at the surface of the glass, respectively. So, I simply added a cube which I used as a “room” and gave its “walls” a checkerboard texture. As lighting, I used a simple point light source and enabled ENVIRONMENT LIGHTING in the world settings. That's it!

 

 

© 2011 G. Wendt



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