Subdivision Surface Modeling

Subdivision surfaces combine all the good features of NURBS and polygonal surfaces; they allow organic shapes to be modeled easily and define perfectly smooth shapes with a varying surface.

Realsoft 3D provides a very powerful set of tools for modeling with subdivision surfaces.

This tutorial goes through a number of basic modeling examples for beginners.

Creating a coffee cup

The SDS toolbar allows you to create basic subdivision surface objects.

SDS tool bar

Click the SDS/Cube tool button. As usual, the control bar now shows you a number of subdivision cube specific options.

The options for the subdivision surface cube tool

Now switch to the top view either by clicking the top view button in the view control bar at the right side of the view winsow or from the view's popup menu Camera/Top. Define the cube through the view window by entering two points with the mouse. While doing this, you may hold down the Shift key in order to achieve a symmetric cube. A subdivision cube is created.

A subdivision surface defined by a cube-like control polygon

As you can see, the created cube defines an object which doesn't look like a cube at all. In fact, the cube tool created an object, which more or less looks like a sphere!

However, it is relatively easy to turn this spherical object to a coffee cup, or whatever other shape, as we will see soon.

This is actually a very common situation when modeling with subdivision surfaces. One starts from a very simple object, such as a cube, and adds details to it using different subdivision modeling tools.

The new subdivision object should be automatically selected after its creation. If you accidentallyy deselected it, click its name in the select window. As usual, the tool control bar automatically shows you the appropriate subdivision modeling tools as soon as a subdivision object becomes selected.

The control bar shows you the tools, which can be applied to the selected subdivision object

As you can see, most of the tools are disabled. The reason for this is that most of the subdivision modeling tools can only be applied in the 'Edit' mode. Subdivision objects provide three kinds of editing handles: faces, edges and points.

Select Face edit mode

Point handles allow you to single point edit the subdivision object. There are also a number of tools, which can be applied to points. There are also edge and face handles available - they modify several points at a time.

In order to turn our cube into a cup, we will be using the face handle mode. Select Face from the Control Bar's Edit field.

Select the top face by clicking it with the left mouse button. The selected face is highlighted.

Rotate the view window (drag downwards with the right mouse button Alt key held down) so that you can see the object's front and top sides. You can see a so called face normal handle sticking out from the selected top face. The face normal handle is perpendicular to the selected face and allows you to move the selected face.

Top face selected
Top face moved along its normal

Let's move the face to make our 'sphere' a bit higher. To do this, simply move the mouse over the center of the face normal handle and drag it. Note: don't drag the end points of the handle. They scale and rotate the face.

When you selected the top face, many of the subdivision modeling tools in the control bar were enabled. This indicates that they can be applied to the selected face.

Activate the Subdiv tool (Subdivide Face) and LMB click in the view window.

Subdivide Face tool

When you now move the mouse up/down, you can see the effect of the subdivision tool. When an appropriate subdivision degree is achieved, click the left mouse button again to accept the operation.

Top face subdivided
Top face extruded inwards

Now activate the Extrude tool and enter one point through the view window. By moving the mouse up/down you can extrude the top face up/down. If you extrude it downwards, the object starts to look like a cup.

The bottom of the cup is too round. Subdividing the bottom face adds new geometry, which will help to flatten the base. So, alt-drag with the right mouse button held down to rotate the view so that you see the cup from below. Click the bottom face to select it. Instead of pressing the Subdiv tool button, let's use the object handles. Hold the Ctrl key down and LMB drag the outer end knob of the face handle line. A new face appears and changes its size while you move the mouse. Make the new face almost as large as the original bottom face and release the mouse.

Bottom face subdivided

As you noticed, many useful subdivision tools can be activated by dragging the handles while holding a suitable modifier key down. The extrude tool which was applied above can be activated by Ctrl-dragging the actual face handle line, not its end knob. The handles usually provide the fastest way to achieve a certain action, because the tool is available at the same place where your focus is.

Now our cup is able to stand stable which is one of the basic requirements for a decent cup.

As you can see, with just a dozen of control points, we can define a cup with a smooth surface.

Extruding the handle

Most coffee cups have a handle. Let's see how we can use the Realsoft 3D modeling tools to create one.

There are numerous ways to create handles for the cup. Which one is the best method, depends on the case. For example, we can use the Extrude tool to extrude two "tentacles" out and connect the ends of the tentacles. Let's try this.

Click the Smooth tool. This subdivides the entire control polygon of the cup, producing a more dense control polygon. However, the actual shape of the cup is not changed by this operation.

Now, select two of the side faces (one on top of the other). Keep the Shift modifier pressed when selecting multiple faces.

Select two side faces and..
..apply the Subdivide Face tool

Now apply the Subdiv tool. Subdivide the selected faces just like we did when we subdivided the top face in the beginning of this example.

Activate the Extrude tool. When the tool is activated, the control bar shows you the available extrude tool specific options. Enter 3 into the Sections field in the control bar.

Extrude three cross sections

Now enter two points through the View window to get two tentacles extruded.

Two faces extruded with 3 sections
Extruded tentacles bent

Use the Realsoft 3D Bend tool (in the Transformation toolbar tab) to give the desired shape to the handle tentacles. To do this, rotate the view until you see the tentacles directly from the side. In the view window, LMB-drag a selection box, which includes the faces of the upper tentacle. The faces inside the box become selected. In edit mode, transformations modify only selected handles, and we can now bend only the upper tentacle.

Click the bend tool to activate it. Click once in the middle of the first cross section of the tentacle and click another time at the end of the tentacle. Move the mouse to find a suitable bend and click to finish the tool. Drag-select the bottom tentacle area and bend it, too.

Now we only need to connect the ends of the tentacles to finish the cup. To do this, zoom and rotate the view window to see the end face of the upper tentacle from below. Click to select it. Rotate the view upwards to see the end of the lower tentacle well. Press the Shift key (=multi select modifier) down and click the end face of the lower tentacle. When both faces are selected, the Tunnel tool in the toolbar becomes enabled. Click it to connect the selected faces. The cup is now ready.

The Tunnel tool

Tentacles connected