Cinema 4D / BodyPaint 3D Program Documentation Tutorials Mechanical Modeling Tutorial Subdivision Surfaces Modeling
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Modifying a Subdivision Surfaces shape

As demonstrated with the Spline objects above, a Subdivision Surfaces object smooths longer, flowing edges. Sharper edges, however, leave less space for an edge to be rounded, resulting in a fairly sharp corner. Additionally, areas with greater subdivision will have an even higher subdivision after a Subdivision Surfaces is applied than areas with relatively long curves. In the following we will demonstrate how this can affect your workflow:

Create a Polygon object (Create| Object | Primitives | Polygon). A four-sided polygon will appear in your Viewport. Next, create a Subdivision Surfaces object (Create | Generators | Subdivision Surfaces). In the Object Manager, make the Polygon Object a child of the Subdivision Surfaces. The Polygon object will automatically be subdivided according to the Subdivision Surfaces default Subdivision value.

Left the original Polygon object, right the same object after being smoothed by the Subdivision Surfaces.

The Subdivision Surfaces only subdivides the top-most Child object in its hierarchy. However, by making subsequent objects a Child object of the first Child object, these will be subdivided by the Subdivision Surfaces as well. A good method for doing this is to use a Null (Create| Object | Null Object) as the top-most Child object and making all other objects you want affected by the Subdivision Surfaces a child of the Null Object (when the polygons are made Child objects of the Subdivision Surfaces object, the resulting object’s size will be reduced).

Display types

Now that a Polygon Object has been made a Child object of a Subdivision Surfaces we are, in principle, now dealing with two objects. This means that you can choose which shape with which to work when making modifications. You can either modify the original polygonal object’s points, edges and polygons, or you can use Isolines, i.e., the smoothed structure, to modify the object. In the image below, both methods of modification are shown.

You can define the mode in which you prefer to work in the Viewport’s Configure... settings. The viewport configuration options will be displayed in the Attributes Manager, in which you can enable or disable the Isoline Editing option. Regardless of the mode used, the Polygon Object, and not the Subdivision Surfaces, must be selected to make modifications.

Subdividing multiple objects

When subdividing multiple objects assigned to a single Subdivision Surfaces, the ability to assign individual Subdivision values can be very practical. After all, not every object requires the same amount of subdivision. A special Cinema 4D tag has been created for this purpose. This tag can be applied by right-clicking on an object in the Object Manager and selecting Cinema 4D Tags / Subdivision Surfaces Weight from the menu that appears. This tag can then be used to assign individual variances to the defined subdivision value - even a value of 0 can be entered, which will result in the Subdivision Surfaces Subdivision value being completely ignored for that particular object. In the following section about Subdivision Surfaces weighting we will go into more detail about this tag.

Subdivision Surfaces weighting

In addition defining the Subdivision Surfaces shape via its Child object’s polygons, weighting in the form of Subdivision Surfaces Weights can be used to further influence the Subdivision Surfaces shape in specific points or edges. This weighting can be applied separately to points or edges. Even polygons can be weighted, which however requires all points and edges of that polygon to be weighted.

Weighting can be assigned by selecting points, edges or surfaces, and click + . + dragging the mouse (Make sure the object is made editable before doing so - otherwise you will not be able to select any points, edges or polygons).

To assign/vary weighting for our example object, make it editable by selecting it and pressing the c key on your keyboard (alternatively you can select the Make Editable from the Mesh | Conversion menu). Next, switch to Points mode, select a point and add weighting to it, as described above. You can adjust the point’s weighting to a value between 0% and 100%. Click + . + dragging on a point, edge or polygon will automatically add a Subdivision Surfaces Weight tag. This tag contains all weighting information for a given object. Selecting the tag itself will display the weighting as a color gradient on the object, as shown in the image below. If you want to remove all weighting from an object simply select its Subdivision Surfaces Weight tag in the Object Manager and delete it.

Defining weighting numerically

The weighting effect can be defined even more accurately by selecting the Live Selection and switching to its Subdivision Surfaces tab in the Attribute Manager. This tab’s settings can be used to very accurately adjust an object’s weighting. For example, the Mode option can be used to "set”, "add”, or "sub”(tract) the defined Strength value. Click on the Set button each time to apply the Strength value.

The Interactive Minimum and Interactive Maximum values define the weighting range that is applied when click + . + drag is used to assign/vary weighting. The green color in the image below reflects the negative weighting.

In order to better demonstrate what Subdivision Surfaces weighting can do we will add an extrude to our Polygon Object. Switch to Polygons mode, select the Polygon object’s surface and activate the Extrude tool (Mesh | Create Tools). In the Attribute Manager, activate theCreate Caps option (this will ensure that the original surface is maintained after being extruded, thus creating a voluminous body). Extrude the surface by either clicking and dragging in the Viewport or by manually changing the Offset value. Extrude the surface until it looks like the object at the left of the image below. Remove the object’s Subdivision Surfaces Weight tag so we can proceed with an "unweighted” object. In the image below, examples of different weighting are shown in the center and at the right. The center object’s entire surface was assigned a weighting of 100%, which resulted in the Subdivision Surfaces assuming the shape of the Polygon object in the area of the surface. On the object at the right, only the four edges of the top surface were weighted, and the corner points were not weighted. This resulted in a circular-shaped surface being formed.

As you can see in the image below, pillow-shaped or cloth-shaped objects can be quite easily created. The shape at the left is a result of the four vertical edges. The shape at center shows what can result when the top four corner points are weighted as well.

As practical as Subdivision Surfaces weighting can be, it bears one major disadvantage: Weighting does not increase the subdivision at the weighted areas. This can easily result in undesired jagged shapes. These jagged shapes can be avoided with the help of increased Subdivision Surfaces subdivisions, which will also increase the number of polygons for the entire object - sometimes dramatically. The shape at the right of the image above illustrates how an increase in subdivision does not occur in weighted areas (in this case around the four lower points that were weighted to 100%). The amount of Subdivision Surfaces subdivision is always constant and in relation to the number of edges of the object to which it is assigned.

Solid chamfering

As we already know, increasing weighting will not increase Subdivision Surfaces subdivision locally. To increase subdivision locally, subdivided regions must be added. This is called solid chamfering. When applied correctly, a Subdivision Surfaces child object can be modified locally to give it a look ranging from softly rounded to sharp-edged. This is illustrated in the image below. In the top example, a vertical edge of the bounding box was split using the Bevel command (Mesh | Create Tools) (Bevel Modemode

Chamfer). The result is an increase in the number of points and edges in that region of the bounding box that in turn increases the effect of the Subdivision Surfaces in that region. We could have achieved a similar result by weighting the original edge but we could not have created the additional subdivision that makes the final shape so perfectly rounded.

Even individual points can be chamfered using the Bevel command. This is illustrated by the center object in the image above. As you can see, the result is a tapered shape at the beveled point. The shape at the bottom of the image below illustrates the result of applying a bevel to an entire quadrangle. This generally requires the use of the Loop/Path Cut tool (Mesh | Create Tools) in Loop mode. A relatively sharp edge can be achieved depending on the distance between the location of the cut and the nearest edge.

Using solid chamfering

Let’s continue with the example from above. Scale the quadrangle’s top caps surface down using the Extrude Inner command (Mesh | Create Tools menu). A further extrusion can be used to create a dome-shaped "nose”, as shown in the image below. In this case you have to make sure that the Caps option is disabled before extruding to prevent hard transitions from being created.

If you also wanted to sharpen the object’s left and right edge some more you would have to add a cut line, as described above. This is also illustrated in the image below on the right. This however would create triangles that would disrupt the smooth surfaces of the Subdivision Surfaces subdivision. As you can see, solid chamfering can deliver better results than weighting, but it also requires careful planning in the modeling phase. In order to solve the problem of sharpening the edges we must first undo the extrusion of the dome shape. The sides can then be cut using the Loop/Path Cut tool without creating triangles. At the left of the image below the additional edges can be seen. Subsequently the Extrude Inner and Extrude tools can be used to again create the dome-shaped "nose”.

Cuts for creating additional edges should generally be made in the direction of Polygon Loops. This will automatically result in quadrangles being generated. The disadvantage lies therein that new points and edges, which should not necessarily be affected by the Subdivision Surfaces, will also be created in these regions. To prevent this from occurring, edges should be repositioned in order to reflect the original Subdivision Surfaces shape as closely as possible. This is illustrated at the top half of the image below. Two horizontal cuts were made near the top and bottom cap surfaces in order to sharpen the left-hand edges. The rounded edges at the right were maintained. As you can see, all that needs to be done to give the Subdivision Surfaces more room for creating a smooth rounding is to increase the distance between the edges of this cut.

In the bottom half of the below image, arrows illustrate additional cuts that can be made to sharpen the radii of the extruded "nose”.

Further steps that are required to square off the "nose” and additional sides of the base are illustrated below. A total of four additional cuts must be made to compensate for the stronger weighting of the edges. This is done best using the Plane Cut tool’s Plane

XY and YZ mode.

As you can see with the image at the far right, with a little planning in the modeling phase, even protruding edges can be created using this technique! Key for the Subdivision Surfaces is always the distance between edges. The closer that edges lie to one another the sharp the resulting edges.