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3ds Max : CrossSection Modifier


CrossSection Modifier

The modifier known as CrossSection is a powerful tool for creating a continuous "skin" across multiple 3D splines. By connecting the vertices of these splines, CrossSection can generate a new spline object that can be further manipulated using the Surface modifier to create a patch surface. These two modifiers are often collectively referred to as "Surface Tools."

One of the unique features of CrossSection is its ability to create skins across splines of varying shapes, vertex counts, and open/closed status. However, the more diverse the splines in terms of complexity, the greater the likelihood of discontinuity in the resulting skin.

It's worth noting that the Editable Spline object provides similar functionality to CrossSection. By using the Connect Copy and Cross Section tools at the Segment and Spline sub-object levels, users can create a spline cage and manually transform its vertices. This method also offers greater flexibility in defining the order of splines compared to CrossSection.

Discover the functionalities of the CrossSection modifier

Let's take a look at how to use the CrossSection modifier with the following steps:
  • Open the  Create panel and select  "Shapes." Choose "Circle" from the options.
  • In the Top viewport, drag the cursor to create a circle with a radius of around 100 units.
  • Select the "Edit Spline" option from the Modifier List in the Modify panel  
  • Turn on "Spline sub-object" in the modifier stack display and  select the circle.
  • In the Front viewport, use the Shift+Move command to copy the selected spline upwards.
  • Repeat step 5 to create a third circle. Note that the order in which you attach or clone splines is important as it determines the order CrossSection uses to create the skin.
  • From the Modifier List, select the "CrossSection" option on the  Modify panel.
    The CrossSection modifier will join the vertices of the three circles, producing a basic spline cylinder.
  • To transform the spline cylinder into a patch surface, add the "Surface" modifier from the Modifiers List in the Modify panel . Check Flip Normals if the cylinder appears black.
  • To edit the model's surface, use the controls in the Edit Spline modifier. Alternatively, since the output of the Surface modifier is a patch surface, add an "Edit Patch" modifier and use patch edit controls to change the surface.

Utilize the CrossSection modifier to envelop multiple splines with varying shapes.

Discover how to use the CrossSection modifier in your 3D modeling software to create a complex shape by skinning various splines with different shapes.
  • Begin by opening the 3D modeling software and accessing the  Create panel. Click on the  "Shapes" option to initiate the process.
  • Next, turn on "Start New Shape" on the Object Type rollout, then choose "NGon." In the Top viewport, create two five-sided circular NGons.
  • Click on the "Line" option from the  Create panel (while the  Shapes option is still active), and create two lines, each with four vertices. Ensure that you make the vertices in a left-to-right direction.
  • Use the  "Select and Move" tool from the main toolbar to move the objects in the viewport along the Z axis, with the NGons at the bottom and the lines above the NGons.
  • Select the bottom NGon and access the  Modify panel. Choose "Edit Spline" from the Modifier List, and then click on "Attach" in the Geometry rollout.
  • Select the remaining NGon and lines in an ascending order, as numbered in the image. Remember that the order of selection is crucial because the CrossSection modifier utilizes the selection order to define the skin.

  Arranging the Vertex Points:

  • Open the  Modify panel and select the Vertex sub-object level from the stack display. It is crucial to align the first vertex point of every spline to avoid any surface twisting.
  • To align the points, hold down the Ctrl key and click on the rightmost vertex point of each line and the bottommost vertex point of each NGon.
  • Next, navigate to the Geometry rollout and select Make First. This step is vital as the first vertex point is where the seam splits from a closed to an open spline.

Creating a "skinned" shape using CrossSection and Surface:

        To create a smooth and consistent surface for your shapes, you can use the CrossSection and                 Surface modifiers in 3D modeling software. Follow these steps to apply these modifiers:
  • Go to the Modify panel and select the CrossSection modifier from the Modifier List. This modifier connects the splines at the vertices of your shape.
  • Next, choose the Surface modifier from the Modifiers List. This modifier generates a patch surface based on the splines.
  • In the modifier stack display, select the CrossSection modifier.
  • Within the CrossSection Parameters rollout, toggle between Linear and Smooth to see how the splines change and adjust the modifier accordingly.
  • Now, toggle the Show End Result On/Off toggle on the Modify panel to view the final patch surface. Note that this toggle won't remain on if the CrossSection modifier is currently selected. If you want to keep the toggle on, drop down to the Editable Patch in the stack and turn on the  Show End Result toggle.
A helpful tip to keep in mind when using the CrossSection modifier is to draw your splines in a consistent direction. If you create lines from vertices that are not properly aligned, a twisted surface can result. Keep your splines aligned and your final shape will be smooth and consistent.