5.5.1. Cutting away "Extruded" shapes

Step 1

A quick and simple tool to remove unwanted parts of the model is to use the "Cookie Cutter" or "Extrusion" tool. This tool allows you to define a 2D curved or polygonal shape in the View Model Window and perspectively "back-project" it (i.e. "extrude") to create a 3D region. You then define the extents of the extruded region (i.e. how close the near and far planes lie) and then you can subtract (or add) the extruded shape to the current geometry (known as a "Boolean" operation).

The first step is to rotate the model until you are looking "front on" to a region that needs to be removed. You can use the View Dependent Textures button to help — this display mode gives some indication of how the final model will look when textured. Also select the Use Light Source button to see the shading from the current surface geometry.

Select the Orthographic mode button to display an orthographic view which will mean back-projected shapes are true "extrusions" with no perspective foreshortening. This is useful to extrude a "true" cube or prism. In perspective mode the back-projection is actually a section of a cone.

Step 2

The next step is to define a 2D curve. Select the Define region to edit button. A toolbar containing region specific tools is popped-up.

Now start to define your 2D shape in the View Model Window. Click with the mouse on the shape starting point. Continue to click on points around your curved shape or hold CTRL and click to insert a non-smooth polygon corner.

Close the curve by clicking the first point. Whilst outlining your shape you can use the undo (CTRL Z) and redo (CTRL Y) functions to go back and forward.

You can have multiple closed curves for more complicated 2D shapes which contain holes or several disjoint regions as shown below...

Select the "Fit plane" option to get 3DSOM Pro to fit a plane to the existing surface inside the region. The cutter will then be oriented so that the near and far planes are parallel to the fitted plane. This option can be useful if you were unable to orient the model to get a good "front-on" view.

Step 3

Click the Extrude selected shape button to extrude your 2D shape. A dialog will be displayed. And the initial extruded region will be displayed as a "cookie cutter" overlaid in the View Model Window.

To adjust the back plane of your "cutter" drag the slider back and forth.

If you wish to adjust the front plane of your "cutter" temporarily select the "Add Back" checkbox and adjust the slider position. Then uncheck the box.

To turn your "cutter" region into an extruded shape that will be added into the geometry (as opposed to subtracted from the geometry) check the "Add Back" checkbox.

To preview the current operation select the "Preview" checkbox.

You can change the 3D viewpoint at any time by selecting the Rotate (or Spin) model button or any of the other viewpoint tools.

Hit OK button when you are happy and the geometry is updated. The Boolean operation may introduce sharp edges (faceting) that need smoothing — use the Smoothing tool described below to handle this.

5.5.2. Smoothing or Flattening a surface patch

Step 1

Smoothing the surface within a region is very straight forward. Start by rotating the model to view the part of the surface that needs to be smoothed.

Step 2

Click the Define region to edit button and define a closed curve at the boundary of the region you wish to modify by clicking curve points or ctrl-clicking polygon vertices as for the "extrusion" tool described above.

TIP:	It is best to define a curve that is completely inside the model in the window. If your shape extends beyond the surface then the smoothing operation can result in parts of the model being removed.

Step 3

To remove bumps and "flatten" the surface within the region click Flatten region button — the surface will be immediately updated.

To smooth instead, click the Smooth region button — the following dialog will be displayed.

Step 4

Drag the slider right to increase the amount of smoothing or left to reduce the smoothing.

Select the "Preview" checkbox to see the effect on the geometry. You can see the mesh being updated and a progress bar is displayed in the status bar.

Step 5

When happy click OK button or Cancel button to cancel the smoothing operation.

5.5.3. Hollowing out using the "Push-Pull" tools

Step 1

You can push the surface inwards to create an indentaion within a defined patch on the surface. Similarly you can pull the surface out to create a bump within the defined patch.

Note:

To hollow out an object such as a vase, you will need to rotate the object in the View Model Window until you are looking straight down into the hollow region (i.e. top-down view of the vase). Then select the 2D shape of the neck of the vase and use the "Push-Pull" tool to push the surface inwards until it is hollowed out.

Step 2

Once you have rotated the object to the desired view, select the Define region to edit button and define a closed curve at the boundary of the region you wish to modify by clicking curve points or ctrl-clicking polygon vertices as for the "extrusion" tool described above.

Step 3

Now select the Push-Pull mode button. Place an "anchor" point by clicking in the centre of your 2D region.

Step 4

Now start to push the "anchor" point inwards by clicking and holding the Push Surface button. The anchor point will be displayed as a red sphere and the desired end-position is displayed as a green sphere. You can use the viewpoint tools to see how far back the green end-position lies (viewed from the side).

The surface will automatically start updating until the final "rest" position is reached. You can then add more anchor points by selecting the Push-Pull mode button again and clicking on the model. Repeat the process until the object has been hollowed out or the desired indentation has been created.

Use the Pull Surface button button instead to pull the surface outwards. As usual you can use undo CTRL Z and redo CTRL Y to undo or redo the positioning of your anchor points.

Step 5

When you are happy press the button to finish with the defined outline.