StageTools - Documentation (CenterStage/Tutorial)

## Combining Objects

You've just seen how to create an individual object, so now let's put several objects together into one scene.1 First, delete the surface you have been working with using the `Object/Delete` menu. Next, create a `Group` object by selecting `Object/New` and selecting the `Group` type in the selection list. After hitting `OK`, you should see the group object appear in the object list, but the definition window will remain blank. That's because a group doesn't have any values that you need to set; you can still enter things like sliders and other definitions that are to be shared by the members of the group.

To add an object into the group, select `Add` from the `Object` menu. For this demonstration, add a `Surface` to your group and make its functio be

```    Function {x y} {let z = x^2 - y^2}
```
Choose `Add` again and create an `Axes` object. Now press `Update` to see the compound object consisting of the surface and axes together.

Now we will add a third object, this time another `Surface`, and name it `Plane`; we are going to make this be a slicing plane that will cut the other surface. We'll make the slice be at a height h given by a slider. To do this, enter the following script for `Plane`:

```   Domain {{-1 1 1} {-1 1 1}}; # this makes a single square
Function {x y} {let z = h}; # every point is at height `h'
Slider h -1 1 0;            # the height for the plane
```
Now when you press `Update`, a horizontal plane should appear. Select `Solid/Blue` in the `Color` menu to make it blue. When you move the slider, the plane will move and cut the surface at different locations.

 1 In `Geomview`, each object that it displays is a distinct element that can be rotated, scaled and translated independent of every other. Indeed, as already mentioned, `Geomview` will scale and center the objects that you create, so two separate objects are unlikely to have the proper relation to each other in terms of their sizes and positions. Luckily, `Geomview` also has the concept of a hierarchical object; i.e., a single object made up from several pieces. These are handled in `CenerStage` by `Group` objects, which act as containers for other objects. All the objects in a group are treated as a single geometry by `Geomview`, and so the relative scaling and positioning are preserved between these objects.

 StageTools Documentation web pages Created: 08 Sep 2001 Last modified: 08 Sep 2001 23:35:56 Comments to: `dpvc@union.edu`