Exploring 3D space with a computer – an Introduction
Adrian Oldknow
Papery things
Clicking the arrow at the bottom right of the fourth icon opens up a menu of things which can be coloured in - which is what I meant by papery. As these have length and breadth but no depth, they are technically called two-dimensional - and we can think of them as pieces of paper or cloth. These surfaces are represented on the screen as regions, whose colour and style can be changed.
Can you identify the shapes and how they were made? See the effect of dragging points like Z or B' . Which of the shapes on the menu cannot be seen in this figure? As usual there is a Cabri 3D file for you to download and play wit: 
Papers.cg
So now you have met all the main `building blocks' from Cabri 3D from which we will create objects. One means of creation is the intersection of objects - which might produce a point (such as a line piercing a plane) or a curve (such as a plane slicing a sphere)
In this manipulative, the segment AB has been created in the ground-plane. The point C has been created to belong to AB . This is a key technique - where the movement of a point on or round an object controls the movement of other objects. We call a point like C a `slider'. The vertical vector OZ has been used to define a line which is perpendicular to the ground plane. The line OZ together with the point C are used to define a plane whose rotation about OZ is controlled by the slider C . Points D and E in the ground plane define a line DE . Point F is the intersection point of the line DE and the plane OZC . Drag C and view how F changes. The Cabri 3D file is called
Door.cg3
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