# The plane truth

There are two basic kinds of objects in POV-Ray: objects that have a definite end, and objects that go on forever. POV-Ray calls these finite objects and infinite objects. A sphere is a finite object. A plane is an infinite one. Let’s add a plane to our scene.

//it's Magrathea!

plane {

y, 0

pigment {

color Gold

}

}

Render this one and you’ve got half of a sphere protruding from a golden plane. A plane goes on forever in two directions. This plane goes on forever left and right, and forward and back. You specify which directions it goes on forever by telling POV-Ray which direction it does not go on forever.

Rather than using left, right, up, down, forward, and back, POV-Ray uses x, y, and z as its directions. What we’ve been calling left and right is ‘x’. What we’ve been calling up and down is ‘y’, and what we’ve been calling forward and back is ‘z’. From now on, we’re going to use x, y, and z as well. Left, right, up, down, forward, and back don’t make much sense when we start moving the camera around.

The center of the universe is zero x, zero y, and zero z.

When we tell POV that our plane is “y, 0”, we are saying that the y axis is perpendicular to the plane. And the plane is zero units away from y’s origin (or, zero units away from zero y).

Where planes go on to infinity in two directions, they are infinitely thin in the other direction. Temporarily change your camera’s location from a y of 2, to a y of 0:

//camera is at eye-level

camera {

location <0, 0, -10>

look_at <0, 0, 0>

}

The plane disappears completely! All you can see now is the shadow that it casts on the lower half of the sphere. This is because the plane is infinitely thin, and we are looking at the plane straight on. If we were even slightly above it or slightly below it, we would see the plane, but we’re not. Go ahead and try a ‘y’ location of .0001 or -.0001 for the camera and see what happens. In both cases, you’ll seen the plane and either the top or bottom half of the sphere.

Before going further, restore the camera’s y to 2 and re-render it to make sure it is still half of a blue sphere on a gold plane.