## Documentation Center |

Position of light sources relative to the camera?

Objects | CameraCoordinates Default Values |
---|---|

plot::DistantLight, plot::PointLight, plot::SpotLight | FALSE |

With `CameraCoordinates = FALSE`, the coordinates
defining the position of a light are interpreted as model coordinates
in 3 space. Thus, the lights are positioned relative to the objects
in the scene. They do not move when the camera moves.

With `CameraCoordinates = TRUE`, these coordinates
are interpreted as "camera coordinates". Thus, the lights
are attached to the camera and move automatically with the camera
when it is moved.

A vector (*x*, *y*, *z*) in
"camera coordinates" has to be interpreted as follows:

The *x*-coordinate
refers to the horizontal axis of the picture that you see in the finder
of the camera. Positive *x* values
are to your right hand side, negative *x* values
to your left hand side.

The *y*-coordinate
refers to the vertical axis of the picture that you see in the finder.
Positive *y* values
are above you, negative *y* values
below you.

The *z*-coordinate
refers to the position along the optical axis of the camera. Positive *z* values
refer to points in front of you, negative *z* values
to points behind you.

In camera coordinates, the camera position is (0, 0, 0).

For example, a point light positioned at the point (0, 1, 0) in camera coordinates is a "head lamp" fixed at a distance of 1 above the camera.

A 3D plot may contain several cameras. Changing the state of `CameraCoordinates` for
a light affects its relation to *all* cameras of
a scene. With `CameraCoordinates` = `TRUE`,
the position of the light in 3 space changes, when a new camera is
chosen interactively.

We define a sphere:

sphere := plot::Spherical( [1, u, v], u = 0..2*PI, v = 0..PI, FillColorType = Functional, FillColorFunction = proc(u, v) begin [(2 + cos(2*u))/3, (2 + sin(2*u))/3, 0] end_proc):

We define sunlight shining from above:

sunlight := plot::DistantLight([0, 0, 1], [0, 0, 0]): plot(sphere, sunlight):

Next, the sunlight is defined relative to the camera. In camera
coordinates, "above the camera" is given by the `Position``[0,
1, 0]`. Because the camera points downwards, we set the direction
of the sunlight "behind" the camera as well by choosing
the direction `[0, 1, -1.5]` w.r.t. the camera:

sunlight := plot::DistantLight([0, 1, -1.5], [0, 0, 0], CameraCoordinates = TRUE): plot(sphere, sunlight):

delete sphere, sunlight, pointlight:

We define the same sphere as in the previous example:

sphere := plot::Spherical( [1, u, v], u = 0..2*PI, v = 0..PI, FillColorType = Functional, FillColorFunction = proc(u, v) begin [(2 + cos(2*u))/3, (2 + sin(2*u))/3, 0] end_proc):

We define an animated camera. First, we use sunlight fixed in space:

camera := plot::Camera([-3*sin(a), -3*cos(a), 2], [0, 0, 0], 0.3*PI, a = 0..2*PI): sunlight:= plot::DistantLight([0, -2, 3], [0, 0, 0]): plot(sphere, camera, sunlight):

Next, we use sunlight moving with the camera:

sunlight:= plot::DistantLight([0, 3, -2], [0, 0, 0], CameraCoordinates = TRUE): plot(sphere, camera, sunlight):

We define a point light that is fixed to some point above the camera:

pointlight := plot::PointLight([0, 1, 0], CameraCoordinates = TRUE): plot(sphere, camera, pointlight):

delete sphere, camera, sunlight, pointlight:

We define the same sphere as in the previous examples:

sphere := plot::Spherical( [1, u, v], u = 0..2*PI, v = 0..PI, FillColorType = Functional, FillColorFunction = proc(u, v) begin [(2 + cos(2*u))/3, (2 + sin(2*u))/3, 0] end_proc):

We define an animated point light that is positioned below the camera initially. It moves to some point above the camera during the animation:

pointlight := plot::PointLight([0, 10*a, 0], a = -1..1, CameraCoordinates = TRUE): plot(sphere, pointlight):

We define an animated point light that is positioned to the left of the camera initially. It moves to the right of the camera:

pointlight := plot::PointLight([10*a, 0, 0], a = -1 .. 1, CameraCoordinates = TRUE): plot(sphere, pointlight):

delete sphere, pointlight:

`LightColor`|`LightIntensity`|`Position`|`SpotAngle`|`Target`

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