Horizon

Horizon in the distance of a scene

The horizon of a scene is the edge of vision at the height of the camera, parallel with the world coordinate plane. You can view the horizon in camera viewports.

A camera is level when it and its target are the same height from the world coordinate plane. In other words, the camera's local Z axis is parallel to the world plane. When the camera is level, the horizon line is centered in the viewport. As the camera tilts up, the horizon line lowers; as it tilts down, the horizon line raises.

The horizon line can help you match the perspective of your scene to the perspective of a still image. In general, matching perspective involves the following steps:

Display the horizon line. Use it to help you adjust the camera and target so they are level.
Display the image in the camera viewport. Use Views menu > Background Image.
Orbit the camera until the perspective of the scene roughly matches that of the still image.
Adjust the camera's perspective to fine-tune the perspective match.
Move the camera or target to position the scene against the background.

If you raise or lower the camera, raise or lower the target by an equal amount, in order to keep them level and maintain the horizon.