Well, from the API documentation on the Sketchup::Camera class …
The Camera class contains methods for creating and manipulating a camera. The camera in SketchUp is the “point of view” from which you look at the model.
Since the text is personifying this action (using the pronoun you,) they decided to also use the term “eye”, since this is what you look at things with.
In actuality, (code-wise) the “eye” is a property of a camera object. (Everything in Ruby is an object.)
In Ruby properties are also sometimes referred to as attributes, which are implemented in pure Ruby objects by wrapping instance variables. (FYI, these pure Ruby attributes are not the same as data that SketchUp stores in Attribute Dictionaries.) But SketchUp API objects are C++ side objects with Ruby wrappers, that are exposed via getter and setter methods.
So we look at the API documentation for the Camera class, and it’s #eye() instance “getter” method:
Sketchup::Camera#eye()
and we see that the description …
The eye method is used to retrieve the eye Point3d object for the Camera.
This indicates it returns a Geom::Point3d object.
Basically, this is the point (expressed as 3 coordinates, x, y, z,) in 3D space of a viewing camera.
(I’m not sure if we would consider it to be the center of the lens, or the camera’s focal point. I lean toward the latter.)
But the API camera object’s do not have individual setter instance methods for all of the basic orientation properties. Instead the API coders decided to implement one “setter” method to set all 5 at once.
Ie: Sketchup::Camera#set()
The target of the camera, is the point in 3D space (Geom::Point3d object,) that the camera is looking at.
This sets up a vector (Geom::Vector3d) object, from the eye point, to the target point, called the direction.
Ie: Sketchup::Camera#direction()
Lastly, the camera has a up vector, from the eye point, perpendicular to the camera’s directional vector, pointing towards the “virtual” top of the camera (or towards the top middle of the viewport, as viewed through the camera.)
This allows you to rotate the camera around the eyepoint like in these plugins:
-
SCF: [Plugin] Camera Tools (0.3.1b) - By Thomas Thomassen
which was used to create this rotated render (in that thread) of a Volkswagen GTI:
[Plugin] Camera Tools • sketchUcation • 1