Terms and definitions

 Axis of Vision   (AV) Horizontal Line  (HL) Picture Plane  (PP) Center Line of Vision  (CLV) Plane of Vision  (PV) Stand Point  (SP) Eye Level Line  (EL) Vanishing Line (VL) Ground Plane  (GP) Vanishing Point (VP)

Stand Point (SP) refers to the position of the artist, as e.g. on the rocks before the Lighthouse (figg.1 and 2).

Ground Plane (GP) refers to a horizontal plane at the site of the Stand Point (SP), (figg. 1 and 2).

The Center Line of Vision (CLV) or Axis of Vision (AV) is identical to the axis of the lens of each eye. Each eye has its own CLV. Frequently the term Center Line of Vision (CVL) is understood as the mid-line in-between the CLVs of each eye, referring to the fact, that the optical input from each eye is unified to one single cerebral optical impression.

Looking at the red, yellow and blue objects (fig. 3) using both eyes, shows them as located on the mid-line c of the CLV of the two eyes. Looking at them separately by keeping one eye closed, shows different orders of arrangement for the left and the right eye.

The Picture Plane (PP) is an imaginary plane perpendicular to the Center Line of Vision (CLV) or the Axis of Vision (AV). It is a plane on which the scenery can be imagined as being projected on. The proportion of the objects on this projected image are equal to those of the image on the retina. The Picture Plane (PP) can be  assumed arbitrarily at any distance. Set e.g. at about 45 cm from the eye, it allows to take measure suitable to create a layout of the image to be created on the drawing bloc (see “How to draw“).

Each eye has its own Picture Plane (PP) and the images produced on each retina differ slightly from each other as explained in figure 3. As the images created on each retina are integrated to a single cerebral image, the term Picture Plane (PP) applies frequently to this centrally created picture, thus to the Picture Plane (PP) of the Center Line of Vision (CVL) of both eyes.

The Plane of Vision (PV) is a plane defined by the Center Lines of Vision (CLV) or the Axis of Vision (AV) of the two eyes.

The Horizontal Line (HL) or Eye Level Line (EL) is a line on the Picture Plane (PP) presenting the Vanishing Line (VL) of the Plane of Vision (PV) and/or of the Ground Plane (PL).

Under condition e.g. of a cloudy sky concealing the horizon (figure 5), the Horizontal Line (HL) still maintains its conceptual function as a line of repair remaining located in the same position.

If the eyes are fixed on any other location than the horizon, such as on the birds up on the sky (fig 2), the Horizontal Line (HL) of the Plane of Vision (PV), (fig. 7) and the Horizontal Line (HL) of the Ground Plane (GP) are no more identical - or in other words, they are only identical, if the Plane of Vision (PV) is parallel to the Ground Plane (GP).

Vanishing Point (VP) : Parallel lines such as the borders of a street,  the railings of a stair or the rays of the sun converge to a single point the Vanishing Point (VP). Lines parallel to the Picture Plane (PP) do not converge.