scanning direction
In facsimile transmitting equipment, the scanning of an object, such as a message surface or the developed plane in the case of a drum, along parallel lines in a specified pattern.
Note 1: The scanning direction is equivalent to scanning over a right-hand helix on a drum.
Note 2: The orientation of the message on the scanning plane will depend upon its dimensions.
Note 3: In facsimile receiving equipment, scanning from right to left and top to bottom, is called “positive” reception and from left to right and top to bottom, is called “negative” reception.
Note 4: Scanning direction conventions are included in ITU-T Recommendations for phototelegraphic equipment.