Desktops can be displayed in landscape or portrait orientation.
Within the system display settings there is an option to rotate the individual monitors between 0, 90, 180 and 270 degrees:
When the driver's daemon process runs at startup it notifies the driver of the monitor metrics, including rotation angle.
The daemon monitors and informs the driver of any display changes which intern adjusts calibration accordingly.
In Windows XP, 7, 8, MacOS and Linux the driver will cater for the degree of rotation when posting co-ordinate data into the OS.
For Windows 10 in standard video card configurations utilising the native video drivers no adjustment is made by the driver as this is catered for within the OS. However, when using specialised graphics cards using their own video driver, it may be necessary for the driver to adjust co-ordinates. In this case the global setting use_native_screen_rotation can be set to enable co-ordinate adjustment. Currently this only relates to Windows 10 when using the UPDD Touch interface (virtual HID).
Further, in cases where UPDD Daemon is not running on a system with a fixed non-zero rotation angle and precalibrated data the rotated angle for a given touch device/display the rotation value can be predefined. This is held in the device setting private.screen_rotation.angle.