Carrol Touch TouchSystems CarrollTouch Prog, Programmer'S Manual

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Chapter 3 - General Programming Issues CARROLL TOUCH
3-6 Touch System Programmer’s Guide
Calibration
The size of the display area of the video monitor frequently does not
match the size of the touch active area of the touch frame. The touch
active area is usually larger than the display area. The relationship of
touch and video coordinates is shown in Figure 3-5. In addition, the
display area on most video monitors may actually shift position or drift,
while the touch active area remains constant. To establish and maintain
alignment of the touch active area with the active display area, the touch
screen must be calibrated. A calibration procedure such as the one that
follows identifies the touch coordinates of the extreme outside corners
of the video image displayed on the monitor and derives calibration
parameters that may then be used to convert touch coordinates into
video coordinates.
Figure 3-5. Touch Calibration Screen
It is strongly recommended that a calibration program be included in any
touch application or driver. Touch applications or drivers should not use
hard-wired values that are specific to a particular touch frame and
monitor. Use of a calibration program takes care of variations in monitor
image size and location and allows touch applications to be used on
different sizes of monitors and/or touch systems without modifying the
touch application or driver.
This calibration must be performed at least once for each physical touch
screen/video monitor pair. This procedure produces four calibration
parameters that should be stored by the host computer in some form of
nonvolatile storage, which lets the calibration be performed only once.
0
0
0
0
TOUCH_MAX_Y
VIDEO_MAX_Y
VIDEO_MAX_X
TOUCH_MAX_X