GTCO Summagrid IV - Users Guide Part 1 - Manual (Page 14)

Summagrid IV 14
3.1 Operational Overview
3.1.1 Overview
Summagrid IV is a digitizer. A digitizer is an input device that translates graphic
information, such as a drawing or photograph, into a computer readable format.
The Summagrid IV has two main parts: tablet and pointing device. The pointing
device may either be the stylus or cursor. The stylus/cursor emits a low-intensity
signal. A grid within the tablet reads this signal with the stylus/cursor is moved
across the tablet.
Therefore, for the tablet grid to sense this signal, the stylus/cursor must be used
over the grid, or active area and close enough to the grid, or in proximity. (Active
area and proximity are described below.) The Summagrid IV expresses the
stylus/cursor position as an X, Y coordinate pair, which is called a report. Valid
reports can only be collected when the stylus/cursor is in the tablet’s active area and
in proximity. Reports are in absolute coordinates (measured from the tablet’s
origin) and are expressed in inches, millimeters or counts of resolution (described
below).
3.1.1.1 Active Area
The active area is the region on the tablet surface in which the stylus/cursor
position can be identified. It’s marked on the tablet by corner brackets.
3.1.1.2 Proximity
Proximity is the maximum distance above the active area that the stylus/cursor
can be held and report a position. The proximity limit for the Summagrid IV is
.50”. Together, the active area and proximity establish a three-dimensional
volume within which the stylus/cursor can issue reports. Reports issued from
outside this volume are out of proximity (out-of-prox) and, therefore, do not
represent the current position of the stylus/cursor.
3.1.1.3 Resolution
Resolution is the “fineness” of detail that the tablet can distinguish. Resolution is
expressed in lines per inch (lpi) or lines per millimeter (lpmm).
Reports are measured in counts of resolution. One count is the distance
between two lines of resolution. As shown below, each square is one count of