Browse Prior Art Database

Tracking Blob for Light Pen Graphics Devices

IP.com Disclosure Number: IPCOM000077733D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Giddings, GM: AUTHOR

Abstract

In light-pen cathode-ray tube (CRT) graphics, the "tracking blob" moves across the CRT with the light pen as it is moved, the x-y coordinates being sent to the computer when the light-pen switch is depressed. Two complementary methods are presented for tracking, a high resolution tracking method without hysteresis for movements which maintain the blob center point in view of the pen, and a coarse tracking method for ascertaining the location of the pen when light-pen detection of the center point has been lost. Both methods are implementable without need for arithmetic instructions in the graphics controller, and minimize core or hardware requirements.

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Tracking Blob for Light Pen Graphics Devices

In light-pen cathode-ray tube (CRT) graphics, the "tracking blob" moves across the CRT with the light pen as it is moved, the x-y coordinates being sent to the computer when the light-pen switch is depressed. Two complementary methods are presented for tracking, a high resolution tracking method without hysteresis for movements which maintain the blob center point in view of the pen, and a coarse tracking method for ascertaining the location of the pen when light- pen detection of the center point has been lost. Both methods are implementable without need for arithmetic instructions in the graphics controller, and minimize core or hardware requirements.

The fine tracking method is shown by Fig. 1 and comprises initially displaying the center point 10. If it is detected, the point is displayed one raster unit 11 (approximately 0.01 inch) to the right. If the point is still detected, the method loops back to repeat the same step until the right edge 12 of the light pen is encountered 13. Then, a new starting point is displayed N1 steps, say 3, to the left 11, at the presumed horizontal "center" of the pen. The same process is then conducted vertically to accomplish vertical positioning. A test for pen switch closure is then made. If the switch is closed, the current pen center is sent to the main CPU as an interrupt. The display picture is regenerated and then fine tracking is again attempted.

The coarse tracking method...