Theauthor isindebted toDr.M.CohnandDr.NX.L.Eastman for thetrail wouldoverwrite thestored image. several interesting discussions, andespecially toEugene Ottforsev- 3)Pointing toastored image ontheDVST,subsequent towrit-
Gordon A. Rose · 1965
segments. Thedistinction ismadebya pressure operated pentip switch. Wanted track coordinates arefiled byinterrupting thecom- ABSTRACT puter either atregular intervals (20ms),or,whenthetrack isstarted Techniques arepresented whichenable conventional light-pen orterminated, orcrosses gridlines ofpreselected spacing. tracking andpointing functions tobeextended tothedirect view Theneed totransport thebeamtoeverytrack startandthe storage tube(DVST). Theschemes eliminate thehigh datatransfer attendant unwanted image trails are disadvantages ofthephoto- rconsiderable buffer storage required evenforstatic displays sensormethod. Theclutter ofincidental trails (particularly noticeable ratenshort persistence cathode . . , a . whenbuilding upacomplex freehand sketch ofsymbols ordiagrams whenshort persistence cathode raytub)es (CRTs)areused. g o Twosolutions, aquadruple photo-sensor penandthepotenti- involving frequent penlifts andreturnreferencing), may bere- ometer pen(atransparent resistive sheet andstylus combination movedbyflood erasureandredisplay; butthis canbedemanding oino which coversthedisplay), aredescribed andcompared. computer timeifrepeated eachtime a wanted track iscommenced, . ¢ . . ~~~~~~~~~cient toconstrain this rotation. facilities iswellrecognized asa creative toolforon-line machine- aided design (I,(2), problem solving (3), textandprogramediting,Objection 3)hasbeenovercome inseveral ways. A single flood- Inmany instances, theextension ofpen displays toa number of eraseandredisplay cycle initiated eachtimea feature ispointed to indet ndnttatonsisesiabc.., a .. enables the convenitional photo-sensor pointing mode to be used. . ~~~~~~~~~~~~puter oninterrupt), isseenbytheoperator andbecomes hisfocal penmovementbyprobing thevisual field ofthepen), andinthe pitfrtakn.Mslgmn ftecnrle ptadtesyu pointing mode(which associates theinstant ofpenresponse withan dosntaprasnerrinheytm,btahrasnanync iteminthedisplay file), forthefollowing reasons: