ondTouchsystem.Thissystemusesatechniquewhereacircuitiscapacitivelyclosedwhentheusertouchesthetable[].Interfaceslikethisoneusefrontprojectionduetotheopaquesurfaceneededforthesensors.OthersystemssuchasthemetaDESKalsousesensors,butintegratetheminphysicalobjectsthatcanbemanipulated[].Anothercommonapproachistousevideocamerastotrackinteractions.Forexample,theHoloWallusesasemi-opaquediffuserthatallowsinfrared(IR)lightprojectedfrombehindthescreentoreflectoffofobjectsatacertaindistancefromthesurface[].TheTouchLightinterfaceusestwoIRcamerastodeterminewhencontactwiththescreenhasoccurred[].Otherprojectionbasedsystems,liketheViCatuseoverheadcamerastotrackhandgestures[].Thistabledoesnotusephysicaltouchesonthesurface,butusesanoverheadcameratotrackhandgesturesinordertointeractwiththedisplay.Workisalsobeingdonetoimprovethenatureofmulti-touchinteraction.Theseareasofresearchareequallyvitaltothefieldasdesign只需要处理事件。