Abstract:
A device for animating a graphical or plastic representation comprises a support for the representation, an animation system for varying the representation and at least one sensor for detecting the presence of a person in a given field of view of the support and for generating a parameter representative of movements and/or gestures of a person in that field. It includes a control system which controls the animation system according to that parameter in response to the detection of a person. It also generates at least one random variable. The control system combines the random variable with the aforementioned parameter to command non-deterministic variations of the representation in response to movements and/or gestures of a detected person.

Description:
This application is a continuation of International PCT Application No. PCT/FR98/02328 filed on Oct. 30, 1998, which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a device for animating graphical or plastic representations and a system using it. 
     2. Description of the Prior Art 
     There are various systems for presenting different images on a common support, such as those used in certain advertising billboards. One such system displays for a preset time period an advertising poster initially wound around top and bottom members of the billboard support. Another system displays for a preset time period an advertising poster made up of juxtaposed vertical strips, each strip being fixed to one side of one of several triangular-profile members. In this way it is possible to display three different images in succession. 
     These devices can display static images only intermittently and for a preset time period, which tends to reduce the impact of the advertising message. Also, movement is used only to change from one image to another as quickly as possible, which tends to frustrate an observer who has not finished looking at the current image or reading the current message. 
     One object of the invention is to remedy boredom when observing a graphical or plastic representation by means of an animation device adapted to create an effect of surprise and variety. 
     SUMMARY OF THE INVENTION 
     To this end, the invention provides a device for animating a graphical or plastic representation, comprising support means for said representation, animation means for varying said representation, at least one sensor for detecting the presence of a person in a given field of view of said support means and for generating a parameter representative of movements and/or gestures of a person in said field, means for controlling said animation means according to said parameter in response to the detection of a person, and means for generating at least one random variable, wherein said control means include means for combining said random variable with said parameter to command non-deterministic variations of said representation in response to said movements and/or gestures. 
     The invention also provides the following features: 
     said sensor includes means for measuring the distance of a detected person from said support means; 
     said sensor is an ultrasound sensor; 
     the device includes a plurality of sensors, means for generating a plurality of parameters according to signals delivered by said sensors and means for generating a current state variable of said device according to said parameters and said random variable, said control means controlling said animation means according to said current state variable; 
     said sensors comprise at least one of a brightness sensor and of a sound sensor respectively adapted to measure the ambient brightness and to detect sound in a field in which said device is placed; 
     said control means include means for storing a predefined list of state variables, said control means being adapted to control said animation means selectively according to the presence or absence of said current state variable in said list; 
     said control means include means for producing a predefined sequence of animation of said animation means according to said state variable and for selectively modifying the execution of said animation sequence according to at least one random variable; 
     said control means include means for selectively interrupting an animation sequence in progress in response to variation of said state variable; 
     said control means are adapted to control said animation means according to the time since said animation means were placed in a given configuration; 
     said support means comprise at least one fixed support of a background graphical representation and at least one movable support of a foreground graphical representation and said animation means comprise means for moving said foreground representation movable support relative to said background representation fixed support; 
     said support means comprise a screen for displaying a video image and said animation means include means for processing said video image. 
     The device according to the invention is used to animate or to modulate parts of a graphic or plastic representation interactively, i.e. according to environmental parameters measured by electronic sensors. Also, the device according to the invention introduces a random element into the choice and execution of the animation. Taking a random variable into account in the choice and execution of an animation attracts and retains the interest of an observer, as it appeals to their curiosity. The observer wonders, and attempts to identify, which events or combinations of events influence the animation in progress. Moreover, the fact that the animation is rendered non-deterministic by the random variable maintains the effect of surprise and variety, since the same situations can produce significantly different effects. Finally, this also reduces the mechanical or robotic aspect of the animation and strengthens its esthetic impact since the observer appears to perceive a guiding “intelligence” beyond that of a simple robot or automaton. 
     According to the invention, the graphical or plastic representation also changes in accordance with the reactions of the observer. The device therefore involves the observer personally and directly in the communication established by the graphical or plastic representation and therefore establishes a real two-way communication with the observer. Another advantage of the device is that it enables multiple variants of a graphical or plastic representation to be shown, so maintaining the effect of variety and surprise and avoiding the boredom. 
     The invention also provides a system for animating graphical or plastic representations comprising: 
     a plurality of devices for animating graphical or plastic representations, each said device comprising support means for said representation, animation means for varying said representation, at least one sensor for detecting the presence of a person in a given field of view of said support means and for generating a parameter representative of movements and/or gestures of a person in said field, means for controlling said animation means according to said parameter in response to the detection of a person, and means for generating at least one random variable, said control means including means for combining said random variable with said parameter to command non-deterministic variations of said representation in response to said movements and/or gestures, 
     means for enabling communication between said devices, and 
     means for controlling the animation means of at least some of said devices according to the state of the control means of at least one of said devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood in the light of the accompanying drawings, in which: 
     FIG. 1 is a plan view of the front face of one element of a graphical representation animated by a device constituting a first embodiment of the invention; 
     FIG. 2 is a plan view of the rear face of the graphical representation element from FIG. 1; 
     FIG. 3 is a view in section taken along the line  3 — 3  of a system for imparting movement in translation used in the first embodiment of the device according to the invention; 
     FIG. 4 is a block diagram of an electronic control system of the first embodiment of the device according to the invention shown in FIGS. 1 to  3 ; 
     FIG. 5 is a block diagram of an electronic control system of a second embodiment of a device according to the invention; 
     FIG. 6 is a diagram showing how the device according to the invention changes state according to sensor measurements and a random variable; 
     FIG. 7 is a flowchart showing three processes necessary for implementing the animation device according to the invention; 
     FIG. 8 is a flowchart showing how a random variable is introduced into the choice of an animation sequence; 
     FIG. 9 is a flowchart showing how a random variable is introduced into the execution of a current animation sequence; and 
     FIG. 10 is a flowchart showing how actuators are controlled in the first embodiment of the invention shown in FIGS. 1 to  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 to  3 , a first embodiment of an animation device according to the invention includes a generally rectangular fixed background graphical representation support  1 , a first mobile foreground graphical representation support  2  that can move parallel to the top and bottom edges of the background graphical representation support  1  and a second foreground graphical representation support  3  which can rotate about a rotation axis  4 . The background graphical representation support  1  can be a painted canvas, a photograph or any other type of graphical or pictorial representation. 
     The distances between the background graphical representation support  1  and the foreground mobile graphical representation supports  2  and  3  are defined so that the moving members can cross without impeding each other&#39;s movement. 
     The background graphical representation support  1  is supported by a rectangular frame  8  which makes the assembly rigid. 
     In the embodiment shown in FIG. 1, a unit  5  combining several electronic sensors is fixed by a fixing lug  7  to the rear side of the bottom edge of the frame  8  supporting the graphical representation support  1 . An opening  6  in the unit  5  enables the electronic sensors to react to the presence of an observer. 
     In a first embodiment of the invention, shown in FIG. 2, an electric motor  9  rotates the mobile member  3  about the axis  4  directly or via a speed reduction system of pulleys or gears. 
     The top and bottom parts of the mobile member  2  moving in translation are fixed to U-sections  10  and  11  sliding on respective angle-irons  12  and  13  fixed to the top and bottom members of the frame  8 . 
     The U-sections  10  and  11  are joined together by a link  14  connected to the motor  15  by way of an attachment point  16  and a transmission belt  17 . The transmission belt  17  is tensioned between the motor  15  and pulley by a tension spring  18 . 
     End of travel switches  19  and  20  detect the end of travel of the mobile member  2  in its extreme positions, after the U-section  10  abuts on them. The end of travel switches  19  and  20  can employ mechanical or magnetic contacts. In the latter case, the magnets which make the electrical contact are fixed to one of the U-sections  10  of the mobile support. 
     An electronic printed circuit  21  includes signal processing, control, power supply regulation electronic circuits and a processor. The printed circuit  21  is connected to the sensors in the unit  5  via a ribbon cable  24 . It is also connected to the end of travel switches  19  and  20  and the motors  9  and  15 . Finally, it is connected to the AC line voltage via a mains adapter  22  and its connecting cable  23 . 
     FIG. 3 shows in section a mechanism for imparting movement in translation used in the device shown in FIGS. 1 and 2. The purpose of this mechanism is to bring about low-friction sliding of the support  2  relative to the support  1 . The U-sections  10  and  11  are adjusted to cover the respective angle-irons  12  and  13  completely and the front panel of the background graphical representation support  1  partially. The inside of the U-sections  10  and  11  is covered with a plastics material  25  to facilitate relative sliding between them and the angle-irons  12  and  13 . 
     The link  14  is fixed to the U-sections  10  and  11  by screws  26 . The mobile support  2  is fixed to the front face of the U-sections  10  and  11 . In an embodiment that is not shown, and in order to move mobile supports whose size is such that they do not cover the entire height of the background graphical representation support  1 , the mobile support  2  is held and guided by a single top or bottom U-section  10  or  11 . In another embodiment, also not shown, the mobile support  2  can be guided and held by lateral Usections, thereby sliding on the left and right members of the frame  8 . 
     As shown in section in FIG. 3, the device as a whole is placed in an “American system” type frame  27  fixed to the right and left members of the frame  8 . The unit  5  containing the sensors, in which there is a window  6 , is fixed by the fixing lug  7  to the rear face of the bottom member of the “American system” frame  27 , rather than directly to the frame  8  as shown in FIGS. 1 and 2. 
     When the device is switched on, the mobile graphical representation supports  2  and  3  move toward their reference position. The top U-section  10  comes into contact with the switch  19 , which determines the reference position of the mobile support  2 . The control electronic circuit on the printed circuit  21  takes account of the parameters of the environment of the device by means of sensors such as brightness sensors and sensors which detect the presence of an observer and the distance to the observer. The control electronic circuit initiates and executes a sequence of prerecorded movements of the mobile supports  2  and  3  by controlling the motors  15  and  9  accordingly. The choice of the sequence of movements and the execution of the sequence chosen are functions of the environmental parameters and a random variable. 
     The sensors in the unit  5  respond to any change in the environment such as movement of the observer or a change of brightness. The control electronic circuit can interrupt the sequence in progress and start a new one. 
     Referring to FIG. 4, the electronic control system of the first embodiment of a device according to the invention shown in FIGS. 1 to  3  is based on a microcontroller  41  connected to sensors and actuators. The microcontroller  41  includes a processor  44  clocked by a clock  45 , a non-volatile PROM or Flash PROM  47  containing the software, a volatile RAM  46  containing the variables, one or more analog/digital converters  42  and digital inputs/outputs  43  of the microcontroller  41 . 
     A brightness sensor  30  is connected to the microcontroller  41  through a sensor output signal processing circuit  31 . The processing circuit  31  can be either a threshold detector or an amplifier circuit. A threshold detector applies to the input of the microcontroller a binary signal which is a function of a predefined brightness threshold. 
     An amplifier circuit applies to the input of the analog/digital converter  42  a signal representative of the ambient brightness. 
     A microphone  32  is connected to the microcontroller  41  via an audio processing circuit  33 . The circuit  33  can be an amplifier circuit, a spectrum analyzer or a voice recognition circuit. 
     In the case of an amplifier circuit, it delivers the amplified audio signal to the analog/digital converter  42 . The signal is then sampled by the analog/digital converter  42  at a frequency which is twice the highest frequency to be measured. 
     If the audio processing circuit  33  is an audio spectrum analyzer, the outputs of the processing circuit deliver analog signals whose values are representative of the amplitudes of the audio signal in each frequency band. Both outputs are applied to a plurality of analog/digital converters in order to deliver to the processor  44  values representative of the intensity of the signal in the predefined frequency bands. 
     If the audio signal processing circuit  33  is a voice recognition circuit, words to be recognized are stored in a dedicated integrated circuit via the microphone  32 . If the observer says a word that has previously been stored, the voice recognition circuit activates the output corresponding to that word and indicates it to the processor  44 . 
     An infrared light sensor  34  is connected to the microcontroller  41  via an infrared processing circuit  35 . The infrared processing circuit  35  can be either an amplifier circuit or a decoder circuit associated with an infrared remote controller. 
     If the infrared processing circuit  35  is an infrared amplifier, it delivers to the microcontroller  41 , after filtering out ambient infrared radiation, a binary signal corresponding to the infrared signal emitted by any audio or video remote controller. The processor  44  can therefore detect the presence of an infrared emission by sampling the received signal. 
     If the infrared processing circuit  35  is an infrared decoder associated with a specific infrared remote controller supplied with the device according to the invention, the infrared decoder  35  transmits to the microcontroller  41  a digital signal which identifies the key pressed on the remote controller. 
     An ultrasound emitter  36 , an ultrasound receiver  37  and an ultrasound transmit/receive circuit  38  constitute a circuit for detecting the observer or measuring the distance to the observer. This circuit delivers to the microcontroller  41  a signal representative of the time elapsed between ultrasound pulses leaving the ultrasound emitter  36  and being picked up by the ultrasound receiver  37  after they are reflected by the body of the observer. 
     In an embodiment that is not shown, the multiplicity of ultrasound emitters  36  and ultrasound receivers  37  are disposed horizontally below the bottom member of the graphical representation. The ultrasound receivers  37  detect movements of the observer, not only when they move around within the space covered by the sensors, but also movements of their arms (e.g. arms crossed or held out to the front). 
     The device according to the invention can include one or more other sensors  39 , such as a passive infrared sensor, an electrostatic sensor, a thermal sensor or contact sensors such as switches or pressure sensors. The processing circuits  40  associated with these other sensors  39  can be of the threshold detector type delivering a binary signal or of the amplifier type associated with an analog/digital converter, as appropriate. 
     In embodiments that are not shown, the various sensors responsive to the presence of the observer and parameters of the environment can be placed directly on the background graphical representation support  1  or combined in an L-shaped cover partly covering one end of the background graphical representation support  1 . 
     FIG. 4 shows also actuators that can be used in the first embodiment of the device according to the invention. 
     One or more stepper motors  15  are connected to the microcontroller  41  via a stepper motor control circuit  48 . The control circuit  48  delivers the current necessary to drive the motors, monitors their rotation direction and delivers the step pulses, and therefore the number of steps to be effected and the rotation speed of each of the stepper motors. 
     One or more servomotors  9  are connected to the microcontroller  41  via a control circuit  49  for the servomotors  9 . The control circuit  49  delivers to the servomotors  9  pulse-width-modulated pulses representative of the position that the servomotors must maintain and the current necessary to drive them and to maintain their position. 
     One or more DC motors  51  can be connected to the microcontroller  41  via a DC motor control circuit  50 . The control circuit  50  delivers the current to drive them and monitors their direction and speed of rotation. 
     Other actuators  53  can be controlled by the microcontroller  41 , such as synchronous motors, light-emitting diodes or incandescent lamps, perfume diffusers or audio amplifiers associated with loudspeakers for reproducing prerecorded sounds. The control circuits  52  for the other actuators  53  deliver the necessary signals and power for them to operate. 
     The operation of the electronic control system of the first embodiment of the device described hereinabove will now be described. 
     If an observer approaches the system, they are detected by the circuit  38  for measuring the distance to the observer, which supplies an indication of that distance to the microcontroller  41 . The information is combined with values measured by other sensors and with a random variable generated by the processor  44  in order to choose one sequence from the animation sequences stored in the PROM  47 . The processor  44  interprets and executes the steps of the chosen sequence by positioning the motors  15 ,  9  and  51  at prerecorded positions and modulating movement parameters such as speed and delay according to random variables. If the observer approaches and speaks, this triggers an animation sequence informing them that their communication is being taken into account. Thus any variation in the parameters measured by the sensors is taken into account in choosing and executing these sequences. 
     In a second embodiment of the invention, shown in FIG. 5, the system according to the invention uses a liquid crystal screen  54  in place of the background and foreground graphical and/or pictorial representation supports driven by electric motors. 
     The second embodiment of the device changes some parts or the whole of the image displayed. The parameters of the image that can change according to the measurements effected by the sensors are the brightness, contrast, color saturation, viewing angle, position and color of the light source, for example. In an embodiment of this kind elements of the image can be moved by fusing, superposing or deforming (“morphing”) one part of the image with another. 
     In a third embodiment of the invention, not shown, the system according to the invention is used to animate parts of a plastic representation such as a sculpture. This embodiment of the device changes one or more elements of the plastic representation in three dimensions. In this case, the control electronics, motors and sensors are accommodated in one or more elements of the plastic representation or in a plinth to which it is secured. 
     The invention will now be described with reference to the diagrams and flowcharts of FIGS. 6 to  10 . Hereinafter: 
     the term “state variable” refers to a logical combination of the state of the sensors at a given time combined with one or more random variables generated by the system, and 
     the term “event” refers to a movement, a wait or a branch. 
     A movement is a situation in which a part of the graphical representation changes from a start configuration to an end configuration within a predetermined time period. 
     A wait is a period of time during which a part of the graphical representation which can be animated remains unchanged. 
     A branch is a command to run a new animation sequence. 
     An animation sequence is a succession of predefined movement, wait or branch events which is executed according to a state variable. Like an event, a sequence can be interruptible or non-interruptible. Each event of a sequence can be modulated by one or more random variables. 
     The state of the system or the device is the set of animation sequences to be executed in response to a particular state variable. 
     FIG. 6 is a diagram showing how the system generates a state variable according to measurements performed with the aid of the sensors and a random variable generated by the microcontroller  41 . The diagram is a state diagram of the kind used to describe a finite state machine. The circles  60 ,  61  and  62  represent states of the system corresponding to the set of prerecorded animation sequences that can be executed and modified. FIG. 6 shows an embodiment which comprises seven system states: a Sleeping state, two Waking states, two Going to sleep states and two intermediate states. The arrows  64  and  65  represent the state variables which enable the system to leave the Sleeping state and the arrows  63  and  66  define the state variables which cause the system to remain in the Sleeping state or the Waking state  1 , respectively. 
     For example, if the ambient brightness is very low or even zero around the device, and if the state variable  63  is defined by the clause “IF the value of the brightness sensor is 0 OR if it is 1 for less than 15 seconds THEN go to the Sleeping state”, the system executes the animation sequence associated with the Sleeping state. To give another example, event  64  is defined by the clause “IF brightness sensor=1 AND random variable≧80% THEN go to Waking state 1” and the event  65  is defined by the clause “IF brightness sensor=1 AND random variable&lt;80% AND observer at less than 3 meters THEN go to Waking state 2”. If a person enters the room in which the device is located, turns on the light and approaches to within three meters of the device, it executes the Waking  2  sequence in 80% of cases. This example shows how a random variable, generated by a change of sensor state, varies the animation sequence in order to maintain an effect of surprise and variety. 
     FIG. 7 shows the three processes necessary to implement the device according to the invention. After a reset phase on power up symbolized by the “Start” event  69 , the “Determine State” first process  70  defines the state of the system according to a state variable established by combining the state of the sensors with a random variable. The “Execute Sequence” second process  71  interprets, executes and modifies the prerecorded animation sequences corresponding to the current state of the system. The “Execute Movement” third process  72  animates the mobile parts of the graphical representation controlled by the device according to the events sent by the “Execute Sequence” process  71 . These processes execute in parallel and communicate with each other via global variables to enable virtually instantaneous movement in response to changes of the state of the sensors, if necessary. Each of the three processes is described in more detail below. 
     FIG. 8 is a flowchart showing the “Determine State” first process  70  from FIG.  7 . The flowchart shows how a random variable is introduced into the choice of the animation sequence to be performed. The “Start” event  69  symbolizes the reset phase executed on powering up the system and enabling proper execution of the three main processes from FIG.  7 . The state of the various sensors is first taken into account in step  73 . The system then generates a random variable in step  74 . That random variable is then combined with the state of the various sensors to create a state variable in step  75 . That state variable represents the state of the sensors at a time T combined with the random variable generated by the system in step  74 . 
     The state variable created in this way is used in step  76  to search a list of predefined state variables to see if there is a state corresponding to the state variable generated in step  75  (test  77 ). If yes, in step  78  the system performs a new test to determine if the state of the system corresponding to the state variable of step  75  involves a change of state relative to the current state. If yes, a change of state request is generated in step  79  and is acted on by the “Execute sequence” process  71 . 
     After step  79 , the system goes to step  80  which corresponds to a wait before repeating the process from step  73 . Likewise, if the result of test steps  77  and  78  is negative, the system returns to step  73  after the waiting step  80 . 
     FIG. 9 is the flowchart of the “Execute Sequence” process  71  from FIG.  7 . The flowchart shows the management of the animation sequences and how a new random variable affects the execution of the current animation sequence in order to maintain an effect of surprise and discovery. 
     The events of an animation sequence are characterized by parameters which can be modified by a random variable. For example, a movement is characterized by a final position, a speed, a movement profile and a parameter indicating to what degree the movement can be interrupted or not to start a new sequence after a change of state of the system. Each of these parameters of a movement can be modulated by one or more random variables to make the animation sequence slightly different each time it is executed. 
     Referring to FIG. 9, the “Start” step  81  corresponds to a reset phase executed when the system is powered up. A first test is performed in step  82  to determine if the event currently being executed must be terminated before executing the next one. If yes, a test step  83  determines if the event in progress has finished. If the result of test step  83  is negative, the system returns to step  82  after a waiting step  84 . If the result of test step  82  is negative (the current event must not be terminated before executing the next event) or the result of test step  83  is positive (event terminated), the system determines in step  85  if a new state is required. A change of state request can be sent in step  79  of the “Determine state” process (FIG.  8 ). If the response is in the affirmative (test step  85 ), the system determines in step  86  if the current sequence can be interrupted. If not (test step  86 ), the system returns to step  82  after a predefined waiting step  84 . If the result of the test step  86  is positive (the sequence can be interrupted), the system initializes an event pointer in step  88  to point to the first event of the animation sequence corresponding to the new state of the system. The event to be executed is read in step  89 . If the result of the test step  85  is negative (no change of state required), the event pointer is incremented in step  87  to point to the next event in the current animation sequence and the event to be executed is read in step  89 . 
     In step  90  the system determines if the event to be executed can be modulated, i.e. if some of its parameters can and must be modified according to a random variable. For example, the parameters of an event such as the speed of a movement, the length of a wait or the probability of a branch are parameters that can be modulated. If the result of the test step  90  is negative, the movement is executed without change in step  93 . If the result of the test step  90  is positive (event can be modulated), a random variable is generated in step  91 . In step  92  that random variable is combined with the parameters of the current event which can be modulated to create an event of the same type as that obtained in step  89  but in which the parameters which can be modulated may be different. The modulated event created in this way in step  92  is then executed in step  93 . In the case of a movement, execution consists in adding a movement to the list of the movements in progress, as described below. The process is then repeated from step  82  after a predefined waiting step  84 . 
     FIG. 10 is the flowchart of the “Execute Movement” process  72  from FIG.  7 . The flowchart shows how mobile parts of a graphical representation animated by the device according to the invention are moved. 
     The “Start” step  94  symbolizes the reset phase on powering up which is required for the process to be executed correctly. The system first determines in a test step  95  if there is at least one movement to be executed. If not, it waits for a particular period of time in step  96  before repeating the test in step  95 . If the result is positive, it increments the movement pointer in step  97  to select the movement to be managed from the list of movements in progress in step  98 . In step  99  a test determines if that movement has finished. If the result is positive, it updates the list of movements in progress in step  100  and returns to step  95  after the waiting step  96 . 
     In the case of a negative result of the test step  99  (the movement has not finished), the system determines the current phase of the movement in step  101 . The phase of a movement is an acceleration, deceleration or constant speed phase, depending on the movement profile. In step  102  the system determines the next position that the moving element must occupy from its current position, phase and speed. In step  103  the mobile element corresponding to the movement in progress is positioned at the position defined in step  102 . The system then waits for a predefined time period in step  96  before resuming the process at step  95 . 
     The animation device for graphical or plastic representations described above functions autonomously in accordance with parameters measured by the sensors and  10  random variable(s) generated by the processor  44 . 
     It is possible for a plurality of animation devices of the type described above, with different or the same representations, to communicate with each other via cable or wireless communication means. To this end, the microcontroller  41  of each device is equipped with a communication interface  55 , as shown in chain-dotted outline in FIGS. 4 and 5. This produces a system made up of a plurality of devices in which the graphical or plastic representations of some devices are slaved by their microcontroller  41  to those of one or more other devices, and consequently synchronized according to the state of the other device(s). For example, one of the devices can be master device and the others slave devices. 
     It goes without saying that the embodiments described are merely examples and that they can be modified without departing from the scope of the invention. Thus although the embodiment of the invention described hereinabove is illustrated by a twodimensional graphical or pictorial representation, the device and the system according to the invention can be applied to plastic representations in three dimensions, such as a sculpture.