Abstract:
An information input device includes a detection portion, a processor, and a memory. The detection portion is configured to detect a position of a writing portion being in contact with or close to the detection portion. The memory is configured to store computer-readable instructions. The computer-readable instructions, when executed by the processor, cause the information input device to perform processes that include acquiring position information at a predetermined time interval, setting, as first position information, information indicating one of positions indicated by the acquired position information, determining whether a distance between a position indicated by the set first position information and a position indicated by second position information is less than a threshold value, and storing, as information configuring trajectory information, the second position information in a storage portion in response to determining that the distance is not less than the threshold value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2013-197501 filed Sep. 24, 2013, the content of which is hereby incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an information input device that can acquire information input on a booklet-like recording medium in which a plurality of paper sheets are bound, and a non-transitory computer-readable medium storing computer-readable instructions. 
     An information input device is known that can digitize written content by reading a trajectory of a writing tool using a digitizer in a pad, when a character, a graphic, etc. are written on a paper medium on the pad using the writing tool. The digitizer detects a position of the writing tool that is in contact with or is close to a detection surface of the digitizer. The digitizer converts the detected position into coordinate data, taking the detection surface as an X-Y plane, and outputs the coordinate data to the information input device. The information input device samples the coordinate data output by the digitizer at a certain speed, and can acquire, as trajectory information, an aggregate of the coordinate data that can reproduce the trajectory of the writing tool. See, e.g., JP H5-67236A 
     SUMMARY 
     In a case where the writing speed using the writing tool is slow, if the coordinate data is sampled at a certain speed, in the same manner as in a case where the writing speed is fast, many pieces of coordinate data of proximate positions are obtained. Particularly, in a case where the writing tool stays in the same position for some time during writing, it is possible that the same coordinate data is consecutively acquired and the amount of data of the trajectory information is increased. 
     Embodiments of the broad principles derived herein provide an information input device and a non-transitory computer-readable medium storing computer-readable instructions that are capable of suppressing an increase in an amount of data of trajectory information by thinning out coordinate data of the same position or proximate positions. 
     Embodiments provide an information input device that includes a detection portion, a processor, and a memory. The detection portion is configured to detect a position of a writing portion being in contact with or close to the detection portion. The memory is configured to store computer-readable instructions. The computer-readable instructions, when executed by the processor, cause the information input device to perform processes that include acquiring position information at a predetermined time interval, the position information being information of the position detected by the detection portion, setting, as first position information, information indicating one of positions indicated by the acquired position information, determining whether a distance between a position indicated by the set first position information and a position indicated by second position information is less than a threshold value, the second position information being position information acquired after the first position information is acquired, and storing, as information configuring trajectory information, the second position information in a storage portion in response to determining that the distance is not less than the threshold value. The trajectory information is information indicating a trajectory of the writing portion. The setting, as the first position information, the information indicating the one of the positions indicated by the acquired position information includes setting, as the first position information, the second position information stored in the storage portion. 
     Embodiments also provide a non-transitory computer-readable medium storing computer-readable instructions that, when executed by a processor of an information input device, cause the information input device to perform processes that include acquiring position information at a predetermined time interval, the position information being information of a position detected by a detection portion, the detection portion being configured to detect a position of a writing portion being in contact with or close to the detection portion, setting, as first position information, information indicating one of positions indicated by the acquired position information, determining whether a distance between a position indicated by the set first position information and a position indicated by second position information is less than a threshold value, the second position information being position information acquired after the first position information is acquired, and storing, as information configuring trajectory information, the second position information in a storage portion in response to determining that the distance is not less than the threshold value. The trajectory information is information indicating a trajectory of the writing portion. The setting, as the first position information, the information indicating the one of the positions indicated by the acquired position information includes setting, as the first position information, the second position information stored in the storage portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be described below in detail with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of an information input device; 
         FIG. 2  is a block diagram showing an electrical configuration of the information input device; 
         FIG. 3  is a flowchart of main processing; 
         FIG. 4  is a diagram illustrating variables [NowPoint] and [LastPoint] used in the main processing, and coordinate data stored in stroke data; 
         FIG. 5  is a diagram illustrating a first modified example in which, when the acquired coordinate data indicates proximate coordinates of the coordinate data of [LastPoint], the acquired coordinate data is not added to the stroke data; and 
         FIG. 6  is a flowchart of main processing according to a second modified example. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment will be explained with reference to the drawings. An overview of an information input device  1  according to the present embodiment will be explained with reference to  FIG. 1 . In the explanation that follows, the upper left side, the lower right side, the top side, the bottom side, the lower left side, and the upper right side in  FIG. 1  are respectively the left side, the right side, the top side, the bottom side, the front side, and the rear side of the information input device  1 . 
     A user may use an electronic pen  3  to write information on a paper medium  100  that is mounted on the information input device  1 . The information input device  1  is a thin and lightweight handwriting input device that can detect and digitize positions of the electronic pen  3  over time. The information input device  1  includes housings  8 L and  8 R. The housings  8 L and  8 R are each made of resin and have a thin rectangular plate shape. The arrangement of the housings  8 L and  8 R can be changed between a state in which the housings  8 L and  8 R are open in a two-page spread in the left-right direction, as shown in  FIG. 1 , and an overlapped state (not shown in the drawings) in which the housings  8 L and  8 R are overlapped with each other. The housing  8 R houses a sensor board  71 , a sensor control board  28 , and a main board  20  (refer to  FIG. 2 ). The housing  8 L houses a sensor board  72  and a sensor control board  29  (refer to  FIG. 2 ). 
     The electronic pen  3  is a known electromagnetic induction-type of electronic pen and includes a core  31 , a coil  32 , a variable capacity capacitor  33 , a circuit board  34 , a capacitor  35 , and an ink storage portion  36 . The core  31  is provided in the tip portion of the electronic pen  3 . The core  31  is urged toward the tip of the electronic pen  3  by an elastic member that is not shown in the drawings. The tip portion of the core  31  protrudes to the outside of a cylindrical body  30 . The back end of the core  31  is connected to the ink storage portion  36 , which stores ink. The ink storage portion  36  supplies the ink to the core  31 . When the user uses the electronic pen  3  to perform writing on a paper sheet  120 , a written character (a text character, a numeric character, a graphic, etc.) may be formed by the ink on the paper sheet  120 . 
     The coil  32  is held between the core  31  and the variable capacity capacitor  33  in a state in which the coil  32  is wound around the ink storage portion  36 . The variable capacity capacitor  33  is fixed in place in the interior of the electronic pen  3  by the circuit board  34 . The capacitor  35  is mounted on the circuit board  34 . The capacitor  35  and the variable capacity capacitor  33  are connected in parallel with the coil  32  to configure a known resonance (synchronization) circuit. 
     The paper medium  100  is a booklet-like medium that can be opened out to a two-page spread in the left-right direction. The paper medium  100  is a paper medium in which a pair of cover sheets (a front cover sheet  110 L and a back cover sheet  110 R) and a plurality of paper sheets  120  are bound at their respective edge portions. As an example, the paper medium  100  is an A5 size notebook. The paper medium  100  is mounted on the information input device  1  such that the front cover sheet  110 L is placed on the upper surface of the housing  8 L and the back cover sheet  110 R is placed on the upper surface of the housing  8 R. The user can write information on the paper sheet  120  using the electronic pen  3  in a state in which the paper medium  100  is mounted on the information input device  1 . Position information of the electronic pen  3  that is used to write information on the paper medium  100  is detected by the sensor board  71  or  72  housed in the housing  8 L or  8 R on which the paper sheet  120 , on which the information is written, is placed. 
     An electrical configuration of the information input device  1  will be explained with reference to  FIG. 2 . The information input device  1  mainly includes the main board  20 , the sensor boards  71  and  72 , and the sensor control boards  28  and  29 . As described above, the housing  8 R houses the main board  20 , the sensor board  71 , and the sensor control board  28 . The housing  8 L houses the sensor board  72  and the sensor control board  29 . 
     The main board  20  is provided with a CPU  21 , a RAM  22 , a flash ROM  23 , and a wireless communication portion  24 . The RAM  22 , the flash ROM  23 , and the wireless communication portion  24  are electrically connected to the CPU  21 . The CPU  21  performs control of the information input device  1 . The RAM  22  temporarily stores various data, such as arithmetic operation data. The flash ROM  23  stores various programs that are used by the CPU  21  to control the information input device  1 . Further, the flash ROM  23  stores stroke data that indicates a trajectory of the electronic pen  3  that is used to write information on the paper medium  100 . The stroke data is structured by adding header information (a stroke header) to data in which a plurality of pieces of position information (coordinate data, for example) of the electronic pen  3  that are detected over time by the sensor board  71  and the sensor board  72  are arranged in an order of detection. The stroke header includes, for example, data piece number information, which indicates the number of pieces of coordinate data included in one set of the stroke data, and time information, which indicates a time at which the stroke data is generated. In other words, the stroke data is data that can reproduce information (a text character, a numeric character, a graphic, etc.) written on the paper sheet  120  by the user, by connecting the individual pieces of coordinate data along a time series. The wireless communication portion  24  is a controller that is used to perform near-field wireless communication with an external electronic device. Although not shown in the drawings, the information input device  1  can transmit the generated stroke data to a personal computer (PC) or the like used by the user, via the wireless communication portion  24 . 
     The sensor boards  71  and  72  are sensors that use an electromagnetic induction method to detect a position of the electronic pen  3  that is in contact with or is close to the sensor boards  71  and  72 . The sensor boards  71  and  72  each include a plurality of rectangular loop coils that are arranged at a predetermined interval in an X axis direction (the left-right direction) and a Y axis direction (the up-down direction). The sensor board  71  is electrically connected to an application-specific integrated circuit (ASIC)  28 A, which is mounted on the sensor control board  28 . An antenna resonance circuit is built into the sensor control board  28 . The ASIC  28 A controls the sensor board  71  and causes the sensor board  71  to perform an operation to detect a position of the electronic pen  3 . When a writing operation using the electronic pen  3  is performed on the housing  8 R, which houses the sensor board  71 , the ASIC  28 A generates coordinate data based on the position of the electronic pen  3  detected by the sensor board  71 . In a similar manner, the sensor board  72  is electrically connected to an ASIC  29 A, which is mounted on the sensor control board  29 . An antenna resonance circuit is built into the sensor control board  29 . The ASIC  29 A controls the sensor board  72  and causes the sensor board  72  to perform an operation to detect a position of the electronic pen  3 . When a writing operation using the electronic pen  3  is performed on the housing  8 L, which houses the sensor board  72 , the ASIC  29 A generates coordinate data based on the position of the electronic pen  3  detected by the sensor board  72 . Of the ASIC  28 A and the ASIC  29 A, the ASIC  28 A, which is on the master side, is directly connected to the CPU  21 , and outputs the coordinate data to the CPU  21 . The ASIC  29 A, which is on the slave side, is connected to the CPU  21  via the ASIC  28 A, and outputs the coordinate data to the CPU  21 . 
     The principle of an operation by which the sensor boards  71  and  72  detect positions of the electronic pen  3  (hereinafter, this operation is simply referred to as “scanning”) will be briefly explained. Based on an instruction of the CPU  21 , the ASIC  28 A and the ASIC  29 A control the sensor control boards  28  and  29 , respectively. The sensor control boards  28  and  29  cause an electric current of a specific frequency to flow through the plurality of loop coils of the sensor boards  71  and  72 , and generate a magnetic field. If the electronic pen  3  comes close to the sensor board  71  or  72  in this state, a resonance circuit of the electronic pen  3  is caused to resonate as a result of the electromagnetic induction of the loop coils, and an induction field is generated. 
     Next, the sensor control boards  28  and  29  stop the flow of the electric current to the loop coils and scans each of the loop coils. The electric current generated by the induction field that is caused by the resonance circuit of the electronic pen  3  flows through the loop coils. The electric current flowing through the loop coil that is closest to the electronic pen  3  is relatively large, and the electric current flowing through an adjacent loop coil is relatively small. The sensor control boards  28  and  29  convert the electric current that has flowed through each of the loop coils of the sensor boards  71  and  72  into a voltage value using a differential amplifier circuit (not shown in the drawings), and input the voltage value to the ASIC  28 A and the ASIC  29 A. The ASIC  28 A and the ASIC  29 A calculate the position of the electronic pen  3  based on the input voltage value, and output the calculated position to the CPU  21  as the coordinate data. 
     When the user is writing information on the paper medium  100  using the electronic pen  3 , a writing pressure is applied to the core body  31  of the electronic pen  3 . The inductance in the coil  32  varies according to the writing pressure applied to the core body  31 . Accordingly, the resonance frequency of the resonance circuit of the electronic pen  3  changes. The ASIC  28 A and the ASIC  29 A detect a change in the resonance frequency (a phase change) and determine whether or not information is being written on the paper medium  100 . When it is determined that the user is writing information on the paper medium  100  (the writing pressure is applied to the electronic pen  3 ) based on the change in the resonance frequency, the ASIC  28 A and the ASIC  29 A output a pen down signal (a high signal) to the CPU  21 . When it is determined that the user is not writing information on the paper medium  100  (the writing pressure of the electronic pen  3  is released) based on the change in the resonance frequency, the ASIC  28 A and the ASIC  29 A output a pen up signal (a low signal) to the CPU  21 . When the CPU  21  receives the pen down signal, the CPU  21  acquires the coordinate data output by the ASIC  28 A and the ASIC  29 A, generates stroke data, and stores the generated stroke data in the flash ROM  23 . 
     Main processing of the information input device  1  will be explained with reference to  FIG. 3  and  FIG. 4 . When the power source of the information input device  1  is turned on, the CPU  21  outputs an instruction to the ASIC  28 A and the ASIC  29 A, and supplies electric power to the sensor boards  71  and  72 . The ASIC  28 A and the ASIC  29 A start scanning using the sensor boards  71  and  72 . The CPU  21  reads the program stored in the flash ROM  23  into the RAM  22  and performs the main processing (refer to  FIG. 3 ). The main processing is processing in which the CPU  21  generates stroke data based on the coordinate data acquired from the ASIC  28 A and the ASIC  29 A. In the present embodiment, the CPU  21  thins out the coordinate data in accordance with a predetermined thinning-out condition, and thus generates the stroke data such that an increase in the amount of data is suppressed. The CPU  21  stores the data that is acquired in the course of the processing in the RAM  22 , as appropriate. 
     As shown in  FIG. 3 , the CPU  21  performs initialization in the main processing. The CPU  21  secures a storage area for the stroke data in the flash ROM  23 , and sets an area to which the stroke header is added. The CPU  21  acquires time information from a clock (not shown in the drawings) and stores the time information in the stroke header. The CPU  21  secures storage areas for variables [LastPoint] and [NowPoint] in the RAM  22 , and sets a default value (NULL, NULL) as [LastPoint] (step S 11 , refer to a reference symbol A in  FIG. 4 ). The CPU  21  determines whether or not the pen down signal is received from one of the ASIC  28 A and the ASIC  29 A (step S 13 ). In a case where the pen down signal is not received from one of the ASIC  28 A and the ASIC  29 A (no at step S 13 ), the CPU  21  determines that information is not written using the electronic pen  3  and returns the processing to step S 11 . Until information is written on the paper medium  100  using the electronic pen  3 , the CPU  21  repeats the processing at step S 11  and step S 13 . In a case where the pen down signal is received from one of the ASIC  28 A and the ASIC  29 A (yes at step S 13 ), the CPU  21  acquires the coordinate data output by one of the ASIC  28 A and the ASIC  29 A (step S 15 ). The CPU  21  stores the acquired coordinate data in [NowPoint] (step S 17 , refer to an arrow B in  FIG. 4 ). 
     The CPU  21  determines whether or not the acquired coordinate data satisfies the thinning-out condition (step S 19 ). In the present embodiment, the condition that [NowPoint] and [LastPoint] are the same coordinate data is set in advance as the thinning-out condition. The CPU  21  compares [NowPoint] and [LastPoint]. In a case where the coordinate data of [NowPoint] is not the same as the coordinate data of [LastPoint], the thinning-out condition is not satisfied (no at step S 19 ). In this case, the CPU  21  adds the coordinate data of [NowPoint] to the end of the stroke data secured in the flash ROM  23 , and stores the added coordinate data (step S 23 ) (refer to an arrow C in  FIG. 4 ). The CPU  21  copies the coordinate data of [NowPoint], and sets the copied coordinate data as the coordinate data of [LastPoint] (step S 25 ) (refer to an arrow D in  FIG. 4 ), and returns the processing to step S 13 . Although not shown in the drawings, before the CPU  21  returns the processing to step S 13  after performing the processing at step S 25 , the CPU  21  waits until a predetermined time period has elapsed, so that the acquisition of the coordinate data at step S 15  is performed periodically. 
     The CPU  21  repeats the processing at step S 13  to step S 25  while the same coordinate data is not consecutively acquired, that is, repeats the processing that adds the acquired coordinate data to the stroke data (refer to an arrow E in  FIG. 4 ) and sets the acquired coordinate data as the coordinate data of [LastPoint] (refer to an arrow F in  FIG. 4 ). In a case where the same coordinate data (refer to a reference symbol G in  FIG. 4 ) is consecutively acquired, the coordinate data of [NowPoint] and the coordinate data of [LastPoint] are the same and the thinning-out condition is satisfied (yes at step S 19 ). In this case, the CPU  21  determines whether or not the pen up signal is received (step S 31 ). In a case where the user is continuing to write information, the CPU  21  does not receive the pen up signal (no at step S 31 ). In this case, the CPU  21  returns the processing to step S 15 . Therefore, in this round of the processing, the coordinate data (refer to a reference symbol H in  FIG. 4 ) that is stored in [NowPoint] is not added to the stroke data and is thinned out. Although not shown in the drawings, in a similar manner to when the CPU  21  returns the processing to step S 13  after performing the processing at step S 25 , if the pen up signal is not received in the processing at step S 31  (no at step S 31 ), the CPU  21  waits until a predetermined time period elapses before the CPU  21  returns the processing to step S 15 , so that the acquisition of the coordinate data at step S 15  is performed periodically. 
     After that, in a similar manner to that described above, while the same coordinate data as the coordinate data of [LastPoint] is consecutively acquired (step S 15 , step S 17 , yes at step S 19 , no at step S 31 ) (refer to a reference symbol I in  FIG. 4 ), the CPU  21  thins out the acquired coordinate data and does not add the acquired coordinate data to the stroke data. In a case where the CPU  21  acquires coordinate data that is different from the coordinate data of [LastPoint] (no at step S 19 ) (refer to a reference symbol J in  FIG. 4 ), the CPU  21  adds the acquired coordinate data to the stroke data (step S 23 ) (refer to a reference symbol K in  FIG. 4 ), and sets the acquired coordinate data as the coordinate data of [LastPoint] (step S 25 ) (refer to a reference symbol L in  FIG. 4 ). 
     After the CPU  21  performs the processing that generates the stroke data, if the pen up signal is received from the ASIC  28 A and the ASIC  29 A (no at step S 13 ), the CPU  21  completes the generation of the stroke data and returns the processing to step S 11 . The CPU  21  counts up the number of the pieces of coordinate data added to the stroke data, and stores the number in the stroke header as the data piece number information. The CPU  21  secures a new storage area for the stroke data in the flash ROM  23 , and sets an area to which the stroke header is added. Then, the CPU  21  repeats the processing at step S 11  and step S 13  until information is newly written on the paper medium  100  using the electronic pen  3 . 
     After the CPU  21  determines at step S 19  that the acquired coordinate data satisfies the thinning-out condition (yes at step S 19 ), if the pen up signal is received from the ASIC  28 A and the ASIC  29 A (yes at step S 31 ), the CPU  21  advances the processing to step S 33 . The CPU  21  adds the coordinate data stored in [NowPoint] by the processing at step S 17  to the end of the stroke data secured in the flash ROM  23 , and stores the added coordinate data (step S 33 ). More specifically, when the CPU  21  acquires the same coordinate data (yes at step S 19 ) and thins out the coordinate data, if the user ends the writing of information on the paper medium  100  and separates the electronic pen  3  from the paper medium  100  (yes at step S 31 ), the CPU  21  adds the latest acquired coordinate data (the coordinate data acquired immediately before the pen up) to the stroke data (step S 33 ), and completes the generation of the stroke data. The CPU  21  returns the processing to step S 11  and stands by until information is newly written on the paper medium  100  using the electronic pen  3  (step S 11 , no at step S 13 ). 
     As explained above, in a case where the coordinate data that is the same as the coordinate data of [LastPoint] is acquired, the information input device  1  of the present embodiment does not add the acquired coordinate data to the stroke data and thins out the acquired coordinate data. Therefore, the information input device  1  can suppress the increase in the amount of information of the stroke data. It is thus possible to reduce the area of the flash ROM  23  in which the stroke data is stored. Further, in a case where the stroke data is used on a PC or the like, it is possible to reduce a time period required to transmit the stroke data from the information input device  1  to the PC or the like. 
     At step S 19 , the CPU  21  can perform the determination processing as to whether or not the thinning-out condition is satisfied, by determining whether or not the coordinate data of [LastPoint] is the same as the coordinate data of [NowPoint]. Therefore, the information input device  1  can reduce a load involved in the determination processing, and can rapidly determine whether or not the acquired coordinate data is to be added to the stroke data. 
     Various modifications can be made to the above-described embodiment. In the above-described embodiment, the condition that the coordinate data of [Nowpoint] is the same as the coordinate data of [Lastpoint] is set as the thinning-out condition, and at step S 19  of the main processing, the CPU  21  determines whether or not the thinning-out condition is satisfied. For example, a condition that the distance between the position indicated by the coordinate data of [NowPoint] and the position indicated by the coordinate data of [LastPoint] is less than a predetermined distance may be set as the thinning-out condition. The operation of the main processing that is performed in this case will be explained as a first modified example with reference to  FIG. 3  and  FIG. 5 . 
     As shown in  FIG. 3  and  FIG. 5 , in a case where the CPU  21  receives the pen down signal during standby (yes at step S 13 ), the CPU  21  acquires coordinate data P 1  (refer to  FIG. 5 ) from one of the ASIC  28 A and the ASIC  29 A (step S 15 ), and stores the coordinate data P 1  in [NowPoint] (step S 17 ). The CPU  21  calculates a distance between the position indicated by the coordinate data of [NowPoint] and the position indicated by the coordinate data of [LastPoint], and determines whether or not the calculated distance is less than a predetermined distance R (step S 19 ). Immediately after the CPU  21  has received the pen down signal, (NULL, NULL) is set as [LastPoint]. Therefore, the CPU  21  determines that the calculation of the distance is not valid, and determines that the thinning-out condition is not satisfied (no at step S 19 ). Therefore, the CPU  21  adds the coordinate data P 1  to the stroke data (step S 23 ), and sets the coordinate data P 1  as the coordinate data of [LastPoint] (step S 25 ). 
     The CPU  21  acquires next coordinate data P 2  and stores the coordinate data P 2  in [NowPoint] (step S 15 , step S 17 ). The CPU  21  determines whether or not a distance between the position indicated by the coordinate data of [NowPoint] and the position indicated by the coordinate data P 1  of [LastPoint] is less than the predetermined distance R. More specifically, the CPU  21  determines whether or not the coordinates indicated by the coordinate data P 2  are included within a virtual circle Q, which is centered on the coordinates indicated by the coordinate data P 1  and whose radius is the predetermined distance R. The predetermined distance R is, for example, 5 dots when each coordinate set is represented by a dot. The coordinates indicated by the coordinate data P 2  are proximate coordinates whose distance from the coordinates indicated by the coordinate data P 1  is less than the predetermined distance R (yes at step S 19 ). In this case, the CPU  21  does not add the coordinate data P 2  to the stroke data and acquires next coordinate data P 3 . The CPU  21  does not add the coordinate data P 3  that satisfies the thinning-out condition to the stroke data, and acquires next coordinate data P 4  (no at step S 31 , step S 15 ). The CPU  21  stores the newly acquired coordinate data P 4  in [NowPoint] (step S 17 ). The CPU  21  calculates a distance between the position indicated by the coordinate data P 4  of [NowPoint] and the position indicated by the coordinate data P 1  of [LastPoint]. In a case where the calculated distance is equal to or more than the predetermined distance R and the thinning-out condition is not satisfied (no at step S 19 ), the CPU  21  adds the coordinate data P 4  to the stroke data (step S 23 ), and sets the coordinate data P 4  as the coordinate data of [LastPoint]. 
     After that, in a similar manner to that described above, the CPU  21  does not add coordinate data P 5 , P 6 , P 8 , P 9 , and P 11  to the stroke data and thins them out. The coordinate data P 5 , P 6 , P 8 , P 9 , and P 11  each indicate a position whose distance from the position indicated by the coordinate data of [LastPoint] is less than the predetermined distance R. The CPU  21  adds coordinate data P 7  and P 10  to the stroke data and sets each of the coordinate data P 7  and P 10  as a new [LastPoint]. The coordinate data P 7  and P 10  each indicate a position whose distance from the position indicated by the coordinate data of [LastPoint] is equal to or more than the predetermined distance R. The CPU  21  acquires coordinate data P 12 , which indicates a position whose distance from the position indicated by the coordinate data P 10  of [LastPoint] is less than the predetermined distance R, and which satisfies the thinning-out condition (yes at step S 19 ). After that, if the pen up signal is received (yes at step S 31 ), the CPU  21  does not thin out the coordinate data P 12  and adds the coordinate data P 12  to the stroke data (step S 33 ). 
     As described above, in the first modified example, the thinning-out condition is that the distance between the position indicated by the coordinate data of [NowPoint] and the position indicated by the coordinate data of [LastPoint] is less than a predetermined distance. In other words, the CPU  21  can thin out the acquired coordinate data without adding the acquired coordinate data to the stroke data not only when the coordinates indicated by the acquired coordinate data are the same as the coordinates indicated by the coordinate data of [LastPoint], but also when the coordinates indicated by the acquired coordinate data are coordinates in the vicinity of the coordinates indicated by the coordinate data of [LastPoint]. Therefore, the information input device  1  can further suppress the increase in the amount of information of the stroke data. 
     In the above-described embodiment, in a case where the CPU  21  consecutively acquires the coordinate data that is the same as the coordinate data of [LastPoint], the CPU  21  thins out the same coordinate data and generates the stroke data. In a case where the CPU  21  consecutively acquires the coordinate data that is the same as the coordinate data of [LastPoint], the CPU  21  may add, to the stroke data, the coordinate data that is acquired once in a predetermined number of times N. The operation of the main processing that is performed in this case will be explained as a second modified example with reference to  FIG. 6 . In  FIG. 6 , processing that is the same as the processing in the main processing of the present embodiment explained with reference to  FIG. 3  is denoted by the same step number and an explanation thereof is simplified. 
     As shown in  FIG. 6 , the CPU  21  performs the initialization in the main processing, and secures a storage area for the stroke data in the flash ROM  23 , and secures storage areas for the variables [LastPoint] and [NowPoint] and a counter [repeat] in the RAM  22 . The CPU  21  sets the default value (NULL, NULL) as [LastPoint] and sets 0 as [repeat] (step S 12 ). Then, in the same manner as in the above-described embodiment, the CPU  21  repeats the processing at step S 12  and step S 13  until information is written on the paper medium  100  using the electronic pen  3 . 
     In a case where the pen down signal is received from one of the ASIC  28 A and the ASIC  29 A (yes at step S 13 ), the CPU  21  acquires coordinate data (step S 15 ) and stores the acquired coordinate data in [NowPoint] (step S 17 ). In a case where the coordinate data of [NowPoint] is not the same as the coordinate data of [LastPoint] and the thinning-out condition is not satisfied (no at step S 19 ), the CPU  21  sets 0 as [repeat] (step S 21 ). The CPU  21  adds the coordinate data of [NowPoint] to the stroke data (step S 23 ). The CPU  21  sets the coordinate data of [NowPoint] as the coordinate data of [LastPoint] (step S 25 ) and returns the processing to step S 13 . 
     While the same coordinate data is consecutively not acquired, the CPU  21  repeats the processing at step S 13  to step S 25 , and repeats the processing that adds the acquired coordinate data to the stroke data and then sets the acquired coordinate data as the coordinate data of [LastPoint]. In a case where the same coordinate data is consecutively acquired, the coordinate data of [NowPoint] and the coordinate data of [LastPoint] are the same and the thinning-out condition is satisfied (yes at step S 19 ). In this case, the CPU  21  increments [repeat] by adding 1 to [repeat] (step S 27 ). In a case where [repeat] is not equal to or more than the predetermined number of times N (no at step S 29 ) and the pen up signal is not received (no at step S 31 ), the CPU  21  returns the processing to step S 15 . Therefore, in this round of the processing, the coordinate data stored in [NowPoint] is not added to the stroke data and is thinned out. 
     While the coordinate data that is the same as the coordinate data of [LastPoint] is consecutively acquired, the CPU  21  increments [repeat] (step S 27 ) and thins out the acquired coordinate data. In a case where [repeat] reaches the predetermined number of times N (three, for example) (yes at step S 29 ), the CPU  21  returns the processing to step S 21 . The CPU  21  resets [repeat] to 0 (step S 21 ), adds the coordinate data of [NowPoint] to the stroke data (step S 23 ), and then sets the coordinate data of [NowPoint] as the coordinate data of [LastPoint] (step S 25 ). Then, in the same manner as described above, while the coordinate data that is the same as the coordinate data of [LastPoint] is consecutively acquired, the CPU  21  increments [repeat] and thins out the acquired coordinate data. 
     After the CPU  21  performs the processing that generates the stroke data, if the pen up signal is received (no at step S 13 ), the CPU  21  ends the generation of the stroke data and returns the processing to step S 12 . The CPU  21  secures a new storage area for the stroke data. Until information is newly written on the paper medium  100  using the electronic pen  3 , the CPU  21  repeats the processing at step S 12  and step S 13 . After the CPU  21  thins out the coordinate data, if the pen up signal is received (yes at step S 31 ), the CPU  21  adds the coordinate data stored in [NowPoint] in the processing at step S 17  to the end of the stroke data, and stores the added coordinate data (step S 33 ). The CPU  21  completes the generation of the stroke data and returns the processing to step S 12 . 
     As described above, in the second modified example, in a case where the coordinate data that satisfies the thinning-out condition is consecutively acquired, the CPU  21  can add, to the stroke data, the coordinate data that is acquired once in the predetermined number of times N, without thinning out the acquired coordinate data. Therefore, the information input device  1  can secure accuracy of information while suppressing the increase in the amount of information of the stroke data. 
     In a similar manner to the first modified example, also in the second modified example, the thinning-out condition may be, for example, the condition that the distance between the position indicated by the coordinate data of [NowPoint] and the position indicated by the coordinate data of [LastPoint] is less than a predetermined distance. In a case where this type of thinning-out condition is set in the second modified example, the information input device  1  can secure accuracy of information while further suppressing the increase in the amount of information of the stroke data. 
     The information input device  1  may use a resistive membrane method (a so-called pressure-sensitive method), an electrostatic capacitance method, or another method to detect the electronic pen  3  that is in contact with or is close to the housings  8 L and  8 R that house the sensor boards  71  and  72 . The size, the format, the material and the like of the paper medium  100  are not limited to those of the above-described embodiment. 
     The ASIC  28 A and the ASIC  29 A may convert the electric current that flows through the loop coils of each of the sensor boards  71  and  72  into a voltage value. Then, the ASIC  28 A and the ASIC  29 A may perform analog/digital conversion of the obtained voltage value and output the converted voltage value to the CPU  21 . The CPU  21  may generate the coordinate data based on the voltage value obtained from each of the ASIC  28 A and the ASIC  29 A. 
     The apparatus and methods described above with reference to the various embodiments are merely examples. It goes without saying that they are not confined to the depicted embodiments. While various features have been described in conjunction with the examples outlined above, various alternatives, modifications, variations, and/or improvements of those features and/or examples may be possible. Accordingly, the examples, as set forth above, are intended to be illustrative. Various changes may be made without departing from the broad spirit and scope of the underlying principles.