US20130035890A1

US20130035890A1 - Moving trajectory calibration method and moving trajectory generation method

Info

Publication number: US20130035890A1
Application number: US13/566,651
Authority: US
Inventors: Jeen-Shing WANG; Yu-Liang Hsu
Original assignee: Individual
Current assignee: National Cheng Kung University NCKU
Priority date: 2011-08-04
Filing date: 2012-08-03
Publication date: 2013-02-07
Also published as: US9098123B2; US20130069917A1; TW201308128A; TW201308218A; TWI474265B; CN102915130B; CN102915171A; TWI512548B; CN102915130A

Abstract

A moving trajectory calibration method is applied to receive a moving trajectory signal generated by a writing device while moving on a written plane and includes the following steps of: generating a first axial signal, a second axial signal and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane; calibrating the first axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal; and calibrating the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a second axial trajectory signal. In addition, a moving trajectory generation method is also disclosed.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The non-provisional patent application claims priority to U.S. provisional patent application with Ser. No. 61/514,960 filed on Aug. 4, 2011. This and all other extrinsic materials discussed herein are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention
The present invention relates to a moving trajectory calibration method and a moving trajectory generation method.
2. Related Art
Recently, tremendous progress in miniaturization technology in electronic circuits and components has greatly decreased the dimension and weight of consumer electronic products and make them extremely powerful, portable, and convenient. Due to the rapid development of computer technology, human-computer interaction (HCI) techniques have become one of the indispensable tools in our daily life. In particularly, the hand writing through the HCI is an essential recording or expressing method. Today, many handwriting-based HCI sensing technologies, which mainly include the electromagnetic, electric, ultrasonic, pressure, and optical sensing technologies, have been disclosed.
However, the electromagnetic HCI sensing technology needs a battery with larger capacity to provide a large power for generating the electromagnetic field so as to detect and position the writing position, which is the pen-point of the writing device. Thus, this type writing device becomes heavier and is inconvenient in carrying. Besides, the electric HCI sensing technology needs to cooperate with a specific electrode paper and use the transmission and receiving electrodes of the electrode paper to detect the moving trajectory of the writing device. Unfortunately, the electrode paper is very expensive, so this electric HCI sensing technology can not be popularized. The ultrasonic HCI sensing technology utilizes the arrival-time difference between the ultrasonic signals and the triangulation location method to calculate the writing trajectory coordinates of the pen-point of the writing device. Although the ultrasonic HCI sensing technology can precisely capture the moving trajectory of the writing device on any 2-dimensional plane, the writing range for receiving the ultrasonic waves with the cooperated receiving device is limited and very inconvenient. The pressure HCI sensing technology has a limited writing range within the area of the pressure sensing electronic board, so its operation is also inconvenient. The optical HCI sensing technology utilizes the optical sensor of the optical mouse to sense the moving trajectory of the writing device on a written plane. The sensing theory is similar to that of the optical mouse, so that it is possible to simply convert the moving trajectory information into the operation signal of the cursor without developing additional application programming interface (API) software.
However, in all of the above sensing technologies, when writing device leaves the 2-dimensional written plane as it is lifted up or moved to next stroke, the sensing devices still output the unnecessary sensing signals to generate the incorrect moving trajectory.
Therefore, it is an important subject of the present invention to provide a moving trajectory calibration method and a moving trajectory generation method that can correct the distorted moving trajectory as the writing device is lifted up or moved to next stroke so as to obtain the correct moving trajectory.

SUMMARY OF THE INVENTION

In view of the foregoing subject, an objective of the present invention is to provide a moving trajectory calibration method and a moving trajectory generation method that can detect handwriting signals and correct the distorted moving trajectory as the writing device is lifted up or moved to next stroke so as to obtain the correct moving trajectory.
To achieve the above objective, the present invention discloses a moving trajectory calibration method, which is applied to receive a moving trajectory signal generated by a writing device while moving on a written plane. The calibration method comprises the steps of: generating a first axial signal, a second axial signal and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane; calibrating the first axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal; and calibrating the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a second axial trajectory signal.
In one embodiment, the moving trajectory signal comprises an angular velocity signal, an acceleration signal, a magnetic-field intensity signal, a geomagnetic orientation signal, or their combinations in three axes with respect to a moving trajectory at different time points.
In one embodiment, the first axis, the second axis and the third axis are perpendicular to one another.
In one embodiment, the step of calibrating the first axial signal further comprises: when a variation of the third axial signal within a time interval exceeds a preset signal value, the detecting-calibration unit zeros the first axial signal within the time interval.
In one embodiment, the step of calibrating the second axial signal further comprises: when a variation of the third axial signal within a time interval exceeds a preset signal value, the detecting-calibration unit zeros the second axial signal within the time interval.
To achieve the above objective, the present invention also discloses a moving trajectory generation method, comprising the steps of: sensing a moving trajectory while a writing device moves on a written plane by a moving trajectory sensing module of the writing device, and generating a moving trajectory signal; generating a first axial signal, a second axial signal and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane; calibrating the first axial signal and the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal and a second axial trajectory signal, respectively; and displaying the calibrated moving trajectory by a display module according to the first axial trajectory signal and the second axial trajectory signal.
In one embodiment, the moving trajectory generation method further comprises the step of: generating a coordinate transformation matrix according to the angular velocity signals by an orientation transformation unit of the orientation calculation module, and performing the coordinate transformation to the acceleration signals according to the coordinate transformation matrix.
In one embodiment, the orientation transformation unit integrates the angular velocity signals to obtain an orientation angle so as to generate the coordinate transformation matrix, and transforms the acceleration signals with the coordinate transformation matrix so as to transform the acceleration signals from a body frame of the writing device to a local level frame.
In one embodiment, the moving trajectory generation method further comprises the step of: performing a gravity compensation to the acceleration signals in the local level frame by a gravity compensation unit of the orientation calculation module.
In one embodiment, the moving trajectory generation method further comprises the step of: performing a calculation to the first axial trajectory signal and the second axial trajectory signal by a trajectory calculation unit of the orientation calculation module.
In one embodiment, the written plane comprises a horizontal plane, a vertical plane, or a slant plane.
As mentioned above, in the moving trajectory calibration method and moving trajectory generation method of the invention, a detecting-calibration unit of an orientation calculation module generates a first axial signal, a second axial signal and a third axial signal according to the moving trajectory signal, while the written plane is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane. In addition, the detecting-calibration unit calibrates the first axial signal and the second axial signal according to the third axial signal so as to generate a first axial trajectory signal and a second axial trajectory signal, respectively, and the display module then displays the calibrated moving trajectory according to the first axial trajectory signal and the second axial trajectory signal. Accordingly, the moving trajectory calibration method and moving trajectory generation method of the invention can detect handwriting signals and correct the distorted moving trajectory as the writing device is lifted up or moved to next stroke so as to obtain the correct moving trajectory.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detailed description and accompanying drawings, which are given for illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1A is a schematic diagram showing the circumstance of using a writing device to write on a written plane;

FIG. 1B is a block diagram of the writing device of FIG. 1A;

FIG. 1C is a flow chart of a moving trajectory calibration method according to a preferred embodiment of the invention;

FIG. 2A is a schematic diagram showing the moving trajectory as using the writing device to write “4”;

FIG. 2B is a schematic diagram showing a modified moving trajectory by applying the moving trajectory generation method of the invention to the moving trajectory of FIG. 2A;

FIG. 3A is a waveform diagram showing the acceleration signals in three axes from the moving trajectory signal;

FIG. 3B is a waveform diagram showing the acceleration signals in three axes of FIG. 3A processed by a coordinate transformation;

FIG. 3C is a waveform diagram showing the acceleration signals in three axes of FIG. 3B processed by a gravity compensation;

FIGS. 4A to 4C are waveform diagrams of a first axial signal, a second axial signal, and a third axial signal, respectively;

FIG. 5A is a flow chart of a moving trajectory generation method according to a preferred embodiment of the invention;

FIG. 5B is a block diagram of the writing device applied to the moving trajectory generation method of FIG. 5A;

FIG. 6A is a schematic diagram showing the moving trajectory as using the writing device to write “12”;

FIG. 6B is a schematic diagram showing a modified moving trajectory by applying the moving trajectory generation method of the invention to the moving trajectory of FIG. 6A;

FIG. 7A is a schematic diagram showing the moving trajectory as using the writing device to write “86”; and

FIG. 7B is a schematic diagram showing a modified moving trajectory by applying the moving trajectory generation method of the invention to the moving trajectory of FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.
FIG. 1A is a schematic diagram showing the circumstance of using a writing device 1 to write on a written plane P, and FIG. 1B is a block diagram of the writing device 1.
The writing device 1 includes an inertia sensing element for sensing the angle, orientation, and displacement of the writing device 1 in the 3-dimensional space. In this case, the shape of the writing device 1 is a pen. Otherwise, the writing device can be made of other shapes or types such as a mouse.
Referring to FIG. 1B, the writing device 1 includes a moving trajectory sensing module. In addition, the writing device 1 may further include an orientation calculation module. In other embodiments, another processing device, such as a computer, may also include the orientation calculation module, and the signals generated by the moving trajectory sensing module can be transmitted to the orientation calculation module by wires or wireless for further calculation.
The moving trajectory sensing module can sense a moving trajectory, which is generated as the writing device 1 moves in the 3-dimensional space, and generate a moving trajectory signal in real time. The moving trajectory sensing module includes a multi-axis dynamic switch. The moving trajectory can be a trajectory of a digit, a letter, a symbol, a line or any writing trajectory. In addition, the moving trajectory signal may include the coordinate information, angular velocity information, gravity information, acceleration information, magnetic-field intensity information, geomagnetic orientation information, any other information, or their combinations in three axes with respect to a moving trajectory at different time points. Besides, the written plane P may comprise a horizontal plane, a vertical plane, or a slant plane. In this embodiment, the written plane P is a horizontal plane.
The moving trajectory sensing module includes, for example, a gyroscope, an accelerometer, a magnetometer or an electronic compass, or their combinations. These devices can be a single axis or multiple axes (e.g. three axes), and the moving trajectory signal includes an angular velocity signal, an acceleration signal, a magnetic-field intensity signal, a geomagnetic orientation signal, or their combinations in three axes with respect to a moving trajectory at different time points. In this embodiment, the moving trajectory sensing module includes a triaxial gyroscope and a triaxial accelerometer for measuring the triaxial angular velocity signals, the gravity g, and the triaxial acceleration signals. To be noted, the writing device 1 or another processing device may further include a calibration filtering unit (not shown), which can calibrate the signal generated by the inertia element of the moving trajectory sensing module, such as the above-mentioned gyroscope, accelerometer, magnetometer or electronic compass, or their combinations, and filter the noise of the inertia element or the contaminated moving trajectory signal caused by unintentional hand motion (e.g. hand trembles) or other environmental interference.
Before performing the steps of the moving trajectory calibration method of the embodiment, the moving trajectory signal (e.g. angular velocity signals and the acceleration signals) must be preprocessed. As shown in FIG. 1B, the triaxial angular velocity signals are integrated by an orientation transformation unit of the orientation calculation module so as to obtain an orientation angle of the writing device 1. Herein, the orientation angle includes the roll angle Φ, the pitch angle θ, and the yaw angle φ. The major function of the orientation angle is to provide the relative angle or rotation relationship between the body frame of the writing device 1 and local level frame.
The roll angle Φ represents an angle that the writing device 1 rotates along a first axis of the body frame, which can be obtained by integrating the angular velocity of the writing device 1 in the first direction. In other aspects, the roll angle Φ also represents an angle that the writing device 1 rotates along the first direction, which can be obtained according to the components of gravity measured by the accelerometer of the writing device 1 in triaxial directions. In addition, the pitch angle θ represents an angle that the writing device 1 rotates along a second axis of the body frame which can be obtained by integrating the angular velocity of the writing device 1 in the second direction. In other aspects, the pitch angle θ also represents an angle that the writing device 1 rotates along the second direction, which can be obtained according to the components of gravity measured by the accelerometer of the writing device 1 in triaxial directions. The yaw angle φ represents an angle that the writing device 1 rotates along a third axis of the body frame which can be obtained by integrating the angular velocity of the writing device 1 in the third direction. In other aspects, the yaw angle φ also represents an angle that the writing device 1 rotates along the third direction, which can be obtained according to the magnetic-field intensity measured by the magnetometer of the writing device 1, or by the geomagnetic orientation measured by the electronic compass. Otherwise, the roll angle, pitch angle, and yaw angle can also be obtained according to, for example but not limited to, the magnetic-field intensity, geomagnetic orientation, or their combinations of the writing device 1.
Afterwards, the orientation transformation unit generates a coordinate transformation matrix according to the angular velocity signal and its orientation angle, so that the acceleration signals in three axes generated by the moving trajectory sensing module can be transformed from the body frame of the writing device 1 to the local level frame by the coordinate transformation matrix. In addition, a gravity compensation unit of the orientation calculation module performs a gravity compensation to the acceleration signal so as to eliminate the acceleration variation caused by gravity. Then, a detecting-calibration unit of the orientation calculation module calibrates the moving trajectory. To be noted, the above-mentioned coordinate transformation and gravity compensation are well known by those who skilled in the art, so their detailed descriptions will be omitted.
With reference to FIG. 2A, for example, the user operates the writing device 1 to write a number “4”. A part of the moving trajectory from the position A to the position B of FIG. 2A is generated as the writing device 1 is lifted up and moved. In this case, the moving trajectory calibration method of the invention can perform a trajectory calibration so as to eliminate the part of the moving trajectory generated as the writing device 1 is lifted up and moved (from the position A to the position B), thereby obtaining the correct moving trajectory of the number “4” as shown in FIG. 2B.
FIG. 1C is a flow chart of a moving trajectory calibration method according to a preferred embodiment of the invention.
Referring to FIGS. 1B and 1C, the moving trajectory calibration method is applied to receive a moving trajectory signal generated by a writing device 1 while moving on a written plane P. The preprocessing procedure of the moving trajectory signal has been described hereinabove, so the detailed description thereof will be omitted.
FIG. 3A is a waveform diagram showing the acceleration signals in the first axis X, the second axis Y, and the third axis Z of the body frame, which are obtained from the moving trajectory signal outputted by the moving trajectory sensing module and preprocessed, for example, by calibration and filtering. FIG. 3B is a waveform diagram showing the acceleration signals in three axes of FIG. 3A processed by a coordinate transformation, wherein the acceleration signals are transformed from the body frame to the local level frame. As shown in FIG. 3B, the basic level in the third axis Z is 1 g, and the basic levels in the first axis X and the second axis Y are 0 g. In addition, FIG. 3C is a waveform diagram showing the acceleration signals in three axes of FIG. 3B processed by a gravity compensation. As shown in FIG. 3C, the gravity compensation unit can perform a proper compensation to the acceleration signals of the local level frame so as to eliminate the interference of the acceleration caused by gravity. Referring to FIG. 3C, the basic level in the first axis X, the second axis Y, and the third axis Z are 0 g.
FIG. 1C is a flow chart of a moving trajectory calibration method according to a preferred embodiment of the invention, wherein the moving trajectory calibration method include the following steps P01 to P03.
First, the step P01 is to generate a first axial signal, a second axial signal and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane P is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane P. In this embodiment, the first axis, the second axis, and the third axis are three axes of the local level frame, which are perpendicular to each other (the axes X, Y and Z of FIG. 2A). The written plane P is composed of the first axis X and the second axis Y, and the third axis Z is perpendicular to the written plane P. The first axial signal, the second axial signal, and the third axial signal (acceleration signals) are shown in FIGS. 4A to 4C, respectively. In other embodiments, when the written plane is a vertical plane, such as the plane composed of the axis X and axis Z of FIG. 2A, the third axis is the axis Y.
Next, the step P02 is to calibrate the first axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal. In this embodiment, the third axial signal is caused by the motion of lifting up the writing device and moving the writing device to next stroke, so that it can be used to calibrate the first axial signal and the second axial signal. In addition, the step P02 of calibrating the first axial signal further includes: when a variation of the third axial signal within a time interval exceeds a preset signal value, the detecting-calibration unit zeros the first axial signal within the time interval. In other words, it is determined that the third axial signal is caused by the motion of lifting up the writing device and moving the writing device to next stroke, so that the third axial signal is unnecessary. In more detailed, when the variation of the third axial signal within a time interval (between t1 and t2 of FIG. 4C) exceeds the preset signal value, it is determined that the third axial signal is caused by the motion of lifting up the writing device and moving the writing device to next stroke. Thus, the signal in the first axis X within this time interval must be eliminated, which is to zero the first axial signal within this time interval. FIG. 4A shows the first axial signal within this time interval but does not show that the first axial signal is zeroed within this time interval. Herein, the preset signal value can be defined by the user.
Finally, the step P03 is to calibrate the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a second axial trajectory signal. Similarly, when a variation of the third axial signal within a time interval exceeds a preset signal value, the detecting-calibration unit zeros the second axial signal within the time interval. Thus, the signal in the second axis Y within this time interval must be eliminated too, which is to zero the second axial signal within this time interval. FIG. 4B shows the second axial signal within this time interval but does not show that the second axial signal is zeroed within this time interval. To be noted, the above order of the steps P02 and P03 is for illustration only and is not to limit the present invention. It is possible to perform the step P03 before the step P02, or to perform the steps P02 and P03 at the same time.
FIG. 5A is a flow chart of a moving trajectory generation method according to a preferred embodiment of the invention, and FIG. 5B is a block diagram of the writing device applied to the moving trajectory generation method of FIG. 5A.
Referring to FIGS. 5A and 5B, the moving trajectory generation method comprises the steps of: sensing a moving trajectory while a writing device 1 moves on a written plane P by a moving trajectory sensing module of the writing device 1, and generating a moving trajectory signal (step S01); generating a first axial signal, a second axial signal, and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane P is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane P (step S02); and calibrating the first axial signal and the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal and a second axial trajectory signal (step S03). The step S01 has been described hereinabove and the steps S02 and S03 can be referred to the above steps P01 to P03, so their detailed descriptions will be omitted.
In addition, the moving trajectory generation method may further comprise a step of: displaying the calibrated moving trajectory by a display module according to the first axial trajectory signal and the second axial trajectory signal (step S04). In other words, as shown in FIG. 2B, a monitor of a computer can display the calibrated correct moving trajectory. In this embodiment, as shown in FIG. 2B, the acceleration signal in the third axis Z caused by the motion of lifting up the writing device or moving the writing device to next stroke is removed from the first axial signal and the second axial signal, so that the display module can display the calibrated moving trajectory according to the first axial trajectory signal and the second axial trajectory signal. To be noted, before the step S04, the moving trajectory generation method further comprises the step of: performing a calculation to the first axial trajectory signal and the second axial trajectory signal by a trajectory calculation unit of the orientation calculation module (see FIG. 5B). In this step S04, the calibrated acceleration signals in the first axis and the second axis are integrated twice to generate a displacement signal, and then the displacement signal is transformed to the moving trajectory which is displayed by the display module.
The other technical features of the moving trajectory generation method have been described in the above description, so they will be omitted here.
FIG. 6A is a schematic diagram showing the moving trajectory as using the writing device 1 to write “12”, and FIG. 6B is a schematic diagram showing a modified moving trajectory by applying the moving trajectory generation method of the invention to the moving trajectory of FIG. 6A, which is displayed by the display module. FIG. 7A is a schematic diagram showing the moving trajectory as using the writing device 1 to write “86”, and FIG. 7B is a schematic diagram showing a modified moving trajectory by applying the moving trajectory generation method of the invention to the moving trajectory of FIG. 7A, which is displayed by the display module.
As shown in FIGS. 6A and 7A, a part of the moving trajectory between the positions A and B is caused by the motion of lifting up the writing device or moving the writing device to next stroke. Accordingly, as shown in FIGS. 6B and 7B, the moving trajectory generation method of the invention can detect handwriting signals and correct the distorted moving trajectory caused by the motion of lifting up the writing device or moving the writing device to next stroke, thereby obtaining the correct moving trajectory.
To sum up, in the moving trajectory calibration method and moving trajectory generation method of the invention, a detecting-calibration unit of an orientation calculation module generates a first axial signal, a second axial signal, and a third axial signal according to the moving trajectory signal, while the written plane is composed of the first axis and the second axis, and the third axis is perpendicular to the written plane. In addition, the detecting-calibration unit calibrates the first axial signal and the second axial signal according to the third axial signal so as to generate a first axial trajectory signal and a second axial trajectory signal, respectively, and the display module then displays the calibrated moving trajectory according to the first axial trajectory signal and the second axial trajectory signal. Accordingly, the moving trajectory calibration method and moving trajectory generation method of the invention can detect handwriting signals and correct the distorted moving trajectory as the writing device is lifted up or moved to next stroke so as to obtain the correct moving trajectory.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.

Claims

1. A moving trajectory calibration method, which is applied to receive a moving trajectory signal generated by a writing device while moving on a written plane, the calibration method comprising the steps of:

generating a first axial signal, a second axial signal, and a third axial signal according to the moving trajectory signal by a detecting-calibration unit of an orientation calculation module, wherein the written plane is composed of a first axis and a second axis, and a third axis is perpendicular to the written plane;

calibrating the first axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal; and

calibrating the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a second axial trajectory signal.

2. The calibration method of claim 1, wherein the moving trajectory signal comprises an angular velocity signal, an acceleration signal, a magnetic-field intensity signal, a geomagnetic orientation signal, or their combinations in three axes with respect to a moving trajectory at different time points.

3. The calibration method of claim 1, wherein the first axis, the second axis, and the third axis are perpendicular to one another.

4. The calibration method of claim 1, wherein the step of calibrating the first axial signal further comprises:

when a variation of the third axial signal within a time interval exceeds a preset signal value, the detecting-calibration unit zeros the first axial signal within the time interval.

5. The calibration method of claim 1, wherein the step of calibrating the second axial signal further comprises:

when a variation of the third axial signal within a time interval exceeds a preset signal value, the detecting-calibration unit zeros the second axial signal within the time interval.

6. A moving trajectory generation method, comprising the steps of:

sensing a moving trajectory while a writing device moves on a written plane by a moving trajectory sensing module of the writing device, and generating a moving trajectory signal;

calibrating the first axial signal and the second axial signal according to the third axial signal by the detecting-calibration unit, so as to generate a first axial trajectory signal and a second axial trajectory signal; and

displaying the calibrated moving trajectory by a display module according to the first axial trajectory signal and the second axial trajectory signal.

7. The generation method of claim 6, wherein the moving trajectory signal comprises an angular velocity signal, an acceleration signal, a magnetic-field intensity signal, a geomagnetic orientation signal, or their combinations in three axes with respect to a moving trajectory at different time points.

8. The generation method of claim 7, further comprising the step of:

generating a coordinate transformation matrix according to the angular velocity signal by an orientation transformation unit of the orientation calculation module, and performing a coordinate transformation to the acceleration signals according to the coordinate transformation matrix.

9. The generation method of claim 8, wherein the orientation transformation unit integrates the angular velocity signal to obtain an orientation angle so as to generate the coordinate transformation matrix, and transforms the acceleration signals with the coordinate transformation matrix so as to transform the acceleration signals from a body frame of the writing device to a local level frame.

10. The generation method of claim 9, further comprising the step of:

performing a gravity compensation to the acceleration signal in the local level frame by a gravity compensation unit of the orientation calculation module.

11. The generation method of claim 6, wherein the step of calibrating the first axial signal further comprises:

12. The generation method of claim 6, wherein the step of calibrating the second axial signal further comprises:

13. The generation method of claim 6, further comprising the step of:

performing a calculation to the first axial trajectory signal and the second axial trajectory signal by a trajectory calculation unit of the orientation calculation module.

14. The generation method of claim 6, wherein the written plane comprises a horizontal plane, a vertical plane, or a slant plane.