Visualized Instruction for Posture Rectification

Our proposed YogaST system is capable of assisting the practitioner in practicing twelve asanas, including (1) Tree, (2) Warrior III, (3) Downward-Facing Dog, (4) Extended Hand-to-Big-Toe, (5) Chair, (6) Full Boat, (7) Warrior II, (8) Warrior I, (9) Cobra, (10) Plank, (11) Side Plank, and (12) Lord of the Dance, as given in Table 1. Since each asana has its own postural emphasis (please refer to [34]), different dominant axes and representative points are

28

used to describe the postures of different asanas and provide visualized instruction for posture rectification. In the following, we will elaborate each asana in detail

(1) Tree is a basic pose in Yoga, as shown in Fig. 3-14, which emphasizes that the body should be upright and maintains balance. As shown in Fig. 3-14(c) and (d), Phigh and Plow are the highest and lowest points in contour-based representative points, and O1 is the centroid of the user body. Then, we connect O₁ to P_high and P_low, termed axes L₁ and L₂, respectively.

Thus the axes L1 and L2 can reveal whether the practitioner is tilting in the front or side view, as well as display the tilt angles.

Fig. 3-14. Original frames and visualized instruction for Tree pose.

(2) Warrior III, as shown in Fig. 3-15, is kind of a difficult pose that the arms, torso, and raised leg should be positioned relatively parallel to the floor, with balance maintained by the other leg. As shown in Fig 3-15(c), L₁ and L₂ are extracted in the same way as Tree pose

29

and used in front view to reveal if the practitioner is tilting. In the side view, we extract the point O2 by locating the intersection of Vx and Hx, as shown in Fig. 3-16. Other points are obtained from the contour-based representative points: P_left for the leftmost point, P_right for the rightmost point, and Plow for the lowest point. Then, we connect O2 to Pleft, Pright and Plow for deriving L3, L4, and L5. As show in Fig. 3-15(d), L3 and L4 are used in the side view to measure whether the arms, torso, and raised leg are parallel to the floor. The angle between L₃ and a horizontal line suggests that the arms and torso can be a little lower, while the angle ө between L₄ and a horizontal line is displayed, reminding the practitioner to raise the leg higher.

Fig. 3-15. Original frames and visualized instruction for Warrior III pose.

30

Fig. 3-16. Illustration of the point O2 extraction: Extract the point O2 by locating the intersection of Vx and Hx.

(3) Downward-Facing Dog is an essential pose in the majority of yoga classes that the hands are put on the floor, and the back should be lengthened along its entire length so that the arms and back form one line, as demonstrated in Fig. 3-17. Besides, legs should be stretched and straightened. In the both views we extract the leftmost, the rightmost and highest point from the contour-based representative points, named Pleft, Pright and Phigh. As shown in Fig. 3-17(c), we connect the centroid of the body map to Phigh, Pleft, and Pright, termed L1, L6, and L7, respectively. L1 in the front view can disclose the left or right tilt of the body. As shown in Fig. 3-17(d), we connect P_high to P_left and P_right, termed L₈ and L₉, so as to indicate whether the arms and back (colored red) form one line and whether the legs (colored green) are straightened.

31

Fig. 3-17. Original frames and visualized instruction for Downward-Facing Dog pose.

(4) Extended Hand-to-Big-Toe is a pose that helps in stretching the hamstrings so the practitioner performing this pose have to stand straight, slowly swing the foot to the front, and maintain the balance, as shown in Fig. 3-18. Here, the raised-leg foot is raised as higher as possible. As demonstrated in Fig. 3-18(c), we show the same visualized instruction as Tree pose. In the side view, we locate O2 in the same method as Warrior III pose by extracting the intersection of V_x and H_x and connect O₂ to the derived contour-based representative points Phigh, Plow, and Pleft. As show in Fig. 3-18(d), the axes L1 and L2 assist us to reveal whether the practitioner is tilting and L3 directs the degree of the raising leg.

32

Fig. 3-18. Original frames and visualized instruction for Extended Hand-to-Big-Toe pose.

(5) Chair, as shown in Fig. 3-19, is a pose that the practitioner sits back with raising his/her arm overhead. The practitioner should keep the natural curve of his/her lower back, finding balance between drawing in your lower belly while sending your tailbone towards the earth. Because the pose is just like sitting on a chair, the thighs should be relatively parallel to the floor. As shown in Fig. 3-19(c), L₁ and L₂ are extracted for analyzing the front view. On the other side, we attempt to obtain the key joints from the corner-based representative points.

As illustrated in Fig. 3-20, we sort these points according to their y-coordinates, termed as P1, P₂, … P_n, and we eliminate a point P_i if the angle of and is larger than a threshold. In general cases, we extract two points P₄ and P₅, also named P_joint1 and P_joint2 in Fig. 3-19(d). In addition, we locate the lowest point of the contour-based representative points, Plow and the highest point Phigh of the contour-based representative points. According to these

33

extracted points, we obtained L₁₁, L₁₂, and L₁₃, as illustrated in Fig.3-19(d). The axis L₁₃ is appropriate to reveal whether the thighs of practitioner are relatively parallel to the floor.

Fig. 3-19. Original frames and visualized instruction for Chair pose.

Fig. 3-20. Illustration of representative point extraction in chair pose. (a) Corner-based representative points. (b) Representative points extraction in chair pose.

34

(6) Full Boat is a great yoga pose for strengthening the abdominal organ. As presented in Fig. 3-21, the practitioner sits on the floor and lifts his/her feet off the floor. Then, the thighs are angled about 60 degrees relative to the floor. As show in Fig. 3-21(c), in the front view, the analysis is the same as Tree pose. In the side view, first we extract the leftmost and the rightmost point from the points of the corner map, termed Pjoint_left and Pjoint_right. Second, we obtain the center O₁ and the lowest point of contour-based points P_low. Third, we locate O₃ at (x-coordinate of O1, y-coordinate of Plow) and connect O3 with Pjoint_left and Pjoint_right, termed L₁₄ and L₁₅, as shown in Fig. 3.21(d). Finally, L₁₄ assists the practitioner to adjust his/her feet lower or higher.

Fig. 3-21. Original frames and visualized instruction for Full Boat pose.

(7) Warrior II is a beautiful pose that inspires grace and strength, as presented in Fig.

3-22. First, the practitioner steps his/her feet apart. Second, he/she raises his/her arms

35

(P_{right_low}) as the lower point. In order to confirm the calf is perpendicular to the floor and the thigh is parallel to the floor, we locate the Pjoint4 and Pjoint3. In order to extract the key joints of the leg of the practitioner, we take the point O₁ as the origin and separate the body map into four quadrants, termed LH, LL, RH, and RL, as shown in Fig. 3-23, and then we sort the points in LL in descending order and the points in RL in increasing order of their y-coordinates and we have the sequential points of the two legs. In the normal case we derive the Pjoint3 as the highest point of LL and the Pjoint4 as the second point of LL. In the upper part of the body, we locate the point that is nearest to the middle point of P_high and P_joint3, termed Pjoint5 and connect Pjoint5 with Pleft_high and Pright_high, termed L16 and L17. We connect Pjoint3 with Phigh, termed L18. In the lower part of the body, we connect the Pjoint4 with Pleft_low and Pjoint3, termed L₁₉ and L₂₀. As shown in Fig. 3-22(d), the axes L₁₆ and L₁₇ assist us to verify whether the arms of practitioner parallel to the floor, the axis L18 assist us to verify if the practitioner is tilting and the axes L₁₉ and L₂₀ assist us to reveal the angle of the thigh and the calf.

36

Fig. 3-22. Original frames and visualized instruction for Warrior II pose.

Fig. 3-23. Illustration of separating the corner-based representativepoints.

(8) Warrior I is a pose similar to Warrior II, as shown in Fig. 3-24. The lower part of the body is the same as Warrior I but the arms of the practitioner are raised to the side of shoulder height and parallel to the floor. In the front view, we extract Phigh_mid as the middle point of two highest contour-based representative points and connect O₁ to P_{high_mid} and P_low, termed L21 and L2, as show in Fig. 3-24(c). In the side view, we obtain L18, L19, and L20 in the same

37

method as the Warrior I pose. Then we display instruction according to these axes as shown in 3-24(d).

Fig. 3-24. Original frames and visualized instruction for Warrior I pose.

(9) Cobra is a great exercise for people with lower back aches, as shown in Fig. 3-25.

The practitioner lies face down on the floor with the palms flat, placed beneath the shoulders.

Then, the practitioner pushes his/her upper body off the floor and straightens the arms as much as is comfortable while keeping the hips, legs, and feet planted on the floor. Note that do not overdo the back bend, otherwise it may cause injury. In the front view, we apply the same method as Downward-Facing Dog pose, as shown in Fig. 3-25(c). In the side view, we aim to obtain the curve of the main part of body. In this asana we take the point O1 as the center and separate the user body map into 2 parts, termed LP and RP, as shown in Fig. 3-26.

Then we sort the corner-based representative points in LP in increasing order of their

38

y-coordinates and sort the ones in RP in increasing order of their x-coordinates. In order to reveal the curve clearly, we eliminate the points near the Pleft and the point Pi that the angle of and is larger than a threshold. As shown in Fig. 3-25(d), we keep P joint_high, Pjoint5, Pjoint6, and Pjoint_right, and connect them according to their position. Here, we obtain L21, L22, and L23, and use them to display whether the practitioner is overdoing the back bend.

Fig. 3-25. Original frames and visualized instruction for Cobra pose.

Fig. 3-26. Illustration of separating the corner-based representative points.

(10) Plank is an arm balancing yoga pose that tones the abdominal muscles while

39

strengthening the arms and spine. As shown in Fig. 3-27, the practitioner puts the hands on the floor and brings the body into one straight line, from shoulder to heels.In the front view, we apply the same method as Downward-Facing Dog pose, as shown in Fig. 3-24(c). In the other view, we extract the point which is highest point of the points that their x-coordinates are close to the x-coordinate of Pleft_low from the corner-based representative points, termed P_joint7. According to the adult body proportion [35], as shown in Fig. 3-28, the ratio of the distance from the shoulder to the hip to the distance from the hip to the feet is about 2:4. We define P_joint7 as the shoulder and P_right as the feet and then we obtain the P_joint8, of which the location is closest to the ideal location of the hip from the corner-based representative points.

As shown in Fig. 3-27(d), we connect Pjoint8 to Pjoint7 and Pright, termed L24 and L25, and use these two axes to infer if the body of the practitioner is presented in a straight line.

Fig. 3-27. Original frames and visualized instruction for Plank pose.

40

Fig. 3-28. Illustration of human body proportion [35].

(11) Side plank challenges the stability and improves core strength by working the muscles along the side of your body. As shown in Fig. 3-29, the practitioner starts the pose by lying on the side with legs straight and feet stacked. Then, the practitioner straightens the bottom arm, raises the hips until the boy forms a straight line from the shoulder to the ankles and extends the other hand toward the ceiling.In the front view, we apply the same method as Tree pose, as shown in Fig. 3-29(c). In the side view, first, we extract O₂ in the same way as Warrior III pose and obtain the point nearest to O2 in the corner-based representative points, termed P_joint9. Second, we define P_joint9 as the shoulder and apply the same method as Plank pose to attain the hip point, termed Pjoint8 in Fig. 3-29(d). Third, we connect the Pjoint8 to Pjoint9

and Pright, termed L28 and L25. In the part of the arms, we connect Pjoint9 to Phigh and Plow, termed L₂₆ and L₂₇. Finally, we use axes L₂₆ and L₂₇ to reveal if the practitioner's arms are put in a straight line and use L28 and L25 to infer if the body of the practitioner is presented in a straight line, as shown in Fig. 3-29(d).

41

Fig. 3-29. Original frames and visualized instruction for Side Plank pose.

(12) Lord of the dance requires the pose to be done gracefully, almost like a dance, as shown in Fig. 3-30. The first is to reach back with the left (right) hand and grasp the outside of your left (right) foot or ankle. Then, the practitioner begins to lift the left (right) foot up, away from the floor, and back, away from his/her torso with stretching the right (left) arm forward, in front of your torso. As shown in Fig. 3-30(c), we apply the same way as Tree pose in the front view. In the side view, the practitioner has to keep the balance and try hard to raise his back foot as higher as possible so we extract Pright_high as the back foot. Additional we locate the point P_joint10 which is closest to P_{joint_high} in the corner-based representative points and connect Pjoint10 to Pright_high, termed L28. As shown in Fig 3-30(d), L28 assist in revealing if the practitioner's back foot is raised enough.

42

Fig. 3-30. Original frames and visualized instruction for Lord of the Dance pose.

43