10.1 VIEWING PROCESS Once an analysis sequence has been digitized, transformed and smoothed, the Viewing module allows the three-dimensional image to be viewed in a stick figure format. Stick figures are created by connecting the body joint locations or external segments, like a golf club or tennis racket, with line segments according to the body connection information supplied when the sequence was created in the Digitizing module.
The stick figures may be displayed in single frame, multiple frames or animation mode with up to four different image sequences being viewed at the same time. The size, location and orientation of the stick figures for each sequence can be set in any manner desired to create comparison displays. Text labels can be added to the display to create complete illustrations and copies of the color graphic display may be printed from the color printer.
The viewing module is used in conjunction with the graphing and printing modules to obtain a complete presentation of image motion data for biomechanical analysis.
10.2 VIEWING OPERATION Select the Viewing Module from theMain Menu APAS. The first screen will ask for the number of windows to be used for viewing. From one to four windows may be selected. By providing multiple windows, the Viewing module allows comparison of different image sequences. Either images from different sequences may be viewed or different positions of the same sequence.
Each viewing window is independent of the others. Changing the content, size, or location of one window will not affect the contents of any other window.
The purpose of specifying the maximum number of windows to be used by the viewing module is to allow the graphic display memory to be partitioned in the most efficient manner. Each window is allocated a portion of the total display memory; the more windows, the smaller the portion of memory. The amount of memory allocated for an individual window determines the number of simultaneous stick figures that may be displayed in that window. For example, if only a single window is requested, all the display memory is used for that window and approximately 1000 stick figures can be simultaneously displayed. If two windows are requested, half the display memory is used for each window and approximately 500 stick figures can be displayed for each window.
When choosing the number of windows for viewing the lowest number that will suffice for the analysis is recommended. If only two sequences are to be compared, only two windows are needed.
After the number of windows have been chosen, the screen will list the sequences available in the current directory. As each sequence is chosen, the information relating to the sequence will appear in the Window Information Table located at the top of the screen. The table displays the name of the sequence, the current frame and frame time, and a number of status indicators for that window.
After each window has been chosen the Main Viewing Menu is displayed. On the color screen will be each window with the stick figure representation in it. Forward, Reverse, and Multiple are used to control the animation of the windows. Forward mode will run the stick figures forward and stop at the last frame. Reverse provides the opposite effect.
10.3 MULTIPLE/SINGLE In the multiple frame mode, the previous stick figure is not erased as each new stick figure is drawn. Animation in multiple frame mode produces an increasing number of stick figures in a manner similarly to a multiple exposure photograph.
This type of display is often used to view an entire activity and to observe the relative motion of the various body segments as the activity progresses. The Multiple/Single frame mode acts as a toggle switch, so when the multiple mode is selected, the Multiple item in the Main Viewing Menu changes to Single. At the same time, the indicator in the Window Information Table changes from Single to Multi.
10-4 WINDOW The Window Options Menu displays options that may be performed for each individual window.
10.4.1 Open/Close Open allows the user to open another window as long as the maximum number of windows are not being used. If the maximum number of windows are currently active, an error message will appear. As additional windows are opened, existing windows are moved to occupy quarters of the screen. In this manner, one window will not cover another.
Close is selected to remove any of the currently open windows. When close is selected a menu of active window numbers is displayed. Selecting the number corresponding to the window and pressing ENTER will close and remove both the graphic display and the information in the Window Information Table
When the Move option is select, a map of the graphic display will appear. The map shows the nine available window locations as a three by three grid.
10.4.3 Parameters Forward, Reverse, Multiple and Single can be used to create many type of still or animated displays. Additional animation options provide even greater viewing flexibility. These options are shown in the Window Information Table; INC, #FRAME, DELAY, ACTIVE and TRANS, and are accessed through the Parameters Menu. 10.4.3.1 Increment Increment is the frame increment value and is shown as INC in the Window Information Table. Each time the display is advanced to the next frame, either forward or reverse, the actual frame counter changes. The default value is initially set to 1 if there is enough display memory available for the window to contain all the stick figures in the sequence. If less display memory is available this item will be set to the lowest value that will allow the full sequence to be shown. The INC value may be changed at any time. An incremental value of 1 causes every frame in the sequence to be displayed during animation. A value of 2 causes every other frame to be displayed.
For example, a sequence may contain a large number of frames at short time intervals. When this sequence is displayed in the multiple frame mode, it may be difficult to distinguish the individual stick figures. By changing INC to a larger value, fewer stick figures will be shown thus making individual figures easier to discern.
10.4.3.2 Frames The number in the #FRAME column determines the total number of images that will be drawn for each sequence. The initial value is All which indicates that animation will continue until all the frames in this sequence have been displayed. If # FRAME is set to 1, then each time a forward operation is performed one new image will be drawn, thus animation is essentially turned off. This is frequently used when a frame by frame examination of motion is desired. When another value is used, only a portion of the image sequence occurs.
10.4.3.3 Delay The final animation option of the Window Information Table is DELAY. This number represents the delay time, in tenths of seconds, between consecutive images. The initial DELAY value is 0, which results in the fastest animation. To slow the animation rate, the DELAY value is set to a higher number. An abnormally high DELAY value will result in very slow animation. If the sequence contains a large number of frames, it may take a long time before animation is complete and control is returned to the keyboard.
10.4.3.4 Active The ACTIVE column acts as a toggle switch, allowing a window to be turned on or off. If a NO appears in the ACTIVE column then the window will not be animated whenever forward or reverse commands are issued, likewise if a YES appears then the window is animated. In this manner, it is possible to select animation for some windows and not for others.
10.4.3.5 Transform The TRANS column is another toggle switch, allowing each window to be either turned on or off for any transformation operations (Section 10.5) if multiple windows are open.
10.5 TRANSFORMATION OPTIONS Transformation is the term used for all operations that change the size, location, or orientation of stick figure images within a window. When a window is opened, the image is oriented so that the X axis is directed from the left to right, the Y axis is bottom to top, and the Z axis is direct out from the screen. Image axis are those of the control points discussed in Filming and Digitizing Chapters. The image size and location are selected so that the complete activity fills the window area selected from the sequence.
Although the default image display is often adequate for viewing and analysis, the viewing module allows the image size, location and orientation, of any of the active windows, to be changed in any manner desired. Selecting Transform from the Viewing Main Menu will display the Transformation Options Menu.
10.5.1 Orient The Orient option allows the image to be viewed along any one of the six standard axis directions. The default orientation, as mentioned above, presents the image viewed along the Z axis and is called the Front orientation. The other axis orientations and names are as follows:
The Orient option is performed on the currently selected window which is shown by the window indicator in the upper right corner of the Orientation Menu. If the indicator reads All, then all the active windows will be oriented.
The indicator may be changed by selecting the Window# option from the orientation menu and then selecting the window to be oriented.
10.5.2 Scale The scale option is used to change the size of an image in a given window. Images are frequently enlarged during analysis to show more detail for certain areas of activity. Scaling may be performed by one of following two methods.
10.5.5 Align This option allows an image to be oriented along the direction of a line connecting two data points (joints). These may be any two points in a single frame, the direction of a segment in that one frame, or they may be any single point in two different frames, the direction of motion of a point.
In this manner, images may be oriented in a direction that is significant for data analysis. For example, this option could be used to orient an image along the direction of flight of a baseball.
10.5.6 File The File option is used to change the default orientation of the sequence. When a window is opened the sequence is displayed with the image oriented in the coordinate directions of the control points that were used to calibrate this image. Sometimes the orientation of the control points is such that the image is displayed from an undesirable view. The Orient, Rotate and Align commands can be used to change the image orientation, but this is only a temporary change. Each time the window is closed and reopened with the same sequence, the original image returns.
The file option allows any changes to the orientation of the sequence to be saved as the default image. Because this option destroys the original orientation, and if the original is still desired, then a duplicate file should be made and changes made to the duplicate. This combination allows sequences to be oriented along significant data value directions for viewing, graphing and printing. Also, the File option only changes the image orientation, any change made to the size or location, done with Scaling and Translation, are not retained.
10.6 OPTIONS The Options Menu allows manipulation to the image inside the window. At times labels may be needed, vectors plotted, colors changed, or segments traced. The Options Menu provides these selections.
10.6.1 Labels The Label option is used to add text labels to any of the graphic displays. This provides a method for annotating images prior to making copies of the display. Labels can be in any one of four sizes, in a number of different colors and may be positioned in any location on the screen. Each time the label option is used, a new label may be added to the current display or all labels may be erased. Individual labels cannot be erased once they have been fixed to the screen.
Labels do not move once fixed to the screen and will not follow a particular window if the window is Transformed or Scaled. These operations should be performed before affixing labels to the screen.
10.6.2 Vectors The Vectors Option draws velocity and/or acceleration vectors for any point (joint) in the current frame of the window. A vector is a line whose direction is the direction of the corresponding joint velocity or acceleration and whose length is proportional to the magnitude of that quantity. Vectors are true three- dimensional objects and will be transformed with the original image when any transformation operation is performed. Velocity and acceleration vectors are used in analysis to show the direction and magnitude of motion at any particular instant in an image sequence. Vectors remain on the display until the Erase option is selected at which time all vectors are cleared. Thus, if vectors are drawn for the current frame and then the image is animated forward or reverse a number of frames, the vectors will no longer correspond to the image being viewed. The first vector drawn after each Erase is always a fixed length. Subsequent vectors are drawn to the scale of the first vectors, so that the length of each vector is proportional to the velocity or acceleration quantity it represents. If the first vector represents a quantity that is very small compared to subsequent vector quantities, some of the vectors may extend beyond the edge of the window and be clipped.
10.6.3 Colors The colors option is used to change the colors of various objects on the graphic display. When colors are changed, the changes are saved and used each time the viewing module is run. Colors may be changed for each of the four viewing windows, for the display background, and for the logo. Colors are selected from a menu of sixteen possible display colors. If an item is changed to the background color it will disappear.
10.6.4 Trace The trace option allows the user to install up to two trace lines on an image. Any of the points (joint) of the image including the center of gravity may be selected. Trace point information (Figure 10-8) is selected by scrolling through each of the fields and then pressing the ENTER key. If the ENTER key is not pressed then the information will not be changed.