Movement in the Viewer Space
The user has a view into the imaginary three-dimensional space that contains the timelines. The view is composed by setting a viewpoint, a view direction, and the scale of the axes. The viewpoint is where the user's eye is located in the imaginary space, and the view direction is where the user is looking. Moving the viewpoint is broken down into movements along the three axes in the space: x, y and time. Although the user could look in any direction from the viewpoint, the view directions have been limited to the four most useful. These are towards the past and future along the time axis, and towards the left and right down the x axis.
In the standard mode the axes of the controller correspond to the axes in the imaginary space. These do not change when the user changes view direction. In first person mode the axes of the controller change to match the view direction. For example, movement in the x axis controller will always move left and right across the screen even in the left or right view when this produces movement in the time axis. This mode can be enabled in the user preference window.
The values of x and y are the location of the viewpoint in the two axes of the category plane. The x and y axes correspond the the left/right and up/down directions when the user is looking towards the past or future along the time axis. (Left and right are defined by the direction to the future when facing that direction.)
The time axis (by convention, the z axis) runs from the distant past to the distant future. Movement of the viewpoint along this axis changes the display time of the QViewer forward or backward in time. The display time is printed in the datetime box on the display.
The display time forms the front clipping plane of the display when the view direction is either towards the past or future. When looking towards the future, no events or parts of events before the display time are visible. When looking towards the past, no events or parts of events after the display time are visible.
When the view direction is towards the left or right, the display time is indicated by a thin gray line running from top to bottom at the center of the display area. This line represents the plane of the display time turned sideways.
Normally, the user directly controls movement of the QViewer's display time. There is a command that turns real time mode off and on. When this mode is on, the display time updates automatically, then redraws the display area. This allows the QViewer to be used as a clock, a calendar, a player for a set of songs, or a viewer for a set of images.
Real-time mode can be started from any display time and will count forward from that time. If the user intends for real-time mode to be synchronous with clock time, the set time to clock time command will set the display time to the current clock time. This command can be used while real time mode is running. but any other change to the display time by typing a new value in the datetime box, or by using one of the movement input devices, will turn off real-time mode.
A display with many complex events might take more than a second to redraw the display area. In this case, the datetime box may not show the new time at regular intervals.
The x/y scale is a number that is multiplied by the position and size values along the x and y axes to cause events to appear larger or smaller in those dimensions. This is important because the ability of the QViewer to nest categories inside other categories means that at a certain level of nesting the categories will be very small. Scaling the x and y axes allows the user to expand the events in categories at the center of the display area.
The x and y axes are always scaled together. This means that the width and height of events maintain the same proportion.
The time scale is a number that is multiplied by the time values along the time axis to make the durations they represent larger or smaller on the display. The ability to continuously scale the time axis means that the QViewer can show events lasting billions of years as well as the shortest events ever physically measured.
Changing the time scale affects the widths of the divisions of the time ruler. It also determines when the divisions change to represent different time increments.
Changing the time scale affects how much detail is printed with the date and time in the datetime box.
Changing the time scale can change the automatic level of detail in categories that have time scale mappings. Changing the level of detail may change which events are drawn on the display area.
The QViewer supports only four view directions: facing the future, facing the past, facing left and facing right. The current view direction is always indicated by the compass rose in the lower left corner of the viewer. The four arms of the compass are buttons that can be hit to change the direction.
The limitation to four directions is arbitrary. The four directions were chosen for simplicity and because they are the most useful for the purpose of visualizing time relationships.