Every mission required change to the schedule. For example, an unexpected experiment result excited a researcher on the ground to request that some new non-scheduled activity take place. The mission planners on the ground were trained to quickly make these changes using the Graphics Timeline Editor (GTE).
GTE provided the editing tools necessary for mission planners to quickly make conflict-free edits to the schedule. This was done by graphically displaying information about what the crew was doing and the usage of resources which are required for the activities being changed.
Example moving an activity forward on schedule
Usage
The Graphics Timeline Editor (GTE) was used to supplement the automatic scheduler when the user wanted activities placed on the timeline in a manner that the automatic scheduler could not do. In general, the automatic scheduler doesn't perform when -
- The requirements on a model are incomplete
- The requirements on a model are to be ignored
- The requirements cannot be modeled in the program's modeling schema
GTE contained algorithms that provided all that the normal editing features in addition to conflict-resolution assistance using a popular click and drag X-Windows interface.
Clipboard Concept
GTE was based on a "Clipboard concept". In this concept, what was in the clipboard was not in the timeline. Timeline events were moved to the clipboard, edited and committed back to the timeline. This concept reduced the permutations of potential conflict and allows for capabilities that would otherwise be too cumbersome or even impossible. Activities to be edited were moved to the clipboard, edited within the clipboard, and committed back to the timeline. When desired, a subset of the edited activities in the clipboard could be committed to the timeline. Activities from external sources could be added to the clipboard where possible conflicts could be resolved before they were moved to the timeline.
A picture of a typical GTE display is available in GIF (27 kb) format. The picture may seem large because it is; we use GTE on 21" screens with 1280x1024 resolution.
The tasks of GTE were accomplished by a combination of rendering the timeline as graphics objects and providing user manipulation of those objects.
Granularity Problem
When rendering the data, pixel granularity inherent in graphic editors was overcome by using a high resolution screens. However, when manipulating data, the pixel granularity problem is exacerbated in the clipboard because ESP could have a scheduling horizons of 90 days or more and simultaneously maintain time accuracies to 1 second; a ratio of 1 to 10 million. In addition, users of ESP frequently needed to maintain scheduling granularity at 1 minute. An eloquent solution to both problems has been implemented.
The clipboard provided two methods for addressing time granularity problems. First, time quantization was used to round modified times to the nearest multiple of a user-specified constant. During an activity modification, feedback provided the quantized placement times so the user is constantly aware of the modified value. Second, a mechanism which allows the user to make micro-adjustments was provided. Micro-adjustments are always made in a quantization unit even when the unit is smaller than a pixel.
Rendering Problem
When displaying the timeline, GTE was required to differentiate between crew-attended steps, unattended step, crew-monitoring sub-steps, and resource carry-through sub-steps. It was required to show overbooking of crew (both selected and non-selected). And, it was required to differentiate between selected (by the user for manipulation) and non-selected step and sub-steps. With permutations, twelve different rendering of a box were required. The rendering problem was exacerbated by three factors: 1- the requirement that GTE must be usable at a grayscale monitor (or by a color-blind user), 2- the requirement to show other information next to the bars, and 3- the scale/granularity problem. A multi-part solution is implemented -
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The four types of steps and sub-steps and sub-steps
were
drawn with different heights either centered or raised relative to the line
assigned to the performance.
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Selected activities are rendered with angled appendages. This method
provides optimum view-ability for overlapping and/or extremely small steps.
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Overbooking is rendered by filling the bar and drawing a line above it.
When the bar is only one pixel long, the "filling" doesn't material, but the
over-bar does.
Color was added as an enhancement.
Conflict Resolution/Prevention
The biggest drawback with many manual editors is their guess-again approach. When the user moves an activity, the scheduler response is to report resource constraint and scheduling conflicts and the user is forced to "guess again" where the activity can be validly placed to avoid the conflicts. In ESP, the clipboard not only provided a report when edits were committed, it also displayed graphics information to help the user eliminate existing conflicts and to avoid introducing conflicts when activities were manipulated.
Visual Aid for Crew Conflicts
Since ESP enforced the Spacelab and Space Station ground rule that a crewmember could not be scheduled to do more than one task at a time, the clipboard provided a crew timeline area, the crew clipboard data was overlayed, and any conflicts were highlighted. Users could readily see where crewmembers were available or were in conflict and could modify crew usage for activities in the clipboard.
Visual Aid for Resource Constraints
Each step of an activity could have many constraints which limit where on the timeline a step could validly be placed. In addition to crew requirements, the constraints included other shared resources and windows of opportunity. For each step, the clipboard could compare each requirement to the current timeline state, consolidate all the individual results, and present feasibility windows on a single line of the display. Windows which were not as long as the minimum step duration were not shown. By adhering to the feasibility windows, the user could easily avoid introducing conflicts or remove existing conflicts. A work procedure was also used for these feasibility windows. Figure 4 shows a step which was too long for its nearest feasibility window but which would fit within the next window.
Figure 4. Feasibility Windows.
Users could request that feasibilities for a step be presented on an individual requirements basis. This separate display would show each requirement of the selected step and the time periods when that requirement is met. The composite feasibility windows were also shown.
Other Major Features
Getting Activities into the Clipboard
Activities could be added to the clipboard by moving them from the current timeline to the clipboard, copying from the current timeline, importing from an external timeline, including a template of a model, using the automatic scheduler, and keying in data. Moving from the timeline to the clipboard was done by selecting the activity in the inspector and then choosing "move" from one of GTE toolbox dialogs.
Moving Activities
Moving activities was the most used manipulation of a timeline and therefore should be robust and easy to use. In the clipboard, moving selected steps was initiated with a mouse button press while the pointer is within one of the selected steps. The initiating step's new start time is fed back to the user during the modification to indicate where the step will be placed. Other selected steps are also moved.
Modifying Activities
After moving or adding activities, small conflicts would usually arise that require simple modifications for them to validly schedule as a group. For example, activity duration changes would routinely introduce overlap conflicts. By proper definition of activity duration changes, the user could prevent overlap conflicts. The definition chosen for the clipboard took all succeeding (for modified start time) or all preceding (for modified end time) activities which are selected and shifts them to maintain the original time delay between the changed activity and any other affected activity. In Figure 2 below, the duration of B was changed causing C to be shifted.
![[figure]](Pictures/gte_figure2.gif)
Figure 2. Duration Change.
However, when changing the duration of an activity, the durations of overlapping selected steps were also modified rather than being shifted. This overlap may or may not be due to scheduling concurrency constraints (see Figure 3 below).
Figure 3. Overlapping Change.
Modifying Crew Usage
A portion of the display could be used to display crew usage data for both the timeline and clipboard. Graphical manipulations within this area can remove, add, or reassign crew on an activity.
Undoing Modifications
Undo, as the name implies, allowed the user to undo the last edit made to the clipboard. The last edit may be either a simple (one item) or compound (multiple items) edit. In addition, undo can also restore activities to their unedited state until they are committed to the timeline.
Assisted Temporal Aligning
The clipboard can align selected activity steps or activity performances in four ways:
Steps are aligned consecutively in the order in which they were selected.
Committing to the Timeline
As stated before, activities in the clipboard were not in the timeline and must be committed to the schedule. During committal to the time line, activities were validated and any conflicts that the user has not resolved were reported. If no conflicts are present, the activities were moved from the clipboard to the timeline with no report.
Tailorable Displays
Each Spacelab mission ESP supports had different objectives and resource utilization. To accommodate the varying demands on the clipboard, a tailorable display allows users to home in on the information which is important to the type of missions they are scheduling. Some of the options included are -
Toolboxes
The Graphics Timeline Editor provided two toolboxes for quick access to frequently used features. The clipboard toolbox contains those features which primarily acted on the contents or the clipboard, and the timeline toolbox contain features which primarily acted directly on the timeline.
Clipboard toolbox.
Timeline toolbox.
The clipboard toolbox was on the same monitor as the clipboard, and the timeline toolbox is on the other monitor with the timeline inspector.