Linking Requirements

These requirements link all passes within the selected Survey Steps and specify constraints that apply to each pass within the step.

To add a linking requirement, click Linking Requirements on the Survey Plan form, click Add, then select a requirement. 





After

Schedule SURVEY STEP after SURVEY STEP by MIN INTERVAL to MAX INTERVAL

This requirement links two Survey Steps and specifies that one step must start within a specified time interval after the start of the other step. All passes in the selected steps are linked with the specified time interval.

Survey Step

The step to be observed after the first. Select a step from the list of all Survey Steps in the program. 

After Survey Step

The step to be observed first. Select a step from the list of Survey Steps in the program.

Minimum/Maximum interval between steps

  • Enter a minimum and a maximum interval. Allowed range is 0 to 10000 days .
  • Select units.  Options are Days or Hours.
  • Max Interval must be greater than Min Interval by at least 4.0 Days.

Link chains are not allowed (example: "3 After 2" combined with "2 After 1"). Link chains can be restructured so that all of the links in the set refer to the same starting
point, for example "3 After 1" and "2 After 1". Alternatively , the Time Series requirement can be used to link passes within multiple steps. 

Overlap is allowed (example: 2 after 1 by 30-40, 3 after 1 by 35-45).

Time Series 

Time Series SURVEY STEP ... SURVEY STEP at period of PERIOD +/- TOLERANCE

This requirement specifies the period between each Pass in one or more selected Survey Steps, within a specified tolerance. Linked passes must start within the period after the start of the previous pass.

The APT Time Series dialog box displays the total number of linked passes in the selected steps. For example: "5 Passes spaced over approximately 1460 Days"


Figure. Scheduling with a Time Series Requirement










In this example, the Time Series requirement is  "Time Series 1, 2, 3, 4, 5 at period of 365 Days +/- 30 Days" (shown in the Time Series dialog box). The Visit Planner shows schedulable days with this requirement.


Survey Step

Select one or more steps from the list of all Survey Steps in the program. The selected steps must have a combined total of two or more passes.

Period

Enter the period between passes. For example, a period of 5 days means the next pass must start 5 days from the start of the previous pass. Units are Days or Hours.  Allowed range is 4.0 days to 365.0 days .

Tolerance

Enter the tolerance for deviation from the period. For example, a tolerance of 1 day means the each pass may start +/- 1 day of the exact period. Units are Days or Hours. Allowed range is >= 1 day and must be no more than one-half the period.

The overall time series cannot stretch or compress:

  • For example, if the period is 5 days, then the nth pass starts 5*n days from the start of the first pass. 
  • If a pass comes early in the tolerance window, subsequent passes are not moved earlier.

Same V3 PA

same V3 PA SURVEY STEP ... SURVEY STEP

This requirement specifies that all passes within the selected Survey Steps must be observed at the same orient (V3 position angle). 

V3 PA Offset

V3 PA offset SURVEY STEP from SURVEY STEP by  MAX PA OFFSET to MIN PA OFFSET degrees

This requirement links two Survey Steps and specifies that one step must be observed at a V3 Position Angle offset from V3 Position Angle of the other step by a specified range (in degrees).

Orient Survey Step

The step that is to be observed at an offset. Select a step from the list of all Survey Steps in the program. 

Offset From

The step to offset from. Select a step from the list of all Survey Steps in the program. 

Min/Max PA Offset

Enter the minimum and maximum offset in degrees. Range is  -180 to 180 degrees .

If necessary, it is possible for MIN PA OFFSET  and MAX PA OFFSET  to be equal, which greatly restricts the time the observation can be scheduled. For this reason, the difference between the two limits should be as large as possible to make scheduling easier.

Both angles are measured in a counterclockwise direction:

  • If the position angle region crosses a point 180 degrees from the first SURVEY STEP , MIN PA OFFSET  should be positive and MAX PA OFFSET  negative.
  • Otherwise, MIN PA OFFSET  should be less than MAX PA OFFSET . It is possible for the position angle region to be larger than 180 degrees.



For additional questions not answered in this article, please contact the Roman Help Desk at STScI.



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