Purpose: specify panel rank reduction and implementation details.

Audience: Autoplot developers

See also: https://sourceforge.net/tracker/index.php?func=detail&aid=2809825&group_id=199733&atid=970682

Currently Autoplot's DataSourceFilter objects will reduce a rank 3 dataset to rank 2 for plotting. This was introduced to provide access to rank 3 data early in Autoplot's development. This has a number of shortcomings:

• multiple slices of the same dataset cannot be displayed without loading the data for each slice.
• only slices can be displayed, not collapsed (averaging over a dimension) data.
• rank 2 data cannot be sliced using this mechanism to provide a rank 1 view.
• rank 4 data cannot be sliced twice to provide a rank 2 view.
• future renderings of data may support viewing rank 3 data.
• this is not extensible, for example allowing new slice types.

allow dataSourceFilters to filter another dataSource. This leverages existing mechanisms, for example where the URI is vap+internal:data_1,data_2. This means that panels would need the authority to add dataSourceFilter nodes to reduce the data to an acceptable rank.

 data_1|slice0(23)
 data_1|slice0(23)|slice0(2)
 data_1|trim1(23,40)|histogram
 data_1|slice(energy=23)|slice(angle=2)
 data_1|collapse(where energy>1000)
 data_1(where data_2>0)    sql-like queries

extend the panel node's component property, which is just special a slice of the data, to include a full API.

 Bx     display a component to support legacy behavior
 |slice0(23)   pipe indicates non-component
 |collapse()   reduce the last dimension by averaging all leaf elements.

Rank 4 data is loaded from a CDF and the user wants to view rank 2 slices of the data. Autoplot resolves the rank 4 dataset and guesses the two dimensions for slicing. It provides a GUI to allow control of the two slices, and instead of slicing the user can trim and collapse a dimension instead. Title is updated to indicate slice location.

Support Bob's data filters, such as smoothing the data before viewing. Allow for view of histogram of the dataset.

Support view of dataset when other conditions are true. data_1(where(data_2.gt(0.) and data_3.gt(1000.)))

Slicing spectrogram panel configures the slice in the lower panel. This might mean that the lower panel's rank reduction spec (component property) would be bound to the upper panel's slice position.

Extending panel component behavior is the lowest impact way to introduce the functionality. The code that decides to break up a spectrogram into components is similar to what would be needed when a high-rank data set is encountered and must be sliced for display. It's possible that both should be introduced, so that operations can be performed in both the model and view of the data.

Performance is an issue, because we want to support slicing data on an animation-interactive time scale. This probably excludes the possibility of using Jython to implement. A parser that doesn't limit speed will be developed.

Clearly these specs are like URIs in that they are complex enough that humans won't be constructing them. Instead GUIs are provided to construct them.

dataSourceFilter.sliceIndex equal to -1 indicates that there should be no slicing. Legacy vaps should still work, except for the case where sliceDimension=0 and sliceIndex=0. This should not be difficult to deal with, because of the small number of vaps in the wild, and known instances were not slicing on the first dimension.