spectral_analysis bigpicture

From a discussion in SSB:

[...] the more complex uses centered around two basic tools. One tool visualizes spectra and models for the spectra as well as accepting graphical user input about various things (some modifying the visualization, some modifying the parameters for fitting.

The other tools is coupled to the visualizer, but is something that could be coupled to a variety of things. It handles the display of information about model fits. In this interface, one presumably can change aspects of the models and fitting (with some overlap with values obtained from the spectrum visualization tool). It is in this tool one might add more spectral components to fit, designate which parameters are fixed and which are to be fit, and constraints on fits. This tool is not visual in the graphical sense, but choices here may affect visual elements in the visualizer.

I outline these two so that I can describe use cases for each with the understanding that some expected functionality for one actually may appear in the other.

1D spectrum visualizer Use Cases

1. display spectrum, pan, zoom, save plot (both hard copy, and info on how to regenerate plot in a script for a more elaborate plot from an enhanced script). Show world coordinates for both axes and cursor. Modify units of world coordinates.

2. create model elements for displayed spectrum (e.g., add continuum model, gaussian emission or absorption lines). Select fitting domains for each. Invoke fits for those models. Display fit results, and residuals of fits, for individual model components, or for the sum of all components. Save model info.

3. overplot multiple spectra in same plot window. (through an expression window?, allow expressions to create new spectra to be plotted, e.g., subtract one spectrum from another. Perhaps have a plot element list to allow highlighting selected elements on the plot, and allow selecting plot element by clicking on the element in the plot window.

Model tools Use Cases

1. Add or delete model components (addition overlaps with same capability in visualizer; presumably visualizer invokes it for the model tool). Mark model parameters as fixed or free. Add model constraints (individually, e.g., must be positive; or tie different model component parameters together, e.g., ratios of wavelengths must remain constant, or share same sigma). Invoke fits, adjust fit parameters (number of iterations, convergence criteria, fitting engine...) If models are currently plotted, change appropriate plots in spectrum visualization for any change in models.