Region of Interest Object

[wafels]

It would be good to have a region of interest (ROI) object.

A ROI object would contain at least the following:

• bounds in the x, y, (potentially z) and t dimensions. For example, for a simple rectangle it would have x0, y0, x1, y1, t_start and t_end. For free-form shapes, you have to draw the path using chain-code (c.f. HEK).
• other flags indicating who/what generated the ROI and how.

Example use case:

User uses HEK module to get a list of events for some time range.
BBox info/chain-code from HEK results are automatically converted to SunPy RegionOfInterest instances.
Those instances can then be drawn as overlays on a Map instance, using something like "aiamap.show(overlays=hek_events)"

Here are some possible ways I could imagine creating a new RegionOfInterest:

 roi = RegionOfInterest(0, 0, 100, 100)                # x1, y1, x2, y2
 roi = RegionOfInterest(0, 0, 0, 100, 100, 100)   # x1, y1, z1, x2, y2, z2
 roi = RegionOfInterest([(79.500,-552.300),(80.100,-551.700),(94.500,-531.900), ...])  # chaincode (2d)
 roi = RegionOfInterest([(79.500,-552.300, 100.),(80.100,-551.700, 200.),(94.500,-531.900, 300.), ...])  # chaincode (3d)

# Shapes?
roi = RegionOfInterest(rect=[...])
roi = RegionOfInterest(circle=[...])
roi = RegionOfInterest(sphere=[...])
roi = RegionOfInterest(polygon=[...])

# Time support?
roi = RegionOfInterest(rect=[...], datetime = ...)
roi = RegionOfInterest(circle=[...], datetime = ...)
roi = RegionOfInterest(sphere=[...], datetime = ...)
roi = RegionOfInterest(polygon=[...], datetime = ...)
roi = RegionOfInterest(chaincode=[...], datetime = ...)

# Support for lots of them on plotting for Map
rois = [roi1, roi2, roi3,..., ]

aia.show(overlay = rois, useOverlayDateTime = True )
# only display ROIs that overlap with the map object datetime
useOverlayDateTime = True 
# ignore the ROIs map object datetimes and plot them all on the map
useOverlayDateTime = False 

See an older GSoC project: https://openastronomy.org/gsoc/gsoc2018/#/projects?project=region_of_interest

Extra

More generally it would be good to have an HEK event class that holds event
information. That could be an ROI or EOI factory, that understand HEK or other type of outputs.

WIP about extra methods

Could contain a number of functions (methods), such as 'GROW' or 'SHRINK' or 'ROTATE'.
There are many different ways to perform a "grow" and a "shrink" operation; scipy has a set of these operators under the "morphology" module

http://docs.scipy.org/doc/scipy/reference/ndimage.html#module-scipy.ndimage.morphology

I suppose you could pick one method and say "This is the default method", but you are not guaranteed to end up with something like you thought you were going to get.
For example, the "shrink" operation may end up splitting one ROI in to two unconnected ROIs.

How will we handle that? Is this what the user wants? On saying that, there are probably ways to ensure that you only ever return a single region after a "shrink" operation, but such considerations veer quickly in to the domain of image manipulation and away from a simple ROI object. I'm not saying it shouldn't be done, I'm just saying it requires some experimentation first.

[nabobalis]

Astropy have one now: https://astropy-regions.readthedocs.io/en/stable/index.html

We should investigate if this will work for us