4.2. Where are the Meta data?

The range of Meta data in the different layers of the ObservationContext (the Levels and the various contexts within the Levels) is not always the same, but there will always be a lot of commonality. Meta data are attached to the sliced products that make up the PACS Levels (e.g. SlicedFrames, slicedRebinnedCube—to the context and to the product (the frames and cubes) therein. Finally, any particular product—e.g. an image or a cube—will have meta data at the top-level and also meta data for the datasets (image, error, ...). To see the Meta data of any particular product, open the observation with the Observation Viewer (Chapter 2), the Meta data panel is located at the top:

Meta data in the Observation viewer

Figure 4.1. Meta data in the Observation viewer

You can also type Meta data out on the console, for example to see some of the Meta data added by the pipeline,

# On the individual slices (i.e. Frames)
print myframe.meta["nodPosition"]
print myframe.meta["lineId"]
print myframe.meta["rasterId"]
print myframe.meta["lineDescription"]
print myframe.meta["band"]
# Or also
print myframe.meta["band"].string
# Or, on slice 1 of the entire SlicedFrames (or Cubes)
print slicedFrames.getScience(0).meta["lineId"]

The Meta data are carried though to FITS files as keywords when a product is saved to disk: those associated with the entire product are in extension 0 (which in fact contains only keywords) and all the datasets in the product also have their keywords.