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Below is the proposed new table structure for Images and Image Products in the metadata database. There are 4 classes of columns below: initial columns, new columns, columns adapted from (previous_column), and columns renamed to match their equivalents in the observation tables. Depending on the design decisions and the behavior of CASA, some of these fields could be removed (t_xel, em_xel, pol_xel) if they they will be invariant.
Images Database Table:
| Column Name | Units | VO Equivalent | Source | Comments |
|---|---|---|---|---|
| sourcename | target_name | OBJECT Keyword | ||
| ra (center_position) | deg | s_ra | Center of Ra Axis | |
| dec (center_position) | deg | s_dec | Center of Dec Axis | |
| field_of_view | deg | s_fov | Average of NAXISn*CRDELn of the spatial Axes | |
| spatial_region | s_region | Derived from spatial Data | STC-S String Defined in the TAP (Dowler, et al 2010) | |
| ra_element_count | s_xel1 | Relevent NAXISn Keyword | ||
| dec_element_count | s_xel2 | Relevent NAXISn Keyword | ||
| spatial_resolution | arcsec | s_resolution | Average of CRDELn of the spatial Axes, converted from deg | |
| starttime | MJD | t_max | Temporal domain information for an image is dependent upon the observation(s) used in its generation. Some controlling process (Like Vlass Manager, whatever imaging pipeline we create, and any image manipulation software we use) will need to supply it. | |
| endtime | MJD | t_min | ||
| exposure_time | s | t_exptime | ||
| min_frequency observing_band) | Hz | em_min | Minimum of Spectral Axis | The spectral information is recoverable from the FITS header, and will identify the spectral coverage, and total bandwidth processed for the image. (TBD: what further information for unit conversion for the VO? (Hz → m)) |
| max_frequency (observing_band) | Hz | em_max | Maximum of Spectral Axis | |
| spectral_resolution | unitless | em_res_power |
| Center Frequency/CDELTn | ||||
| polarization_code | pol_states | Currently, there is insufficient information provided about the polarization information of the image in the quicklook FITS headers. There is a STOKES axis, but no further information is provided. Since Single Epoch images will be created in Stokes I, Q, and U, that information must be provided to distinguish the files. Adding the stokes parameter name to the CTYPEn or CUNITn header keywords would solve this issue. | ||
| telescope | instrument_name | TELESCOP Keyword | This must accommodate images for multiple instruments (i.e. VLA + Single Dish) | |
| file_id | automatically generated | link to information about the physical file | ||
| image_id | obs_id | automatically generated | Unique Identifier for the Image | |
| image_units | o_ucd | BTYPE & BUNIT Keywords | Description of the physical quantity measured in the image | |
| max_intensity | image_units | These values are can be determined from the data portion of the image file in conjunction with the BSCALE & BZERO keywords. The library which is used for FITS interaction for ingestion can perform these calculations, but no information about the speed of results is yet available. | ||
| min_intensity | image_units | |||
| rms_noise | image_units | |||
| thumbnail | weblog, a PNG with identical name |
FITS Data Description Keywords:
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