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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)other columns , 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.
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| 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)dec | deg | s_dec | Center of Dec Axis | ||||
| image_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 | sqrt(BMAJ*BMIN) | Geometric mean of the synthesized beam axes. | |||
| beam_axis_ratio | BMAJ/BMIN | Ratio of the synthesized beam axes. | |||||
| starttime | MJD | t_min | 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. , and the details of the processing. Without an outside source of information, these values will be 'null' | ||||
| endtime | MJD | t_max | |||||
| exposure_time | s | t_exptime | |||||
| min_frequency observing_band) | Hz | em_min | Minimum of Spectral Axis | ||||
| max_frequency (observing_band) | Hz | em_max | Maximum of Spectral Axis | spectral_resolution | unitless | em_res_power | |
| rest_frequency | Hz | RESTFRQ Keyword | Used for transformations | ||||
| band_code | From frequency range | Include all receivers used for the image. | Center Frequency/CDELTn|||||
polarization_id (reverting to initial name) | pol_states | Polarization CRVALn value | CASA uses the CRVALn value to convey polarization information, with [1,2,3,4] mapped to [I,Q,U,V]. When we begin dealing with single-polarization images, this will need to be expanded. Default to 'None' in case of other values. | ||||
| 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 |
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| VO Requirement | Value | Source |
|---|---|---|
access_url | ||
| access_estsize | files.filesize, or combined value for an image set | |
| dataproduct_type | 'image' | default |
| access_format | 'fits' | default |
obs_publisher_did | Obtained upon registering with the Virtual Observatory | |
| facility_name | 'NRAO' | default |
| t_resolution | images.imageexposure_integration_time | |
| t_xel | 1 | default |
| em_res_power | null | default |
| em_xel | 1 | default |
| pol_xel | 1 | default |
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