Images

Ingesting FITS images allows for their retrieval via the a multi-band Image Cutout service. This service allows astronomers to easily and intuitively access imaging data from some of the world’s leading facilities alongside datasets of national significance, to quickly explore sources of interest and produce publication quality images.

The Image Cutout service allows for comparison of the same source at different wavelengths side by side. Users can input a single source/position or a list (automatically transforming between the submitted coordinate frame and the native coordinate frame of the image) to generate single bands and/or three-colour images.

Five image scaling options are supported, along with custom plot options (axes style, colour map, coordinate grid), over-plotting source positions from any of the DC-hosted input catalogues as well as remote VO datasets, and over-plotting contours for a particular band at user-specified levels. Users are able to download results as .png or .fits files, on a per-band/per-source basis, or download all the files from one request.

The cutout can host mosaiced image files in a range of projections and pixel scales, automatically reprojecting data on the fly.

Note

Remember that the documentation mentioned here is uneditable once the data are released. Documentation intended for public use and/or subject to change (e.g., with detailed descriptions of analysis or version update information) should be maintained by the survey teams in Data Central’s Documentation portal: Documentation Central.

Data Model

Data Central’s ingestion process will map your data onto the Data Central data model. Within Data Central, imaging data are organised hierarchically, as per:

<survey>
└── <datarelease>
    └── Schema:Imaging
        └── Facility
            └── Band
                └── Region

Currently, the Image Cutout service is not able to stitch together imaging on the fly. You must provide FITS images that have been resampled and co-added (see for example, SWarp.) Each file is saved as a Region on the sky, with the FITS header stored in the database to provide the coordinate lookup. Note, this means individual region files must uniquely cover one area of sky. Data central can not currently combine or display multiple images in the same band covering the sam sky region. To explore the data model further, visit the imaging section of the Schema Browser to explore the relationships between facilities and bands.

Directory Structure

To ingest imaging data into Data Central, you will provide two folders, one containing the data products files themselves, and one containing the metadata.

Data

The imaging directory should contain the FITS files themselves.

data
└── <survey>
    └── <datarelease>
        └── imaging
            ├── swpim_galex_FUV_d10.fits
            └── swpim_galex_NUV_g09.fits

Attention

<survey> and <datarelease> should be replaced with the values you chose in Getting Started, e.g., gama and dr2.

Data Central supports images in .fits format only. Note, these data files can have any file name, as long as they are correctly matched in your metadata files (see below). We strongly suggest using sensible file names that describe the facility, band, survey and region.

Metadata

The following file structure should be adopted. A top-level <survey> directory should contain a single directory per <datarelease>. Please follow the directory format indicated below. The metadata files will populate the Schema Browser.

dcmetadata
└── surveys
    |____ <survey>
    ├──── <survey>_survey_meta.txt
    └──── <datarelease>
          ├── <survey>_<datarelease>_data_release_meta.txt
          └── imaging/
              ├── <survey>_<datarelease>_facility_meta.txt
              ├── <survey>_<datarelease>_band_meta.txt
              └── docs/                                     ** optional

The dcmetadata/surveys/<survey>/<datarelease>/imaging/ directory will contain 2 metadata files, plus an optional docs/ directory if you have supplied additional documentation for a particular facility/band.

Metadata Files

Attention

Metadata files are always pipe-delimited, and have the extension .txt.

<survey>_<datarelease>_facility_meta.txt

This file describes the facilities you would like to register, and will be used to populate the Schema Browser.

Please provide a single pipe-delimited .txt file containing an entry (row) for each facility, in the following format:

name	pretty_name	description	documentation
CFHTCFHTCOSMOS	CFHT	Images from the CFHT COSMOS survey.	unique_cfht_documentation_filename.txt

Please name this file: <survey>_<datarelease>_facility_meta.txt, replacing <survey> and <datarelease> with the survey name and datarelease name, respectively: e.g., sami_dr2_facility_meta.txt.

<survey>_<datarelease>_facility_meta.txt

This file should contain the following columns:

name(required=True, type=string, max_limit=100)

Facility name. Use only alphanumeric characters. This must be unique per data release.

pretty_name(required=True, type=string, max_limit=500)

A human-readable version of the facility name. This can contain any characters (up to the character limit).

description(required=True, type=string, max_limit=500)

A succinct paragraph describing the facility.

documentation(required=False, type=string, max_limit=1000)

If you would like formatted text to appear in the Schema Browser, you must supply a file in the docs/ directory. The file can be either plain text or markdown-formatted text (see Formatting for more info). This field is set to the name of the file. If you do not wish to supply documentation for a particular group, leave this entry blank. Remember that the documentation mentioned here is uneditable once the data are released. Documentation intended for public use and/or subject to change (e.g., with detailed descriptions of analysis or version update information) should be maintained by the survey teams in Data Central’s Documentation portal: Documentation Central.

<survey>_<datarelease>_band_meta.txt

This file describes the bands you would like to register, and will be used to populate the Schema Browser and be available to select in the Image Cutout service.

Please provide a single .txt file with an entry per file (each file should have a corresponding unique ‘region’), containing the following meta information:

name	pretty_name	start_wave_ang	central_wave_ang	end_wave_ang	spatial_res	start_time	end_time	pol_state	facility	description	documentation	contact	version	file_name	region	is_displayed
H	H	14629	16499.11	18085	0.5				CFHTCFHTCOSMOS	COSMOS H-Band	unique_h-band_doc.txt	name <email@institute.org>	v02	swpim_cfht_H_d10.fits	d10	Y

Please name this file: <survey>_<datarelease>_band_meta.txt, replacing <survey> and <datarelease> with the survey name and datarelease name, respectively: e.g., sami_dr2_band_meta.txt.

<survey>_<datarelease>_band_meta.txt

This file should contain the following columns:

name(required=True, type=string, max_limit=100)

Band name. This must be unique per data release.

pretty_name(required=True, type=string, max_limit=500)

A human-readable version of the band name. This can contain any characters (up to the character limit).

start_wave_ang(required=True, type=string, max_limit=100)

A wavelength for the start of the filter bandpass of the image - in Angstrom. This is required by the Simple Image Access service.

central_wave_ang(required=True, type=string, max_limit=100)

A rough central wavelength of the image - in Angstrom. This is used to order the bands in the Image Cutout service options.

end_wave_ang(required=True, type=string, max_limit=100)

A wavelength for the end of the filter bandpass of the image - in Angstrom. This is required by the Simple Image Access service.

spatial_res(required=True, type=string, max_limit=100)

The spatial resolution (FWHM) of the image - in arcsec. This is required by the Simple Image Access service.

start_time(required=True, type=string, max_limit=100)

The start time of the image observation in UTC isoformat: yyyy-mm-ddThh:mm:ss.ss. In case of mosaics made of multiple images, this may either be left blank or preferably correspond to the start time of the earliest image in the mosaic. This is required by the Simple Image Access service.

end_time(required=True, type=string, max_limit=100)

The end time of the image observation in UTC isoformat: yyyy:mm:ddThh:mm:ss.ss. In case of mosaics made of multiple images, this may either be left blank or preferably correspond to the end time of the latest image in the mosaic. This is required by the Simple Image Access service.

pol_state(required=True, type=string, max_limit=100)

The polarization state(s) of the image. An empty string if irrelevant (e.g. optical data), otherwise a space-separated string consisting of one or more of the following: I Q U V RR LL RL LR XX YY XY YX POLI POLA. This is required by the Simple Image Access service.

facility(required=True, type=string, max_limit=100)

The name of the facility (this must match a facility name from the <survey>_<datarelease>_facility_meta.txt file above).

description(required=True, type=string, max_limit=500)

A succinct paragraph describing the facility.

documentation(required=False, type=string, max_limit=1000)

If you would like formatted text to appear in the Schema Browser, you must supply a file in the docs/ directory. The file can be either plain text or markdown-formatted text (see Formatting for more info). This field is set to the name of the file. If you do not wish to supply documentation for a particular group, leave this entry blank. Remember that the documentation mentioned here is uneditable once the data are released. Documentation intended for public use and/or subject to change (e.g., with detailed descriptions of analysis or version update information) should be maintained by the survey teams in Data Central’s Documentation portal: Documentation Central.

contact(required=True, type=string, max_limit=500)

Format as: John Smith <john.smith@institute.org>

version(required=True, type=string, max_limit=100)

Band version as defined by the team e.g., v1.8.

file_name(required=True, type=string, max_limit=1000)

The filename of the FITS file you will be providing. Note, you can provide multiple files at the same wavelength by providing an entry per file.

region(required=True, type=string, max_limit=1000)

The name of the region for this file (e.g., g09, g12). You may choose to define this from the center RA of the image.

is_displayed(required=True, type=bool)

Y or N. If N, this row will be skipped on ingestion (you may wish to give us the metadata now and the file later).

Attention

The FITS header must contain the following keywords:

Keyword	Description
GAIN	Maximum equivalent gain (e-/ADU)
CD1_1	Linear projection matrix
CD1_2	Linear projection matrix
CD2_1	Linear projection matrix
CD2_2	Linear projection matrix
NAXIS	Number of axes
CRPIX1	Reference pixel on this axis
CRPIX2	Reference pixel on this axis
CRVAL1	World coordinate on this axis
CRVAL2	World coordinate on this axis
CTYPE1	WCS projection type for this axis
CTYPE2	WCS projection type for this axis
CUNIT1	Axis unit
CUNIT2	Axis unit
NAXIS1	Number of elements along this axis
NAXIS2	Number of elements along this axis
EQUINOX	Mean equinox
RADECSYS	Astrometric system