LSST Data Management UML Domain Model LDM-133 Latest Revision 10/10/2013
Large Synoptic Survey Telescope (LSST)
Data Management UML Domain Model
Mario Juric, Kian-Tat Lim, Jeff Kantor
Latest Revision: October 10, 2013
This LSST document has been approved as a Content-Controlled Document by the LSST DM Technical Control Team. If this document is changed or superseded, the new document will retain the Handle designation shown above. The control is on the most recent digital document with this Handle in the LSST digital archive and not printed versions. Additional information may be found in the LSST DM TCT minutes.
Updated to reflect model base on Data Challenge 3
Updated to reflect model base on Data Challenge 3B PT 1
FDR Prep (revision 1.128)
FDR Prep-Remove extra fields; add SDQA (revision 1.143); TCT approved
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Data Management UML Domain Model
Table of Contents
Change Record i
|2||DMS Domain Classes 8|
|2.1||Archive and Data Releases 11|
|2.1.1||Current or up-to-date data 12|
|2.1.2||Data Release 12|
|2.1.3||Engineering and Facility Database 12|
|2.1.4||Level 3 Data 13|
|2.1.5||Science Data Archive 13|
|2.2.2||Astrometric Standard 15|
|2.2.3||DIA Object 1|
|2.2.5||Light Curve 15|
|2.2.7||Photometric Standard 15|
|2.2.8||Solar System Object 15|
|2.2.9||Spectral Energy Distribution 15|
|2.2.10||Spectral Standard 15|
|2.2.11||Time Series 16|
|2.3.1||Aperture Correction 19|
|2.3.2||Arc Exposure 19|
|2.3.3||Astrometric Model 19|
|2.3.4||Atmospheric Measurement 19|
|2.3.5||Atmospheric Model 19|
|2.3.6||Atmospheric Numerical Model 19|
|2.3.7||Auxiliary Telescope Exposure 19|
|2.3.8||Auxiliary Telescope Spectrum 20|
|2.3.9||Barometric Pressure Measurement 20|
|2.3.10||Bias Exposure 20|
|2.3.11||Broadband Flat Exposure 20|
|2.3.12||Calibration Database 20|
|2.3.13||Calibration Exposure 20|
|2.3.14||Calibration Product 20|
|2.3.15||Crosstalk Correction Matrix 20|
|2.3.16||Dark Exposure 20|
|2.3.17||GPS PWV Measurement 21|
|2.3.18||Illumination Correction 21|
|2.3.19||Instrument Model 21|
|2.3.20||Master Bias Exposure 21|
|2.3.21||Master Broadband Flat Exposure 21|
|2.3.22||Master Calibration Exposure 21|
|2.3.23||Master Dark Exposure 21|
|2.3.24||Master Flat-Spectrum Flat Exposure 22|
|2.3.25||Master Fringe Exposure 22|
|2.3.26||Master Illumination Correction 22|
|2.3.27||Master Pupil Ghost Exposure 22|
|2.3.28||Microwave Radiometer Measurement 22|
|2.3.29||Monochromatic Dome Flat Exposure 22|
|2.3.30||Nightly Flat Exposure 22|
|2.3.31||Optical Ghost Catalog 22|
|2.3.32||Optical Model 23|
|2.3.33||Photometric Model 23|
|2.3.34||Photometric Parameters 23|
|2.3.35||Photometric Zero Point 23|
|2.3.36||Pupil Ghost Exposure 23|
|2.3.37||Raw Calibration Exposure 23|
|2.3.38||Scattered Light Model 24|
|2.3.39||Spectrum Exposure 24|
|2.3.40||Star Raster Scan Exposure 24|
|2.3.41||System Bandpass 24|
|2.3.42||Telescope Bandpass Model 24|
|2.3.44||Domain Model - Calibration Exposures 24|
|2.4.3||Defect Map 26|
|2.4.5||Distortion Map 26|
|2.4.6||Electrical Geometry 26|
|2.4.7||Focal Plane Array 26|
|2.4.8||Imaging Region 26|
|2.4.9||Monolithic Detector 27|
|2.4.10||Overscan Columns 27|
|2.4.11||Physical Geometry 27|
|2.5.2||AstroObject Catalog 30|
|2.5.3||Astrometric Reference Catalog 30|
|2.5.4||Aux Telescope Spectrum Catalog 30|
|2.5.6||DIA Object Catalog 31|
|2.5.7||DIA Source Catalog 31|
|2.5.8||Data Product 31|
|2.5.9||Exposure Catalog 31|
|2.5.10||External Catalog 31|
|2.5.11||Forced DIA Source Catalog 31|
|2.5.12||Forced Source Catalog 31|
|2.5.13||Level 1 Catalog 31|
|2.5.14||Level 2 Catalog 31|
|2.5.15||Photometric Standards Catalog 32|
|2.5.16||Sky Coverage Map 32|
|2.5.17||Solar System Object Catalog 32|
|2.5.18||Solar System Object Reference Catalog 32|
|2.5.19||Source Catalog 32|
|2.5.20||Spectral Standards Catalog 32|
|2.5.21||Standard Catalogs 32|
|2.5.22||Domain Model - Level 1 Catalog 32|
|2.5.23||Domain Model - Level 2 Catalog 33|
|2.6.2||Coordinate Transform 33|
|2.6.3||Image Plane Coordinate 33|
|2.6.4||Sky Coordinate 33|
|2.7.1||Calibrated Exposure 35|
|2.7.2||Coadded Exposure 35|
|2.7.3||Deep Coadded Exposure 36|
|2.7.4||Detection Efficiency Map 36|
|2.7.5||Difference Exposure 36|
|2.7.7||Exposure Stack 37|
|2.7.9||Observation Metadata 37|
|2.7.10||Observing Filter 37|
|2.7.12||Raw Exposure 38|
|2.7.13||Shutter Timing 38|
|2.7.14||Sky Background Model 38|
|2.7.15||Template Exposure 38|
|2.8.4||Pixel Coordinates 40|
|2.8.5||Postage Stamp 40|
|2.8.6||Variance Image 40|
|2.9.1||Mask Plane 41|
|2.10.1||Adaptive Moments 45|
|2.10.2||Aperture Flux 45|
|2.10.3||Astrometric Measurement 45|
|2.10.5||Dipole Source Model 45|
|2.10.6||Extended Source Model 45|
|2.10.7||Flux Variability Model 45|
|2.10.9||PSF Flux 46|
|2.10.10||Photometric Measurement 46|
|2.10.11||Point Source Model 46|
|2.10.12||Proper Motion Model 47|
|2.10.13||Shape Measurement 47|
|2.10.14||Standard Color 47|
|2.10.15||Surface Brightness Profile 47|
|2.10.16||Trailed Source Model 47|
|2.11.1||Field of View 48|
|2.11.3||Sky Projection 48|
|2.11.4||Sky Region 48|
|2.11.5||Sky Tessellation 49|
|2.11.6||Sky Tile 49|
|2.12.1||Coadd Source 50|
|2.12.2||Cosmic Ray 50|
|2.12.3||DIA Source 50|
|2.12.5||Forced DIA Source 51|
|2.12.6||Forced Source 51|
|2.12.7||Optical Ghost 51|
|2.13||Transient Alerts 51|
|2.13.1||Moving Object Alert 52|
|2.13.2||Transient Alert 52|
|2.13.3||Transient Alert Broker 52|
|2.13.4||Variable Object Alert 53|
|The Purpose of this Document is to define the Domain Model for the LSST Data Management System (DMS). This document is generated from Enterprise Architect.|
2 DMS Domain Classes
The DMS Domain Classes represent the DMS data products and their relationships to each other. They are captured on UML Class Diagrams, which depict the classesa and several types of relationships.
In each of these relationships two classes are connected by a line representing the relationship. In each case, the "target" class has a symbol (triangle, diamond, etc.) on end of the graphic connector attached to it, while the "source" class has no symbol on the end of the connector. The relationships shown are:
Generalization/Specialization (solid line, triangle at target) - The source class is a subclass or more specialized version of the more generalized target class. This is also referred to in slang as an "is a" relationship.
Aggregation (solid line, diamond at target) - The source class is a component or part of the larger, more complicated target class. This is also referred to in slang as a "has a" relationship.
Dependency (dashed line, simple arrowhead at target) - The source class depends on the target class in some way, typically using some attribute or service of the target class. This can also be used between packages to show dependencies between contents of a package on contents of another package.
Association (solid line, no end symbols) - The two classes are associated by some other relationship, typically a processing input/output relationship.
In addition to the Class Diagrams, each class on the diagrams is further defined in structured text, in alphabetically sorted paragraphs immediately following the diagram.
Finally, as there are many classes, they have been packaged into categories of most closely related classes, e.g. Catalogs.
This diagram depicts the packages in the DMS Domain Model.
2.1 Archive and Data Releases
This package contains classes associated with the global level archived and released data products.
This diagram depicts the Science Data Archive, the main repository of DMS data products. It shows a parallel relationship to the Engineering and Facility database, which contains meta-data about the LSST System and about the images contained within the Science Data Archive. The Science Data Archive contains repositories of Transient Alerts, Images, and Catalogs, each of which is further described in a package of that name. The contents of the Science Data Archive are organized into Data Releases.
2.1.1 Current or up-to-date data
Recently acquired data which has not been incorporated into a Data Release.
2.1.2 Data Release
The public release of the full set of data products that are obtained from the systematic re-processing and uniform calibration of the entire survey, released on a regular schedule (e.g., annual).
DPDD - Over 10 years of operations, LSST will produce eleven data releases: two for the first year of survey operations, and one every subsequent year. Each data release will include reprocessing of all data from the start of the survey, up to the cutoff date for that release.contents of data releases include the raw images, retained coadds, and catalogs. Given the scale, it is not feasible to keep all data releases loaded and accessible at all times, only the contents of the most recent data release, and the penultimate data release will be kept on fast storage and with catalogs loaded into the database. Statistics collected by prior surveys (eg., SDSS) show that users nearly always prefer accessing the most recent data release, but sometimes may use the penultimate one (this is especially true just after the publication of a new data release). Older releases are used rarely, to assist with data quality monitoring and assessment small, overlapping, samples of data from older releases will be kept loaded in the database. The sample size is expected to be on order of 1 - 5% of the data release data, with larger samples kept early on in the survey. The goal is to allow one to test how the reported characterization of the same data varies from release to release. Releases will be archived to mass storage (tape). The users will not be able to perform database queries against archived releases. They will be made available as bulk downloads in some common format (for example, FITS binary tables). Database software and data loading scripts will be provided for users who wish to set up a running copy of an older (or current) data release database on their systems.raw data used to generate any public data product (raw exposures, calibration frames, telemetry, configuration metadata, etc.) will be kept and made available for download.
2.1.3 Engineering and Facility Database
A database containing telemetry and other meta-data about the LSST System and the images taken with the Camera. It also contains a record of all commands. This database is created and managed by the Observatory Control System (OCS). The DMS archives and accesses the EFD for processing and query purposes, and populates the EFD (via OCS) with data quality information and DMS status.
2.1.4 Level 3 Data
Data products generated by users on any computing resources anywhere that are brought to an LSST Data Access Center (DAC), stored there, and federated with Level 1 and Level 2 data.
2.1.5 Science Data Archive
The main repository of DMS data products. Contains repositories of Transient Alerts, Images, and Catalogs, each of which is further described in a package of that name. Also note the the contents of the Science Data Archive are organized into Data Releases.
This package contains classes associated with astronomical object data products.
Figure 3: Domain Model - AstroObjects
This diagram depicts AstroObject, the core class representing celestial objects such as Galaxies, Stars, Solar System Objects, etc. The objects are characterized as aggregates, by what sort of information about them is relevant and captured in the DMS (e.g. Light Curve), and by specializations according to the role that the object plays in DMS processing (e.g. Astrometric Standard).
A representation of an astronomical object for which the astrophysical properties have or will be characterized from LSST data, or an externally derived astronomical object whose astrophysical properties will be used in LSST data processing.
It does not necessarily have to have coordinates associated to it (e.g., if it is a Solar System Object, it only has an Orbit).
2.2.2 Astrometric Standard
An AstroObject (usually a star) utilized for Astrometric calibration.
2.2.3 DIA Object
A representation of an astronomical object, in particular its astrophysical properties as derived from analysis of the DIA Sources that are associated with it.
A Time Series of predicted Sky Coordinates for a Solar System Object.
2.2.5 Light Curve
A Time Series of magnitude or flux in a given Observing Filter vs Time
A six parameter set of orbital elements, and associated covariance matrix, that specifies the orbit of a Solar System Object
2.2.7 Photometric Standard
An AstroObject (usually a star) utilized for photometric calibration. It has been determined to be non-variable, and may have an associated SED.
2.2.8 Solar System Object
An AstroObject representing asteroids and other objects within the Solar System.
2.2.9 Spectral Energy Distribution
Arbitrarily normalized flux as a function of wavelength.
2.2.10 Spectral Standard
An AstroObject with an accurately known SED, intended as an observing target of the Auxiliary Telescope.
2.2.11 Time Series
A series of values of a quantity obtained at successive times.
Most frequently, the quantity is Flux , but can be anything (e.g., coordinates)
This package contains classes associated with calibration data products.
Figure 4: Domain Model - Calibration Products
Figure 5: Domain Model - Calibration Exposures
Figure 6: Domain Model - Photometric Calibration
Figure 7: Domain Model - Astrometric Calibration
2.3.1 Aperture Correction
Correction for the finite size of the aperture over which a Source's flux is being measured.
2.3.2 Arc Exposure
An Exposure of a source with a known spectrum (usually an arc lamp) taken by the Auxiliary Telescope.
Used to calibrate spectra taken by the Auxiliary Telescope.
2.3.3 Astrometric Model
The Astrometric Model is a high-fidelity, bidirectional Coordinate Transform between Image Plane Coordinates and Sky Coordinates. A variety of mappings is possible, including ones that are color dependent and nonlinear.
The transformation may dependent on the color (or SED) of the object presumed to have been observed at the given Image Plane Coordinates.
2.3.4 Atmospheric Measurement
A measurement pertaining to the state of the atmosphere at LSST observatory site.
2.3.5 Atmospheric Model
This is a model derived from Atmospheric Measurements which gives atmospheric extinction as function of wavelength and position for a given Exposure.
2.3.6 Atmospheric Numerical Model
A numerical model of the Atmosphere, such as a MODTRAN model, which gives physical properties as a function of spatial position, and can generate extinction and emission as a function of wavelength for any altitude and azimuth and time within the night for which it was constructed.
2.3.7 Auxiliary Telescope Exposure
2.3.8 Auxiliary Telescope Spectrum
A spectrum (flux vs wavelength) of a Spectral Standard taken with the Observatory's Auxiliary Telescope.
2.3.9 Barometric Pressure Measurement
The measurement of barometric pressure at the Telescope.
2.3.10 Bias Exposure
An zero-length Exposure taken with a closed shutter. Used to calibrate out the bias.
2.3.11 Broadband Flat Exposure
An Exposure of the dome screen illuminated with broadband light. Used to perform flat field correction.
2.3.12 Calibration Database
Database containing all Calibration Data and Calibration Products.
2.3.13 Calibration Exposure
An Exposure acquired and/or used for purposes of calibration.
2.3.14 Calibration Product
A Data Product used by the Data Management System to perform astrometric or photometric calibration of data.
Raw data, explicitly taken for the purpose of aiding calibration, is included in this definition.
2.3.15 Crosstalk Correction Matrix
A matrix of coefficients representing corrections that need to be applied during processing of images to remove crosstalk signal between CCDs.
2.3.16 Dark Exposure
An Exposure of the same length as a Raw Exposure it's designed to calibrate, taken with a closed shutter. Used for dark current subtraction.
2.3.17 GPS PWV Measurement
An all-sky measurement of precipitable water vapor (PWV) column, obtained by the GPS system.
2.3.18 Illumination Correction
The ratio between an ideal photometric flat field obtained by a raster scan across the field of a collimated light source at infinity, and the observed flat field.
Wavelength and focal plane position dependent (a data cube)
2.3.19 Instrument Model
Contains all information required to convert a photon flux in a ray from given angular coordinates wrt the Camera optical axis into ADU counts/sec in the corresponding Pixels.
2.3.20 Master Bias Exposure
A high fidelity Exposure created from Bias Exposures and other data, to be used for bias substraction.
2.3.21 Master Broadband Flat Exposure
A high fidelity flat field Exposure created from Broadband Flat Field Exposures and other data. Used for flat field correction (on the Auxiliary Telescope) and .
2.3.22 Master Calibration Exposure
An Exposure created from Raw Calibration Exposures and other data to be used in calibration processing, designed to have higher fidelity (usually, signal-to-noise ration) than the input data.
2.3.23 Master Dark Exposure
An high fidelity Exposure created from Dark Exposures and other data, to be used for dark current subtraction.
2.3.24 Master Flat-Spectrum Flat Exposure
An Exposure created by a linear combination of Monocromatic Dome Flat Exposures, mimicking an Exposure of a dome screen uniformly illuminated by a light source with a flat, SED(\lambda) = const, spectrum.
2.3.25 Master Fringe Exposure
An Exposure created from Monochromatic Dome Flat Exposures and other data, to be used in defringing.
2.3.26 Master Illumination Correction
A high fidelity Illumination Correction model obtained by making a suitable combination of Illumination Correction models obtained by different methods.
2.3.27 Master Pupil Ghost Exposure
An Exposure created from Pupil Ghost Exposures and other data to be used in pupil ghost substraction.
2.3.28 Microwave Radiometer Measurement
A measurement of precipitable water vapor (PWV) column, obtained by a microwave radiometer co-pointed with the LSST telescope.
2.3.29 Monochromatic Dome Flat Exposure
An Exposure of the dome screen illuminated with monochromatic light, taken by main LSST Telescope. Used to construct broadband flats and fringe frames, and measure system bandpasses.
2.3.30 Nightly Flat Exposure
A flat field exposure appropriate for a night of observing.
2.3.31 Optical Ghost Catalog
A Catalog of Optical Ghosts present in the LSST Telescope.
2.3.32 Optical Model
Computational model of Telescope optics (provided by the Telescope & Site subsystem). It is used to create the Master Pupil Ghost Exposure and in Illumination Correction.
2.3.33 Photometric Model
The Photometric Model is a bidirectional mapping between instrumental magnitude and calibrated magnitude. A variety of mappings is possible, including ones that are spatially dependent and nonlinear.
For the nightly processing pipelines, a model of a single, constant, zero point per CCD may suffice.
2.3.34 Photometric Parameters
The collection of (typically fitted) parameters needed to evaluate the Photometric Model at some location.
The simplest example is a single, constant, photometric zero point.
2.3.35 Photometric Zero Point
The magnitude of an AstroObject whose flux generates one DN per second.
Given the zero point ZP and an instrumental magnitude minst, the magnitude of an object is computed as:
m = minst + ZP
2.3.36 Pupil Ghost Exposure
An Exposure of the image of the Telescope entrance pupil on the Focal Plane. Used in calibration of the main LSST Telescope data.
2.3.37 Raw Calibration Exposure
An Exposure taken by the Auxiliary Telescope or main LSST Telescope. Used in calibration of either the Auxiliary Telescope or the main LSST Telescope.
2.3.38 Scattered Light Model
2.3.39 Spectrum Exposure
An Exposure containing spectra of standard or atmospheric probe stars, taken by the Auxiliary Telescope. Used in calibration of main LSST Telescope data.
2.3.40 Star Raster Scan Exposure
An exposure of a dense but not crowed stellar field, designed to help with determination of Illumination Correction and Crosstalk Correction Matrix.
2.3.41 System Bandpass
The normalized system bandpass, as defined in the SRD.
Typically computed "on the fly" by combining the results of the Atmospheric Model and the Instrument Model.
2.3.42 Telescope Bandpass Model
The model of the variation of the combined Telescope and Camera normalized system bandpass as defined in the SRD with environmental parameters (e.g., temperature, pressure, etc.).
A function which maps Sky Coordinates to Image Plane Coordinates and vice versa.
It may or may not use the Sky Projections and conventions defined by the IAU WCS (Greisen & Calbretta) standard.
2.3.44 Domain Model - Calibration Exposures
This package contains classes associated with representations of the Camera sensors/detectors used in creating and processing DMS data products.
Figure 8: Domain Model - Detectors
This diagram depicts classes representing the geometry of the camera and sensors used in DMS processing.
A maximal Monolithic Detector, possibly with multiple Segments read out in parallel by the camera electronics.
An entity representing the LSST camera, including the Focal Plane Array and all read-out electronics.
2.4.3 Defect Map
The Defect Map is a catalog of defective pixels in the Detector, categorizing the type of defect as one of Hot, Dead, Trap, or Bad Column
A two dimensional surface capable of imaging, that is recording incident photon flux in an array of Pixels.
2.4.5 Distortion Map
A map of geometrical distortions of CCD pixels (location and shape).
2.4.6 Electrical Geometry
The Electrical Geometry specifies the order in which the Segment pixels are read out, including not only the physical imaging pixels, but also the overscan pixels that can be located before and/or after each row of physical pixels.
/* Not used by the use cases. Also may be incorrect: If the Segment is meant to represent the physical CCD, that CCD has no "Electrical Geometry" attached to it; I think it's a property of how it is read out (though it's likely it will not change often in operations). If so, Imaging Region and Overscan Columns should be attached to Exposure Metadata */
2.4.7 Focal Plane Array
An array of CCDs in the focal plane of the telescope, read out together by the camera electronics.
2.4.8 Imaging Region
The part of the Electrical Geometry that captures flux information in pixels as part of the image.
2.4.9 Monolithic Detector
A Detector which is associated with a monolithic substrate. This implies that the geometric relationships between pixels are fixed over the life of the Detector.
2.4.10 Overscan Columns
The part of the Electrical Geometry that captures pixels that can be located before and/or after each row of physical pixels.
2.4.11 Physical Geometry
A 3-dimensional Coordinate Transform between a Detector's Pixel Coordinates and Focal Plane Coordinates. This includes height offsets from the idealized Focal Plane
A rectangular, 3 x 3, set of CCDs sharing the same mechanical support structure within the Focal Plane Array.
/* NOTE: This definition needs improving */
A region of a CCD, read out into a data stream separate from those of other Segments. A Segment has a fixed geometrical relationship to the other Segments in the same CCD.
Often colloquially referred to as an 'Amplifier', as each Segment is read out by a separate amplifier.
This package contains classes associated with catalog data products.
Figure 9: Domain Model - Data Products
Figure 10: Domain Model - Catalogs
Figure 11: Domain Model - External Catalogs
Figure 12: Domain Model - Level 1 Catalog
Figure 13: Domain Model - Level 2 Catalog
A Catalog of AstroObjects.
2.5.2 AstroObject Catalog
2.5.3 Astrometric Reference Catalog
An external reference Catalog used for astrometric calibration.
2.5.4 Aux Telescope Spectrum Catalog
A complete list of items in some systematic order. May include the items themselves.
Usually realized as one or more relational database tables, or a database with large objects stored as files on disk.
2.5.6 DIA Object Catalog
A Catalog of DIA Objects.
2.5.7 DIA Source Catalog
A Catalog of DIA Sources.
2.5.8 Data Product
An article of data made to be served to LSST users.
2.5.9 Exposure Catalog
A Catalog of all Exposures taken with LSST Telescope and the Auxiliary Telescope.
2.5.10 External Catalog
A Catalog of AstroObjects created external to LSST.
2.5.11 Forced DIA Source Catalog
A Catalog of Forced DIA Sources.
2.5.12 Forced Source Catalog
A Catalog of Forced Sources measured at positions determined from the AstroObject Catalog.
2.5.13 Level 1 Catalog
A Catalog collecting data produced in Level 1 (nightly) data processing.
These are largely data resulting from Difference Image Analysis.
2.5.14 Level 2 Catalog
A Catalog collecting Data Products produced in Level 2 data processing, and released as part of annual Data Releases.
2.5.15 Photometric Standards Catalog
An external reference Catalog used for photometric calibration.
2.5.16 Sky Coverage Map
A Data Product (function) with information on which areas of the sky were covered by the LSST survey, how many times, and to what limiting magnitude.
Useful when computing selection functions.
2.5.17 Solar System Object Catalog
A Catalog of Solar System Objects.
2.5.18 Solar System Object Reference Catalog
Externally created catalog of Solar System Objects.
Typically used to identify DIA Sources due to Solar System Objects.
2.5.19 Source Catalog
A Catalog of Sources detected and measured on Calibrated Images from LSST Visits.
2.5.20 Spectral Standards Catalog
An external Catalog of Spectral Standards, AstroObjects with well known SEDs used to monitor the state of the atmosphere.
2.5.21 Standard Catalogs
Catalogs of AstroObjects that are externally developed and used as a reference for Measurements or calibration.
2.5.22 Domain Model - Level 1 Catalog
2.5.23 Domain Model - Level 2 Catalog
Figure 14: Domain Model - Coordinates
A group of numbers used to indicate the position of some entity.
2.6.2 Coordinate Transform
A function that maps Coordinate from one two dimensional space to those of another.
2.6.3 Image Plane Coordinate
Coordinate in an ideal image plane, for example a tangent plane.
2.6.4 Sky Coordinate
A two-dimensional coordinate of a point on the celestial sphere, most frequently in Equatorial Coordinate System.
This package contains classes associated with exposures, which are aggregates of images and image-related data.
Figure 15: Domain Model - Exposures
This diagram depicts Exposures, the unit of processing for Alerts and Data Releases. Exposure is an aggregate of outputs of several processing steps, including a MaskedImage, WCS, PSF, etc.
There are several types of Exposure, including Raw Exposure, Coadded Exposure, Difference Exposure, etc.
2.7.1 Calibrated Exposure
An Exposure which has been transformed from a Raw Exposure to a pixel format that includes only the Imaging Region.
The processing will generally include removing the instrumental signature, adding Exposure components such as a WCS and PSF, and performing Photometric Calibration.
(This was formerly know as Processed Exposure)
2.7.2 Coadded Exposure
An Exposure which has been produced from an Exposure Stack by resampling each to a common Sky Projection and combining the Pixels with a coaddition algorithm.
Several types of coadds will be created:
• A set of deep coadds. One deep coadd will be created for each of the ugrizy bands, plus a seventh, deeper, multi-color coadd. These coadds will be optimized for a reasonable combination of depth (i.e., employ no PSF matching) and resolution (i.e., visits with significantly degraded seeing may be omitted). Transient sources (including Solar System objects, explosive transients, etc), will be removed. Care will be taken to preserve the astrophysical backgrounds.coadds will be kept indefinitely and made available to the users.primary purpose is to enable the end-users to apply alternative object characterization algorithms, perform studies of diffuse structures, and for visualization.
• A set of short-period coadds. These will comprise of multiple (ugrizyM) sets of yearly and multi-year coadds. Each of these sets will be created using only a subset of the data, and otherwise share the characteristics of the deep coadds described above. These are designed to enable detec- tion of long-term variable or moving objects that would be “washed out” (or rejected) in full-depth coadds. We do not plan to keep and make these coadds available. We will retain and provide sufficient metadata for users to re-create them using Level 3 or other resources.
• A set of best seeing coadds. One deep coadd will be created for each of the ugrizy bands, using only the best seeing data (for example, using only the first quartile of the realized seeing distribution). These will be built to assist the deblending process. We do not plan to keep and make these coadds available. We will retain and provide sufficient metadata for users to re-create them using Level 3 or other resources.
• One (ugrizyM) set of PSF-matched coadds. These will be used to measure colors and shapes of objects at “standard” seeing. We do not plan to keep and make these coadds available. We will retain and provide sufficient metadata for users to re-create them using3 or other resources.
2.7.3 Deep Coadded Exposure
A Coadded Exposure designed to maximize coadd depth, built with close to all available epochs.
2.7.4 Detection Efficiency Map
A map of Source detection efficiency.
2.7.5 Difference Exposure
An Exposure created from the difference of two Exposures.
Most frequently, it will be a difference of a Calibrated Exposure from a Visit, and a Template Exposure.
One or more MaskedImages in association with a variety of classes that add further information associated with the history of the MaskedImage (Observation MetaData), or derived through processing of the MaskedImage (e.g. WCS, Background Model, etc.).
Exposure optional metadata includes:
- Information about the detector (CCD and its amplifiers)
- Photometric zeropoint
- Filter information
- A PSF model
Calibration of raw data produces a Calibrated Exposure.
2.7.7 Exposure Stack
A set of associated Exposures.
When used in the context of building coadds, all are associated (and expected to overlap) the same Tract or Patch.
The FPAExposure is to a full Focal Plane Array (FPA) what an Exposure is to a single element of an FPA. It aggregates the Exposures of all, or a subset of, the imaging elements of the FPA. Additionally, it may have FPA spanning representations of the WCS and PSF.
2.7.9 Observation Metadata
Information that specifies the condition of the telescope, camera, and the environment, when the associated MaskedImage was acquired.
2.7.10 Observing Filter
The wavelength-dependent filter placed in front of the Focal Plane Array during the Exposure
The Point Spread Function, or PSF is a representation of the point spread function as a function of position in the associated MaskedImage.
The implementation shall include convenient summary information, like the FWHM or ellipticity. It will be possible to realize an Image of the PSF, given a coordinate within an image.
/* OLD: Mathematically, the PSF will be represented by a Kernel. This allows the PSF to be generated at any desired point within the MaskedImage extent. In addition, the PSF needs to include convenient summary info, like FWHM and ellipticity. */
2.7.12 Raw Exposure
An Exposure whose pixel format is that of the raw Detector readout, including prescan and overscans rows or columns.
A Raw Exposure will be delivered by the Camera in crosstalk-corrected form.
2.7.13 Shutter Timing
Function specifying the location of the edge of the shutter during shutter opening and closing, as a function of time.
2.7.14 Sky Background Model
A function returning the estimated sky background value in the Exposure as a function of pixel coordinates.
2.7.15 Template Exposure
A Coadded Exposure intended for use in image differencing.
Typically created by coadding some number of Exposures with appropriate outlier rejection to eliminate cosmic rays and astrophysical transients.
A Visit is a set of FPAExposures taken sequentially with the same telescope pointing.
This package contains classes associated with image data products.
Figure 16: Domain Model - MaskedImages
This diagram depicts classes associated with MaskedImages, showing them as aggregates of pixels.
Image is a simple collection of pixels.
- dimension (size);
- XY0: the position of the lower left-hand corner with respect to a parent Image, if any.
Capabilities of the object representing it in computer programs will include:
- fast iteration over pixels
- shared views of subregions (to avoid copying pixels); one can also make copies of subregions when needed
- save to and load from FITS files
- inline (fast) translation between pixel index and pixel position (position is a floating point value used to evaluate WCS, spatial models, etc.)
A MaskedImage contains an Image, a Variance Image, and a Mask, all of the same dimensions.
The Variance Image pixel value gives the estimated variance in the pixel value of the corresponding pixel of the Image.
The Mask pixel value is interpreted as a stack of bits, each of which describes some property of the corresponding Image pixel, with semantics given by the definitions of the associated Mask Planes.
Capabilities of the implementation are the same as Image. Note that for MaskedImage, the variance and mask planes must be propagated and handled appropriately in all operations (additions, convolutions, etc.).
The smallest addressable element of an Image.
2.8.4 Pixel Coordinates
Coordinates of a Pixel.
2.8.5 Postage Stamp
A small MaskeImage usually intended to depict an observation of an AstroObject.
There are multiple types of Postage Stamps depending on which type of Exposure it was extracted from (e.g. Difference Exposure, Calibrated Exposure, etc.)
2.8.6 Variance Image
An Image whose Pixel values store the variance of the corresponding Pixel value of an associated, identically sized, Image.
This package contains classes associated with masks needed to process image data products.
Figure 17: Domain Model - Masks
This diagram depicts classes that provide masking information about pixels on images. This information is used to convey information about cosmic rays, saturated pixels, satellite trails, etc. appearing in the image.
2.9.1 Mask Plane
A conceptual two-dimensional 1-bit Image where each pixel corresponds to a specific flag.
- BAD: Associated Pixel is known to be bad on the detector
- SAT: Associated Pixel was saturated on the detector
- CR: Associated Pixel is affected by a cosmic ray
- EDGE: Associated Pixel has no data, e.g. off the edge of a warped exposure
- INTERP: the value of the associated Pixel was interpolated using adjacent Pixels (typically true for BAD, SAT and CR pixels)
An Image whose Pixel values store sets of bits, packed to integers, meant to be interpreted as flags associated with the corresponding Pixel value of an associated, identically sized, Image.
/* OLD: Mask is a three dimensional array of bits, arranged as a stack of two dimensional Mask Planes. When a Mask is associated with a compatibly sized Image, each plane idenitifies the per-pixel presence or absence of a particular condition in the associated Image. */
Figure 18: Coadded Exposure Measurements
Figure 19: Difference Exposure Measurements
Figure 20: Exposure Stack Measurements
Figure 21: Measurements
Figure 22: Single Frame Measurements
2.10.1 Adaptive Moments
Measurement of adaptive moments (Bernstein & Jarvis, 2002)
2.10.2 Aperture Flux
A measurement of flux enclosed in one or more concentric apertures centered on a Source or AstroObject (e.g. Kron, Petrosian, etc. fluxes).
2.10.3 Astrometric Measurement
Properties that specify the position of a Source in the focal plane, and possibly the sky plane.
When measured for a Source, the position will always have at least an x- and y-pixel coordinates, but may have additional attributes.
The center point of the object as determined by a centroiding algorithm.
2.10.5 Dipole Source Model
A Measurement that characterizes properties of a Source having a positive and negative lobe in a Difference Exposure.
Primarily used to detect image subtraction artifacts.
2.10.6 Extended Source Model
A Measurement designed to fit characteristics of extended Sources or AstroObjects (for example, a bulge-disk double Sersic profile fit).
2.10.7 Flux Variability Model
A Measurement to characterize the observed flux variability of an AstroObject. Will consist of a set of variability metrics designed to characterize both periodic and non-periodic Light Curve behavior (e.g., Richards et al. 2011).
A measured property of a Source or an AstroObject.
A Measurement performed by LSST is a result of applying a particular measurement algorithm to the pixel data in the Footprint, or set of Footprints, that are associated with the Source or the AstroObject.
There may be multiple Measurements (with different algorithms) of a particular Source property, such as a flux.
A Source may have any number of Measurements, each of which is a measurement of a property of the Source, such as flux, position, or shape.
Each Measurement is the result of applying a particular measurement algorithm to the pixel data in the footprint, or set of footprints, that are associated with the Source. There may be multiple Measurements (with different algorithms) of a particular Source property, such as a flux.
2.10.9 PSF Flux
The flux measured under the assumption that the AstroObject at a given, fixed, position in an Exposure is a point source.
2.10.10 Photometric Measurement
Properties of a Source or AstroObject that relate to its flux or flux difference.
2.10.11 Point Source Model
A Measurement that characterizes properties of movable point sources.
It accounts for astrometric motion due to at least proper motion and parallax.
2.10.12 Proper Motion Model
A model of motion of an AstroObject, whose parameters are derived by fitting a Time Series of Centroids.
Will typically account for parallax and proper motion, but may potentially have binary orbit parameters as well.
2.10.13 Shape Measurement
Properties of a Source or AstroObject that describe its shape.
The properties are specific to a shape model. For example, an elliptical shape model could have a major axis length, a minor axis length, and a position angle.
2.10.14 Standard Color
A seeing-independent measurement of a color of the AstroObject.
2.10.15 Surface Brightness Profile
A Measurement of the surface brightness profile of the Source or AstroObject, using one of the accepted prescriptions (e.g., Petrosian, Kron, etc.)
2.10.16 Trailed Source Model
A Measurement that characterizes properties of point sources moving rapidly enough to be trailed in an Exposure.
This package contains classes that represent the sky as needed for creating data products.
Figure 23: Domain Model - Sky
This diagram depicts classes that describe the sky in terms of tesselations, regions, and tiles used in DMS processing.
2.11.1 Field of View
Sky Region visible to the Telescope focal plane.
A non-overlapping Sky Region that is a sub-division of a Tract.
2.11.3 Sky Projection
A map projection, a parametrized, systematic transformation of the latitudes and longitudes of locations on the surface of the celestial sphere into locations on a plane.
Examples include the Gnomonic (tangential plane) projection, or Mercator projection, etc.
/* OLD: A function which maps arbitrary spherical Sky Coordinates onto a cartesian plane. */
2.11.4 Sky Region
An arbitrary polygonal region of the sky.
A Sky Region may contain all the Sky Tiles from a Sky Tessellation that have an overlap with the region.
2.11.5 Sky Tessellation
A regular partitioning of the spherical surface of the sky into Sky Tiles. Examples include HTM and HEALPix.
2.11.6 Sky Tile
An element of a Sky Tessellation. A Sky Tile may contain other Sky Tiles in a hierarchical way.
An example of this would be a triangle in HTM or a square in HEALPix.
One of a set of fixed Sky Regions that are constructed to provide overlapping coverage of the entire sky. The overlap margin is large enough to contain an entire Field of View.
Their primary use is to define the location and extent of Coadded Exposures.
This package contains classes associated with detecting and measuring sources of light, which are a form of catalog data product.
Figure 24: Domain Model - Sources
This diagram depicts classes associated with measuring sources of light in images.
2.12.1 Coadd Source
A Source measured in a Coadded Exposure.
2.12.2 Cosmic Ray
A Source that has been determined to be due to a cosmic ray.
Identified Cosmic Rays are kept only for data quality analysis purposes.
2.12.3 DIA Source
A Source measured in a Difference Exposure.
A group of, usually connected, Pixels on the Image identified by an algorithm as being potentially illuminated by the same AstroObject.
2.12.5 Forced DIA Source
A Forced Source measured on a Difference Exposure.
2.12.6 Forced Source
A Source measured with its position (centroid) held fixed.
Usually a measurement performed at a predicted or possible position of an AstroObject.
2.12.7 Optical Ghost
A Source present in an Exposure due to secondary reflections on optical surfaces in the Telescope and the Camera.
A representation of the Measurements done on a group of pixels in an Image.
Typically a detection of an AstroObject in an Image.
A Source that has been determined to be a trail of a moving object.
Identified Streaks are kept only for data quality analysis purposes.
2.13 Transient Alerts
This package contains classes associated with identification and characterization of transient events, and alerting on such events, which are data products.
Figure 25: Transient Alerts
This diagram depicts classes that are created as a part of Alert processing in the DMS.
2.13.1 Moving Object Alert
A Transient Alert alerting to a new DIA Source associated to an Solar System Object.
2.13.2 Transient Alert
A Transient Alert is a notification of the detection and characterization of a moving or variable AstroObject. Transient Alert includes Sky Coordinates, Measurements, and a Postage Stamp of the detected transient. Associated DIA Object characteristics, as well as all previous DIA Source measurements, are also a part of the Transient Alert.
Transients may be classified into subtypes, but full classification is beyond the scope of the DMS. The DMS will provide a classification indicating whether the transient is moving or a true variable, if possible.
2.13.3 Transient Alert Broker
A software system designed to filter and route streams of Transient Alerts, based on user-defined rules.
2.13.4 Variable Object Alert
A Transient Alert of an AstroObject whose flux has changed.
The contents of this document are subject to configuration control by the LSST DM Technical Control Team.