lsst.meas.algorithms.loadReferenceObjects Namespace Reference

Classes
class	_FilterCatalog
class	LoadReferenceObjectsConfig
class	ReferenceObjectLoader

Functions
	getFormatVersionFromRefCat (refCat)
	getRefFluxField (schema, filterName)
	getRefFluxKeys (schema, filterName)
	applyProperMotionsImpl (log, catalog, epoch)

Function Documentation

applyProperMotionsImpl()

lsst.meas.algorithms.loadReferenceObjects.applyProperMotionsImpl	(		log,
			catalog,
			epoch )

Apply proper motion correction to a reference catalog.

Adjust position and position error in the ``catalog``
for proper motion to the specified ``epoch``,
modifying the catalog in place.

Parameters
----------
log : `lsst.log.Log` or `logging.getLogger`
    Log object to write to.
catalog : `lsst.afw.table.SimpleCatalog`
    Catalog of positions, containing:

    - Coordinates, retrieved by the table's coordinate key.
    - ``coord_raErr`` : Error in Right Ascension (rad).
    - ``coord_decErr`` : Error in Declination (rad).
    - ``pm_ra`` : Proper motion in Right Ascension (rad/yr,
        East positive)
    - ``pm_raErr`` : Error in ``pm_ra`` (rad/yr), optional.
    - ``pm_dec`` : Proper motion in Declination (rad/yr,
        North positive)
    - ``pm_decErr`` : Error in ``pm_dec`` (rad/yr), optional.
    - ``epoch`` : Mean epoch of object (an astropy.time.Time)
epoch : `astropy.time.Time`
    Epoch to which to correct proper motion.

Definition at line 833 of file loadReferenceObjects.py.

def applyProperMotionsImpl(log, catalog, epoch):
    """Apply proper motion correction to a reference catalog.
 
    Adjust position and position error in the ``catalog``
    for proper motion to the specified ``epoch``,
    modifying the catalog in place.
 
    Parameters
    ----------
    log : `lsst.log.Log` or `logging.getLogger`
        Log object to write to.
    catalog : `lsst.afw.table.SimpleCatalog`
        Catalog of positions, containing:
 
        - Coordinates, retrieved by the table's coordinate key.
        - ``coord_raErr`` : Error in Right Ascension (rad).
        - ``coord_decErr`` : Error in Declination (rad).
        - ``pm_ra`` : Proper motion in Right Ascension (rad/yr,
            East positive)
        - ``pm_raErr`` : Error in ``pm_ra`` (rad/yr), optional.
        - ``pm_dec`` : Proper motion in Declination (rad/yr,
            North positive)
        - ``pm_decErr`` : Error in ``pm_dec`` (rad/yr), optional.
        - ``epoch`` : Mean epoch of object (an astropy.time.Time)
    epoch : `astropy.time.Time`
        Epoch to which to correct proper motion.
    """
    if "epoch" not in catalog.schema or "pm_ra" not in catalog.schema or "pm_dec" not in catalog.schema:
        log.warning("Proper motion correction not available from catalog")
        return
    if not catalog.isContiguous():
        raise RuntimeError("Catalog must be contiguous")
    catEpoch = astropy.time.Time(catalog["epoch"], scale="tai", format="mjd")
    log.info("Correcting reference catalog for proper motion to %r", epoch)
    # Use `epoch.tai` to make sure the time difference is in TAI
    timeDiffsYears = (epoch.tai - catEpoch).to(astropy.units.yr).value
    coordKey = catalog.table.getCoordKey()
    # Compute the offset of each object due to proper motion
    # as components of the arc of a great circle along RA and Dec
    pmRaRad = catalog["pm_ra"]
    pmDecRad = catalog["pm_dec"]
    offsetsRaRad = pmRaRad*timeDiffsYears
    offsetsDecRad = pmDecRad*timeDiffsYears
    # Compute the corresponding bearing and arc length of each offset
    # due to proper motion, and apply the offset.
    # The factor of 1e6 for computing bearing is intended as
    # a reasonable scale for typical values of proper motion
    # in order to avoid large errors for small values of proper motion;
    # using the offsets is another option, but it can give
    # needlessly large errors for short duration.
    offsetBearingsRad = numpy.arctan2(offsetsDecRad*1e6, offsetsRaRad*1e6)
    offsetAmountsRad = numpy.hypot(offsetsRaRad, offsetsDecRad)
    for record, bearingRad, amountRad in zip(catalog, offsetBearingsRad, offsetAmountsRad):
        record.set(coordKey,
                   record.get(coordKey).offset(bearing=bearingRad*geom.radians,
                                               amount=amountRad*geom.radians))
    # TODO DM-36979: this needs to incorporate the full covariance!
    # Increase error in RA and Dec based on error in proper motion
    if "coord_raErr" in catalog.schema:
        catalog["coord_raErr"] = numpy.hypot(catalog["coord_raErr"],
                                             catalog["pm_raErr"]*timeDiffsYears)
    if "coord_decErr" in catalog.schema:
        catalog["coord_decErr"] = numpy.hypot(catalog["coord_decErr"],
                                              catalog["pm_decErr"]*timeDiffsYears)

getFormatVersionFromRefCat()

lsst.meas.algorithms.loadReferenceObjects.getFormatVersionFromRefCat

(

refCat

)

"Return the format version stored in a reference catalog header.

Parameters
----------
refCat : `lsst.afw.table.SimpleCatalog`
    Reference catalog to inspect.

Returns
-------
version : `int`
    Format version integer.

Raises
------
ValueError
    Raised if the catalog is version 0, has no metadata, or does not
    include a "REFCAT_FORMAT_VERSION" key.

Definition at line 41 of file loadReferenceObjects.py.

def getFormatVersionFromRefCat(refCat):
    """"Return the format version stored in a reference catalog header.
 
    Parameters
    ----------
    refCat : `lsst.afw.table.SimpleCatalog`
        Reference catalog to inspect.
 
    Returns
    -------
    version : `int`
        Format version integer.
 
    Raises
    ------
    ValueError
        Raised if the catalog is version 0, has no metadata, or does not
        include a "REFCAT_FORMAT_VERSION" key.
    """
    errMsg = "Version 0 refcats are no longer supported: refcat fluxes must have nJy units."
    md = refCat.getMetadata()
    if md is None:
        raise ValueError(f"No metadata found in refcat header. {errMsg}")
 
    try:
        version = md.getScalar("REFCAT_FORMAT_VERSION")
        if version == 0:
            raise ValueError(errMsg)
        else:
            return version
    except KeyError:
        raise ValueError(f"No version number found in refcat header metadata. {errMsg}")
 
 

getRefFluxField()

lsst.meas.algorithms.loadReferenceObjects.getRefFluxField	(		schema,
			filterName )

Get the name of a flux field from a schema.

Parameters
----------
schema : `lsst.afw.table.Schema`
    Reference catalog schema.
filterName : `str`
    Name of camera filter.

Returns
-------
fluxFieldName : `str`
    Name of flux field.

Notes
-----
Return the alias of ``anyFilterMapsToThis``, if present
else, return ``*filterName*_camFlux`` if present,
else, return ``*filterName*_flux`` if present (camera filter name
matches reference filter name), else raise an exception.

Raises
------
RuntimeError
    Raised if an appropriate field is not found.

Definition at line 758 of file loadReferenceObjects.py.

def getRefFluxField(schema, filterName):
    """Get the name of a flux field from a schema.
 
    Parameters
    ----------
    schema : `lsst.afw.table.Schema`
        Reference catalog schema.
    filterName : `str`
        Name of camera filter.
 
    Returns
    -------
    fluxFieldName : `str`
        Name of flux field.
 
    Notes
    -----
    Return the alias of ``anyFilterMapsToThis``, if present
    else, return ``*filterName*_camFlux`` if present,
    else, return ``*filterName*_flux`` if present (camera filter name
    matches reference filter name), else raise an exception.
 
    Raises
    ------
    RuntimeError
        Raised if an appropriate field is not found.
    """
    if not isinstance(schema, afwTable.Schema):
        raise RuntimeError("schema=%s is not a schema" % (schema,))
    try:
        return schema.getAliasMap().get("anyFilterMapsToThis")
    except LookupError:
        pass  # try the filterMap next
 
    fluxFieldList = [filterName + "_camFlux", filterName + "_flux"]
    for fluxField in fluxFieldList:
        if fluxField in schema:
            return fluxField
 
    raise RuntimeError("Could not find flux field(s) %s" % (", ".join(fluxFieldList)))
 
 

getRefFluxKeys()

lsst.meas.algorithms.loadReferenceObjects.getRefFluxKeys	(		schema,
			filterName )

Return keys for flux and flux error.

Parameters
----------
schema : `lsst.afw.table.Schema`
    Reference catalog schema.
filterName : `str`
    Name of camera filter.

Returns
-------
keys : `tuple` of (`lsst.afw.table.Key`, `lsst.afw.table.Key`)
    Two keys:

    - flux key
    - flux error key, if present, else None

Raises
------
RuntimeError
    If flux field not found.

Definition at line 800 of file loadReferenceObjects.py.

def getRefFluxKeys(schema, filterName):
    """Return keys for flux and flux error.
 
    Parameters
    ----------
    schema : `lsst.afw.table.Schema`
        Reference catalog schema.
    filterName : `str`
        Name of camera filter.
 
    Returns
    -------
    keys : `tuple` of (`lsst.afw.table.Key`, `lsst.afw.table.Key`)
        Two keys:
 
        - flux key
        - flux error key, if present, else None
 
    Raises
    ------
    RuntimeError
        If flux field not found.
    """
    fluxField = getRefFluxField(schema, filterName)
    fluxErrField = fluxField + "Err"
    fluxKey = schema[fluxField].asKey()
    try:
        fluxErrKey = schema[fluxErrField].asKey()
    except Exception:
        fluxErrKey = None
    return (fluxKey, fluxErrKey)