Namespace lsst::afw::geom::detail

namespace detail

Functions

std::shared_ptr<ast::FrameSet> readFitsWcs(daf::base::PropertySet &metadata, bool strip = true)

Read a FITS convention WCS FrameSet from FITS metadata

The resulting FrameSet may be any kind of WCS supported by FITS; if it is a celestial WCS then 1,1 will be the lower left corner of the image (the FITS convention, not the LSST convention).

This routine replaces RADECSYS with RADESYS if the former is present and the latter is not, since that is a common misspelling in FITS headers.

The returned FrameSet will have an IWC (intermediate world coordinate system) frame.

Parameters

  • [inout] metadata: FITS header cards

  • [in] strip: If true: strip items from metadata used to create the WCS, such as RADESYS, EQUINOX, CTYPE12, CRPIX12, CRVAL12, etc. Always keep keywords that might be wanted for other purpposes, including NAXIS12 and date-related keywords such as “DATE-OBS” and “TIMESYS” (but not “EQUINOX”).

Exceptions

  • pex::exceptions::TypeError: if the metadata does not contain a FITS-WCS

std::shared_ptr<ast::FrameDict> readLsstSkyWcs(daf::base::PropertySet &metadata, bool strip = true)

Read an LSST celestial WCS FrameDict from a FITS header.

Calls getImageXY0FromMetadata to determine image XY0.

Saves CRVAL by setting the output SkyFrame’s SkyRef to CRVAL and SkyRefIs=”Ignore” (so SkyRef is not treated as an offset).

The frames of the returned WCS will be as follows:

  • ”PIXELS” (base frame): pixel frame with 0,0 the lower left corner of the image (LSST convention)

  • ”IWC”: FITS WCS intermediate world coordinate system

  • ”SKY” (current frame): an ast::SkyFrame with domain “SKY”: ICRS RA, Dec

Warning

Does not compensate for the offset between a subimage and its parent image; callers must do that manually, e.g. by calling SkyWcs::copyAtShiftedPosition.

Warning

the general SkyWcs generated by LSST software cannot be exactly represented using standard WCS FITS cards, and so this function cannot read those. This function is intended for two purposes:

  • Read the standard FITS WCS found in raw data and other images from non-LSST observatories and convert it to the LSST pixel convention.

  • Read the approximate FITS WCS that LSST writes to FITS images (for use by non-LSST code).

All frames are instances of ast::Frame except the SKY frame. All have 2 axes.

Parameters

  • [inout] metadata: FITS header cards

  • [in] strip: If true: strip items from metadata used to create the WCS, such as RADESYS, EQUINOX, CTYPE12, CRPIX12, CRVAL12, etc. Always keep keywords that might be wanted for other purpposes, including NAXIS12 and date-related keywords such as “DATE-OBS” and “TIMESYS” (but not “EQUINOX”).

Exceptions

  • lsst::pex::exceptions::TypeError: if the metadata does not describe a celestial WCS.

std::shared_ptr<daf::base::PropertyList> getPropertyListFromFitsChan(ast::FitsChan &fitsChan)

Copy values from an AST FitsChan into a PropertyList

Warning

COMMENT and HISTORY cards are treated as string values

Exceptions

  • lsst::pex::exceptions::TypeError: if fitsChan contains cards whose type is not supported by PropertyList: complex numbers, or cards with no value

ast::FitsChan getFitsChanFromPropertyList(daf::base::PropertySet &metadata, std::set<std::string> const &excludeNames = {}, std::string options = "")

Construct AST FitsChan from PropertyList

Return

an ast::FitsChan representing this PropertyList

Parameters

  • [in] metadata: Metadata to transfer; if this is a PropertyList then the order of items is preserved.

  • [in] excludeNames: Names of entries to exclude from the returned header string.

  • [in] options: Options string to pass to ast::FitsChan constructor.

template<class Transform>
std::shared_ptr<Transform> readStream(std::istream &is)

Deserialize a Transform from an input stream

Template Parameters

  • Transform: the Transform class; can be Transform<FromEndpoint, ToEndpoint>, SkyWcs, or any other compatible class, i.e. it must support the following (see Transform.h for details):

    • a constructor that takes an ast::FrameSet

    • static method getShortClassName

    • method getMapping

Parameters

  • [in] is: input stream from which to deserialize this Transform

template<class Transform>
void writeStream(Transform const &transform, std::ostream &os)

Serialize a Transform to an output stream

Version 1 format is as follows:

  • The version number (an integer)

  • A space

  • The short class name, as obtained from getShortClassName

  • A space

  • The contained ast::FrameSet written using FrameSet.show(os, false)

Parameters

  • [out] os: output stream to which to serialize this Transform

  • [in] transform: Transform to serialize

Variables

constexpr int serializationVersion = 1

version of serialization used when writing (older versions may also be supported when reading)