Projection.h

Classes

Projection -- Geometric parameters needed for a sky projection to a plane (full description)

class Projection

Types

enum Type

AZP
Zenithal/Azimuthal perspective.

TAN
Gnomonic.

SIN
Orthographics/synthesis.

STG
Stereographic.

ARC
zenith/azimuthal equidistant.

ZPN
zenithal/azimuthal polynomial.

ZEA
zenithal/azimuthal equal area.

AIR
Airy.

CYP
Cylindrical perspective.

CAR
Cartesian.

MER
Mercator.

CEA
Cylindrical equal area.

COP
Conic perspective.

COD
Conic equidistant.

COE
Conic equal area.

COO
Conic orthomorphic.

BON
Bonne.

PCO
Polyconic.

SFL
Sanson-Flamsteed (global sinusoidal). The old GLS projection is now SFL. The 'GLS' string will be converted to 'SFL'

PAR
Parabolic.

AIT
Hammer-Aitoff.

MOL
Molweide.

CSC
COBE quadrilateralized spherical cube.

QSC
Quadrilateralized spherical cube.

TSC
Tangential spherical cube.

N_PROJ
N_PROJ gives the number of supported projections - it shouldn't be used as a projection

Interface

Public Members

Projection(Projection::Type which=CAR)

Projection(Projection::Type which, const Vector<Double> &parameters)

Projection(const Projection &other)

Projection &operator=(const Projection &other)

~Projection()

Projection::Type type() const

String name() const

static String name(Projection::Type proj)

static Projection::Type type(const String &name)

static uInt nParameters(Projection::Type proj)

const Vector<Double> &parameters() const

Bool near(const Projection &other, Double tol=1.0e-6) const

static Bool isZenithal (Projection::Type proj)

Private Members

void validate()

Description

Review Status

Reviewed By:

Peter Barnes

Date Reviewed:

1999/12/24

Programs:

Tests:

tProjection

Prerequisite

Knowledge of astronomical coordinate conversions in general. Probably the best documents are the papers by Mark Calabretta and Eric Greisen. The initial draft from 1996 can be found at http://www.atnf.csiro.au/~mcalabre. It is this draft that the Coordinate classes are based upon. Since then, this paper has evolved into three which can be found at the above address, and will be published in the Astronomy and Astrophysics Supplement Series (probably in 2000). The design has changed since the initial draft. When these papers are finalized, and the IAU has ratified the new standards, WCSLIB (Mark Calabretta's implementation of these conventions) will be revised for the new designs. At that time, the Coordinate classes may also be revised.

Synopsis

This class is used to hold:

The type of the projection (e.g. SIN); and
The parameters of the projection, if any. These parameters are described by Calabretta and Greisen (called PROJP) in the 1996 draft. In the recent versions, this paper has split into three, and the projection parameters have been reworked into the PV matrix. However, these have not yet been implemented in WCSLIB so we stick with the old ones for now.

Example

    Projection proj(Projection::CAR);
    cerr << proj.parameters() << endl;

This projection requires no parameters so the printed parameter vector would be of zero length.

Thrown Exceptions

AipsError

To Do

Worry about projection parameters which are unit dependent (i.e. radians vs. degrees).
LONGPOLE should probably go in here.

Member Description

enum Type

Hold all the known types of celestial projections.

Projection(Projection::Type which=CAR)

Construct a projection which needs no parameters. SIN is unique in that it can be created with 0 or 2 parameters.

Projection(Projection::Type which, const Vector<Double> &parameters)

Construct a projection which needs parameters. The parameter vector must be the length of the required number of parameters.

Projection(const Projection &other)

Copy constructor (copy semantics).

Projection &operator=(const Projection &other)

Assignment (copy semantics)

~Projection()

Destructor

Projection::Type type() const

What is the Type of this projection?

String name() const
static String name(Projection::Type proj)

What is the type of this projection as a String (e.g. "SIN").

static Projection::Type type(const String &name)

Turn a projection type name into a Type. Used during I/O primarily. Returns N_PROJ if the projection is not known.

static uInt nParameters(Projection::Type proj)
const Vector<Double> &parameters() const

How many parameters does this projection have, and what are they?

Bool near(const Projection &other, Double tol=1.0e-6) const

Comparison to fractional tolerance.

static Bool isZenithal (Projection::Type proj)

Is this projection a 'zenithal' projection