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# Class FITSWCS.projections.GLSProjection

    java.lang.Object
       |
       +----FITSWCS.Projection
               |
               +----FITSWCS.projections.GLSProjection

public class GLSProjection
extends Projection

This class provides support for the Sanson-Flamsteed (global sinusoid) projection (GLS) used by the FITS "World Coordinate System" (WCS) convention.

The FITSWCS package was translated from the WCSLIB C library. This original library was written in support for coordinate systems used by astronomical data stored in FITS format. For more information on these coordinate systems, refer to the paper by Greisen and Calabretta at:

> ftp://fits.cv.nrao.edu/fits/documents/wcs/wcs.all.ps.Z

Nomenclature

In WCSLIB the "forward" direction is from (lng,lat) celestial coordinates to (x,y) coordinates in the plane of projection. This accords with the notion that spherical projections are a projection of the sphere onto a plane, the "reverse" direction is therefore that of deprojection from plane to sphere.

Unfortunately, this is opposite to what is generally understood to be the forward direction for FITS, namely that of transforming pixel coordinates to world coordinates. However, the ordering of function argument lists should make it clear what is intended.

Accuracy

Closure to a precision of at least 1.0-10 degree of longitude and latitude has been verified for typical projection parameters on the 1 degree grid of native longitude and latitude (to within 5 degrees of any latitude where the projection may diverge). Notwithstanding this, absolutely no claim is made for the accuracy or reliability of these routines. They are supplied as is, with no warranty of fitness for any purpose.

COPYRIGHT NOTICE

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details.

You should have received a copy of the GNU Library General Public License along with this library; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Correspondence concerning WCSLIB may be directed to:

         Internet email: mcalabre@atnf.csiro.au
         Postal address: Dr. Mark Calabretta,
                         Australia Telescope National Facility,
                         P.O. Box 76,
                         Epping, NSW, 2121,
                         AUSTRALIA

Correspondence concerning the Java implementation may be directed to Raymond L. Plante (rplante@ncsa.uiuc.edu).

##

GLSProjection()
  Create an GLSProjection object
GLSProjection(double)
  Create an GLSProjection object
GLSProjection(double, double[])
  Create an GLSProjection object
GLSProjection(double[])
  Create an GLSProjection object

##

fwd(double, double)
  Compute (x,y) coordinates in the plane of projection from native spherical coordinates (phi,theta).
fwd(double[])
  same as fwd(phitheta[0], phitheta[1])
rev(double, double)
  Compute native spherical coordinates (phi,theta) from the (x,y) coordinates in the plane of projection.
rev(double[])
  same as rev(xy[0], xy[1]);
setProjParm(double[])
  set the projection parameters (which are not used);
setR0(double)
  set the sphere radius

##

GLSProjection

      public GLSProjection()

  Create an GLSProjection object

GLSProjection

      public GLSProjection(double r0)

  Create an GLSProjection object
  Parameters:
    r0 - sphere radius

GLSProjection

      public GLSProjection(double r0,
                           double p[])

  Create an GLSProjection object
  Parameters:
    r0 - sphere radius
    p - projection parameters. None are actually used by this projection; this constructor is provided to parallel other subclasses of the Projection class

GLSProjection

      public GLSProjection(double p[])

  Create an GLSProjection object
  Parameters:
    p - projection parameters. None are actually used by this projection; this constructor is provided to parallel other subclasses of the Projection class

##

fwd

      public double[] fwd(double phi,
                          double theta)

  Compute (x,y) coordinates in the plane of projection from native spherical coordinates (phi,theta).
  Returns:
    double[] a two-element array containing x,y
  Overrides:
    fwd in class Projection

fwd

      public double[] fwd(double phitheta[])

  same as fwd(phitheta[0], phitheta[1])
  Overrides:
    fwd in class Projection

rev

      public double[] rev(double x,
                          double y)

  Compute native spherical coordinates (phi,theta) from the (x,y) coordinates in the plane of projection.
  Returns:
    double[] a two-element array containing phi,theta
  Overrides:
    rev in class Projection

rev

      public double[] rev(double xy[])

  same as rev(xy[0], xy[1]);
  Overrides:
    rev in class Projection

setR0

      public void setR0(double r0)

  set the sphere radius
  Overrides:
    setR0 in class Projection

setProjParm

      public void setProjParm(double p[])

  set the projection parameters (which are not used);
  Parameters:
    p - array of projection parameters; if p is null, no update is to be made.
  Overrides:
    setProjParm in class Projection

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