Projection parameters. More...

#include <prj.h>

Data Fields
int	flag

char	code [4]

double	r0

double	pv [PVN]

double	phi0

double	theta0

int	bounds

char	name [40]

int	category

int	pvrange

int	simplezen

int	equiareal

int	conformal

int	global

int	divergent

double	x0

double	y0

struct wcserr *	err

void *	padding

double	w [10]

int	m

int	n

int(*	prjx2s )(PRJX2S_ARGS)

int(*	prjs2x )(PRJS2X_ARGS)

Detailed Description

The prjprm struct contains all information needed to project or deproject native spherical coordinates. It consists of certain members that must be set by the user (given) and others that are set by the WCSLIB routines (returned). Some of the latter are supplied for informational purposes while others are for internal use only.

Field Documentation

int prjprm::flag

(Given and returned) This flag must be set to zero whenever any of the following prjprm struct members are set or changed:

This signals the initialization routine (prjset() or ???set()) to recompute the returned members of the prjprm struct. flag will then be reset to indicate that this has been done.

Note that flag need not be reset when prjprm::bounds is changed.

char prjprm::code

(Given) Three-letter projection code defined by the FITS standard.

double prjprm::r0

(Given) The radius of the generating sphere for the projection, a linear scaling parameter. If this is zero, it will be reset to its default value of $180^\circ/\pi$ (the value for FITS WCS).

double prjprm::pv

(Given) Projection parameters. These correspond to the PVi_ma keywords in FITS, so pv[0] is PVi_0a, pv[1] is PVi_1a, etc., where i denotes the latitude-like axis. Many projections use pv[1] (PVi_1a), some also use pv[2] (PVi_2a) and SZP uses pv[3] (PVi_3a). ZPN is currently the only projection that uses any of the others.

Usage of the pv[] array as it applies to each projection is described in the prologue to each trio of projection routines in prj.c.

double prjprm::phi0

(Given) The native longitude, $\phi_0$ [deg], and ...

double prjprm::theta0

(Given) ... the native latitude, $\theta_0$ [deg], of the reference point, i.e. the point $(x,y)$ = (0,0). If undefined (set to a magic value by prjini()) the initialization routine will set this to a projection-specific default.

int prjprm::bounds

(Given) Controls bounds checking. If bounds&1 then enable strict bounds checking for the spherical-to-Cartesian (s2x) transformation for the AZP, SZP, TAN, SIN, ZPN, and COP projections. If bounds&2 then enable strict bounds checking for the Cartesian-to-spherical transformation (x2s) for the HPX and XPH projections. If bounds&4 then the Cartesian- to-spherical transformations (x2s) will invoke prjbchk() to perform bounds checking on the computed native coordinates, with a tolerance set to suit each projection. bounds is set to 7 by prjini() by default which enables all checks. Zero it to disable all checking.

It is not necessary to reset the prjprm struct (via prjset() or ???set()) when prjprm::bounds is changed.

The remaining members of the prjprm struct are maintained by the setup routines and must not be modified elsewhere:

char prjprm::name

(Returned) Long name of the projection.