log.h File Reference

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Functions
int	logx2s (double crval, int nx, int sx, int slogc, const double x[], double logc[], int stat[])
	Transform to logarithmic coordinates.
int	logs2x (double crval, int nlogc, int slogc, int sx, const double logc[], double x[], int stat[])
	Transform logarithmic coordinates.
Variables
const char *	log_errmsg []
	Status return messages.

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Detailed Description

These routines implement the part of the FITS WCS standard that deals with logarithmic coordinates. They define methods to be used for computing logarithmic world coordinates from intermediate world coordinates (a linear transformation of image pixel coordinates), and vice versa.

logx2s() and logs2x() implement the WCS logarithmic coordinate transformations.

Argument checking:
The input log-coordinate values are only checked for values that would result in floating point exceptions and the same is true for the log-coordinate reference value.

Accuracy:
No warranty is given for the accuracy of these routines (refer to the copyright notice); intending users must satisfy for themselves their adequacy for the intended purpose. However, closure effectively to within double precision rounding error was demonstrated by test routine tlog.c which accompanies this software.

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Function Documentation

int logx2s	(	double	crval,
		int	nx,
		int	sx,
		int	slogc,
		const double	x[],
		double	logc[],
		int	stat[]
	)

logx2s() transforms intermediate world coordinates to logarithmic coordinates.

Parameters:

[in,out]	crval	Log-coordinate reference value (CRVALia).
[in]	nx	Vector length.
[in]	sx	Vector stride.
[in]	slogc	Vector stride.
[in]	x	Intermediate world coordinates, in SI units.
[out]	logc	Logarithmic coordinates, in SI units.
[out]	stat	Status return value status for each vector element: 0: Success. 1: Invalid value of x.

Returns:

Status return value:

• 0: Success.
• 2: Invalid log-coordinate reference value.
• 3: One or more of the x coordinates were invalid, as indicated by the stat vector.

int logs2x	(	double	crval,
		int	nlogc,
		int	slogc,
		int	sx,
		const double	logc[],
		double	x[],
		int	stat[]
	)

logs2x() transforms logarithmic world coordinates to intermediate world coordinates.

Parameters:

[in,out]	crval	Log-coordinate reference value (CRVALia).
[in]	nlogc	Vector length.
[in]	slogc	Vector stride.
[in]	sx	Vector stride.
[in]	logc	Logarithmic coordinates, in SI units.
[out]	x	Intermediate world coordinates, in SI units.
[out]	stat	Status return value status for each vector element: 0: Success. 1: Invalid value of logc.

Returns:

Status return value:

• 0: Success.
• 2: Invalid log-coordinate reference value.

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Variable Documentation

const char * log_errmsg[]

Error messages to match the status value returned from each function.

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