coordsys.torel - Function

Convert absolute coordinate to relative

Synopsis
torel(value, isworld)

Arguments

value	in	Absolute coordinate
		Allowed:	Numeric vector, vector string, vector quantum, record
isworld	in	Is coordinate world or pixel ?
		Allowed:	T, F, unset
		Default:	unset

Returns
Same as input or fail

Description

This function converts an absolute coordinate to a relative coordinate. The coordinate may be a pixel coordinate or a world coordinate.

Relative coordinates are relative to the reference pixel (pixel coordinates) or the reference value (world coordinates) in the sense relative = absolute - reference.

If the coordinate is a pixel coordinate, it is supplied as a numeric vector. If the coordinate is a world coordinate, you may give it in all of the formats described in the formatting discussion.

If the coordinate value is supplied by a Coordsys tool function (e.g. toworld) then the coordinate 'knows' whether it is world or pixel (and absolute or relative). However, you might supply the value from some other source as a numeric vector (which could be world or pixel) in which case you must specify whether it is a world or pixel coordinate via the isworld argument.

Example

- cs := coordsys(direction=T, spectral=T)
-
- aw := cs.toworld([100,100,24], 's')
- rw := cs.torel(aw)
- aw2 := cs.toabs(rw)
-
- aw
23:53:23.781 +01.39.00.821 1.415023e+09 Hz 
- rw
5.943285e+03 arcsec 5.940821e+03 arcsec 2.300000e+04 Hz 
- aw2
23:53:23.781 +01.39.00.821 1.415023e+09 Hz

This example uses world coordinates.

Example

- cs := coordsys(direction=T, spectral=T)
-
- ap := cs.topixel()           # Reference value
- rp := cs.torel(ap)
- ap2 := cs.toabs(rp)
-
- ap
[1 1 1] 
- rp
[0 0 0]
- ap2
[1 1 1]

This example uses pixel coordinates.

Next: coordsys.torelmany - Function Up: coordsys - Tool Previous: coordsys.torecord - Function Contents Index

	Package	general
	Module	images
	Tool	coordsys