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Using Axis Coordinates to Specify Sections   

A further variation is that numerical values in subscript expressions may be specified either as integers, in which case they refer to pixel indices, or as floating-point numbers,[*] in which case they refer to axis coordinates (for a description of axis coordinates, see §[*]). Both linear and non-linear axis coordinates are supported, the values supplied being automatically converted into the corresponding pixel indices before use. For instance:

spectrum(6500.0:7250.0)

could be used to select the appropriate region of a spectrum calibrated in Angstroms, while:

spectrum(5500.0$\sim$21)

would select a 21-pixel wide region of the spectrum centred on 5500.0 Angstroms.



next up previous
Next: Changing Dimensionality
Up: USING SUBSCRIPTS TO ACCESS NDF SECTIONS
Previous: Specifying Centre and Extent


Starlink User Note 33
R.F. Warren-Smith
11th January 2000
E-mail:rfws@star.rl.ac.uk

Copyright © 2000 Council for the Central Laboratory of the Research Councils