./guide
vshift.pro

Last modification date:

Thu Jun 2 23:56:08 2005

vshift

function vshift(accumnum, [index=integer], [frame=string], [veldef=string], [voffset=double])

Function to calculate the shift, in channels, necessary to align in velocity the primary data container with the data container template in an ongoing accumulation.

You can use an alternate data container by setting index. You can use an alternate global accumulation buffer by setting accumnum.

If the frame is not set, the one implied by the data header is used. Use xshift to align using the current settings of the plotter's x-axis.

Returns

shift, in channels, to be used as argument to shift, returns 0.0 on failure.

Examples

 getps,30
 accum             ; accum first spectrum, no alignment needed yet
 getps,31
 vs = vshift()     ; determine the shift to align scan 31 with scan 30
 gshift,vs         ; apply the shift to scan 31
 accum             ; and add the result to the accumulator
 getps, 32
 gshift, vshift()  ; all in one line, shift 32 to align with 30
 accum
 ave
 

Uses

dcvshift

Version

$Id: vshift.pro,v 1.5 2005/06/02 17:09:44 bgarwood Exp $

Parameters
accumnum in integer (def. 0)	Use this accum buffer. Defaults to the primary buffer, 0. There are 4 buffers total so this value must be between 0 and 3, inclusive.

Keywords
index in, optional integer (def. 0)	The data container that will eventually be shifted. Defaults to the primary data container (0).
frame in, optional string	The reference frame to use. If not supplied, the value implied by the last 4 characters of the velocity_definition in the ongoing accumulation will be used. See frame_velocity for a full list of supported reference frames.
veldef in, optional string	The velocity definition to use. If not supplied, the value implied by the first 4 characters of the velocity_definition in the ongoing accumulation will be used. See frame_velocity for a full list of supported reference frames.
voffset in, optional double	A velocity offset in km/s to apply before aligning. If not set, this defaults to a value of 0.0. A typical use would be to set this equal to the source velocity (at the velocity header value). Not that the units expected here are km/s, in agreement with those expected for setvoffset. The units for the velocity header field are m/s.