[daip] aips_gripe

[Leonia Kogan]

Lincoln,

The difference can be explained by the mistake in the parameter of 
ALTDEF which should be used to add or alter the description in the
catalogue map header of the relationship between the spectral-line velocity 
and the frequency.

Please check that for the both cubes. Pay special attention on
RESTFREQ. I think the AXREF should be the same  for frequency and velocity 
axes?

I'll look in the fortarn later.

regards

Leonia
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>From owner-daip at kochab.cv.nrao.edu Thu Nov 16 07:08 MST 2000
Date: Thu, 16 Nov 2000 09:04:55 -0500 (EST)
From: Lincoln Greenhill <lincoln at rgalp7.harvard.edu>
Subject: [daip] aips_gripe
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{16-NOV-2000 08:59:52}
{rgalp7       UN-REGISTERED!!!!!!!}
{   24  31DEC99  DEC}
{lincoln greenhill}
{cfa, cambridge}
{617 495 7194}
{ALTSW does not seem to correctly compute channel spacings in velocity.
 In my example I have two cubes the correspond to two IFs, each with a
 different sky frequency at the reference pixel.  The channel spacing in
 velocity computed for each cube is different despite my specification of
 the radio definition of Doppler shift.
  
 In my example, restfreq=22235.080 MHz, channel spacing=31.25 kHz,
 veltype=radio, veldef=sun, for cube 1, reference pixel frequency=22185.35 MHz.
 The channel spacing in velocity should be 0.4213394 km/s, assuming the
 radio definition of Doppler shift.  Instead, ALTSW computes 0.42136566 km/s.
 In the second cube, the reference pixel is 22198.70 MHz.  The respective
 channel spacing in velocity is 0.42111227 km/s.
  
  }
{ALTSW seems to compute channel spacing in velocity incorrectly.}
{greenhill at cfa.harvard.edu}
{ }


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