On Thu, 26 Mar 2009, David Nutter wrote:
> Thanks for the response. The command works in the direction that I can
> already do, but doesn't give the right answer in the reverse direction
>
> asttrann this=a20080301_00042_01_0001 forward=t posin='"1993,1,2008.2"'
> 10.1966515399 1 0.34544201875006
>
> index 1993 corresponds to 10.19 kms-1, but if I try the reverse (the
> one I am looking for)
>
> asttrann this=a20080301_00042_01_0001 forward=t posin='"10.19665,1,2008.2"'
> 120.34833752056 1 0.34544201875006
>
> I don't get back the 1993 index (it is presumably doing the same
> transformation again), Changing the forward flag to false causes an
> error which looks like the error that wcstran was fond of giving
>
> asttrann this=a20080301_00042_01_0001 forward=f posin='"10.19665,1,2008.2"'
> !! AST: Error in routine AST_TRANN.
> ! astTranN(FrameSet): An inverse coordinate transformation is not defined by
> ! the FrameSet supplied.
> ! Error transforming a set of N-dimensional positions.
> ! Application exit status AST__TRNND, coordinate transformation not defined
> ! this=a20080301_00042_01_0001 forward=f posin="10.19665,1,2008.2"
>
> Is there any way to persuade the routine to work in reverse?
Good (paradoxically), that make's more sense than what I saw (what you see
depends on which cube you pick).
As Tim and David point out the real answer is to use make sure the cube
has an inverse transformation by running the SMURF TIMESORT command, then
either ASTTRANN or WCSTRAN will work and dates like "2007-05-26T13:40:43"
can be used as well as decimal years.
Cheers,
Peter.
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