Hi David,
This doesn't work for me:
appcd:buckle> setaxis fred dim=3 mode=wcs
appcd:buckle> maths exp='ia*cc+(ca+cb)*0' ia=fred out=fred2
Segmentation fault
I'm trying on a small cube, its only 11x11x25, with RA,DEC and velocity
as axis1, axis2 and axis3 respectively.
maths exp='ia*cc' ia=fred out=fred2
does finish without a segmentation fault, but I don't think it gives me
what I'm after.
Regards,
Jane
David Berry wrote:
> Hi Jane,
> You should be able to use KAPPA:MATHS for this. Maths
> allows you to create an NDF using an arbitrary algebraic combination
> of the data, variance or coordinate values from other NDFs. However
> it's a bit out of date in that it has not been updated to use the
> modern WCS system - it still uses the old AXIS system. So the first
> thing you need to do is to create an AXIS structure describing the
> velocity information in the WCS component:
>
> % setaxis fred dim=3 mode=wcs
>
> (assuming your velocity axis is axis 3). Then you run maths:
>
> % maths exp='ia*cc+(ca+cb)*0' ia=fred out=fred2
>
> The EXP parameter gives the algebraic expression to be stored in the
> output NDF. In this expression, the "ia" token represents the data
> value in the NDF associated with parameter "ia" (e.g. fred.sdf in this
> case), and the "c*" tokens represent the coordinate values. The
> alphabetically earliest "c*" token in the expression represents the
> coordinate on the first axis, etc. This is why you need to include
> "ca" and "cb" in the expression, as otherwise "cc" would be the
> alphabetically earliest "c*" token in the expression and so would give
> the coordinate value on the first axis, rather than the required third
> axis. "ca" and "cb" are multiplied by zero in the expression so that
> they do not affect the values stored in the output NDF.
>
> A bit convoluted I know. It would have been simpler for the meaning of
> each "c*" token to be fixed - ca for the first axis, cb for the second
> etc. But it's history now...
>
> David
>
>
>
>
>
>
> On 20 August 2010 14:08, Jane Buckle <[log in to unmask]> wrote:
>> Hi All,
>>
>> The help for kappa collapse with estimator iwc states "Iwc" --
>> Intensity-weighted co-ordinate, being the sum of each value times its
>> co-ordinate, all divided by the integrated value (see the "Integ" option).
>>
>> How does it do this? I would like to create a 3D cube, the same size as my
>> original cube, but whose data values are the intensity multiplied by the
>> velocity coordinate for each velocity channel.
>>
>> So, basically I would like each value times its coordinate, without any
>> summing. This may well be a simple task, but the method is currently
>> escaping me.
>>
>> cheers,
>>
>> Jane
>> --
>> Dr Jane V. Buckle
>> Cavendish Astrophysics Group and Kavli Institute for Cosmology,
>> Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge
>> CB3 0HE
>> Tel: +44 (0)1223 746436
>>
--
Dr Jane V. Buckle
Cavendish Astrophysics Group and Kavli Institute for Cosmology,
Institute of Astronomy, University of Cambridge, Madingley Road,
Cambridge CB3 0HE
Tel: +44 (0)1223 746436
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