[MINC-users] dcm2mnc and (ir)regular spacing?

[Alex Zijdenbos]

On Sun, Jan 8, 2012 at 11:09 AM, Andrew Janke <a.janke at gmail.com> wrote:
> Hi Alex,
>
> On 7 January 2012 00:17, Alex Zijdenbos <zijdenbos at gmail.com> wrote:
>> I am a bit puzzled by this MINC header:
>>
>> minc.hdr (http://cl.ly/1D0x0a3x002Y0w2O242U)
>>
>> specifically w/respect to the spacing along the time dimension. Towards the bottom of the header there is info for the time dimension; however, the time:spacing attribute is "regular". Shouldn't the time:spacing attribute be "irregular", given that the spacing is in fact not regular?
>
> My read of your header has time at a pretty constant 4s?

For the most part yes; but there is at least one discontinuity in it,
with a step of >86000s, no?

> Steps also
> can be ever so slightly different, currently defined here as 0.005:
>
>   https://github.com/andrewjanke/minc/blob/master/conversion/dcm2mnc/dicom_to_minc.h#L106
>
> And a dimension will still be called regular. The logic for this is here:
>
>   https://github.com/andrewjanke/minc/blob/master/conversion/dcm2mnc/minc_file.c#L182

That all makes sense I guess; however, shouldn't there conceptually be
agreement between the presence of the (ir)regular <dim>:spacing
attribute value, and the presence of a (likely irregular) list of
positions in the data section? In other words, if the spacing is
judged to be regular, why would there still be an explicit list of
positions in the header (the underlying question being, what do/should
applications use)?

Thanks,

-- A