Hi,
The reason for this is that mni2tal is trying to be tolerant of you
entering coordinates as a (xyz by number of coordinates) matrix, or a
(number of coordinates by xyz) matrix. By default it's expecting the
latter, but if you send it an N by 3 matrix, it assumes you meant the
former. When N is 3 it's ambiguous of course, and in that case
assumes you mean its default,
Best,
Matthew
On 1/24/07, Will McGeown <[log in to unmask]> wrote:
> Hi hopefully someone out there can help because I'm pretty confused.
>
> I am using mni2tal and I'm encountering a potential problem.
>
> Whenever I input for example 1 set of co-ordinates (xyz) the conversion
> takes place and there are no problems. When I try two sets of co-
> ordinates again no problems. If I input three sets of co-ordinates the
> conversion changes (and appears to be wrong). If I try four sets (or
> more) the conversion appears to be correct again.
>
> Why should the program fail when attempting three sets of co-ordinates but
> be ok when inputing other numbers of sets?
>
> I have included an example below: I start off by doing three sets
> individually to demonstrate the transformation. Then I try two sets,
> three sets (where the problem appears to be - see the altered co-
> ordinates), four sets (where they return to normal), five sets and six
> sets. The problem with the conversion seems to take place only when
> inputting three sets. But why should this be? I wonder if everyone that
> uses the utility are aware of this?
> Is there another way of defining the matrix that gets around this problem?
>
> >> mni2tal( [30 30 -
> 4] )
>
> ans =
>
> 29.7000 28.8957 -4.8102
>
> >> mni2tal( [-12 52 -12] )
>
> ans =
>
> -11.8800 49.8732 -12.5884
>
> >> mni2tal( [-40 18 26] )
>
> ans =
>
> -39.6000 18.6337 23.0175
>
> >> mni2tal( [30 30 -4; -12 52 -
> 12] )
>
> ans =
>
> 29.7000 28.8957 -4.8102
> -11.8800 49.8732 -12.5884
>
> >> mni2tal( [30 30 -4; -12 52 -12; -40 18
> 26] )
>
> ans =
>
> 29.7000 29.7000 -3.9600
> -13.3048 51.2046 -10.4300
> -32.9763 14.0184 24.4719
>
> >> mni2tal( [30 30 -4; -12 52 -12; -40 18 26; -42 14
> 40] )
>
> ans =
>
> 29.7000 28.8957 -4.8102
> -11.8800 49.8732 -12.5884
> -39.6000 18.6337 23.0175
> -41.5800 15.4023 36.0753
>
> >> mni2tal( [30 30 -4; -12 52 -12; -40 18 26; -42 14 40; -22 22
> 28] )
>
> ans =
>
> 29.7000 28.8957 -4.8102
> -11.8800 49.8732 -12.5884
> -39.6000 18.6337 23.0175
> -41.5800 15.4023 36.0753
> -21.7800 22.6008 24.6613
>
> >> mni2tal( [30 30 -4; -12 52 -12; -40 18 26; -42 14 40; -22 22 28; -10 26
> 38] )
>
> ans =
>
> 29.7000 28.8957 -4.8102
> -11.8800 49.8732 -12.5884
> -39.6000 18.6337 23.0175
> -41.5800 15.4023 36.0753
> -21.7800 22.6008 24.6613
> -9.9000 26.9358 33.6558
>
>
> Cheers
>
> Will
>
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