[Insight-users] Specifying landmarks in the ThinPlateSplineWarp.cxx example?

[motes motes]

On Sun, Aug 16, 2009 at 5:22 PM, Luis Ibanez <luis.ibanez at kitware.com>wrote:

> Hi Motes,
>
>
>           "Glimpsing at the source leaves no doubt"
>
>
> If you look at lines 120-130 of the ThinPlateSplineWarp.cxx file:
>
>   while (!infile.eof())
>     {
>     infile >>  p1[0] >> p1[1] >> p1[2] >> p2[0] >> p2[1] >> p2[2];
>
>     sourceLandMarkContainer->InsertElement( id, p1 );
>     targetLandMarkContainer->InsertElement( id++, p2 );
>     }
>
> You will see that the first three values of the file are assigned
> to the X,Y,Z coordinates of the first source landmark, while the
> second group of three values is assigned to the X,Y,Z coordinates
> of the first landmark in the group of target landmarks.
>
>
> Note that this is different from how we manage BSplineDeformableTransforms.
>
> In this ThinPlateSpline example there are no deformation vectors.  We use
> a group of landmarks in the Fixed image, that map, one-to-one, to landmarks
> in the moving image.
>
> The triplet ( 180  217  0 )  that you pointed out to in your email,
> correspond
> indeed to the coordinates of a point in the space of the fixed image.
>
> It is the point with coordinates:   X = 180.0, Y = 217.0,  Z = 0.0
>
>
>      Regards,
>
>
>             Luis
>
>




Ok that makes sense, but how would that be used in a registration context
eg. connecting the ThinplateSpline to an optimizer?

The source and target landmarks are choosen manually in the example but I am
working on a project where this is not possible and the registration process
should run automatically.



I am therefore still pretty interested in using the
BSplineDeformationTransform, but I am still stuck with how to create a
non-uniform grid of deformation vectors - if this is even possible with the
current implementation?


Assume that I have defined a 5*5 grid of deformation vectors. Now I want the
deformation vector at location (2,3) to be located at another location, how
would that be possible?


As I understand the only way to create a non-uniform location of deformation
vectors is to change the spacing. But that will only result in non-uniform
spacing arcross dimesions and not within each of the dimesions.

Am I walking down a dark and lonely path trying to make the current
BSplineDeformationTransform more flexible?













>
>
> --------------------------------------------------------------------------------------------
> On Sun, Aug 16, 2009 at 2:10 AM, motes motes <mort.motes at gmail.com> wrote:
>
>> In the ThinPlateSplineWarp.cxx a set of landmarks are read from the file
>> LandmarkWarping3Landmarks1.txt which contains this:
>>
>>   0   0   0        0   0      0
>> 180   0   0      180   0      0
>> 180 217   0      180 217      0
>>   0 217   0        0 217      0
>>   0   0 180        0   0    180
>> 180   0 180      180   0    180
>> 180 217 180      180 217    180
>>   0 217 180        0 217    180
>>  90 108  90       90 130     90
>>
>>
>>
>> As I understand these are 18 landmark points which is actually just
>> deformation vectors. So the 3 first values in the third row:
>>
>> 180  217  0
>>
>> corresponds to a vector at some location pointing 180 unit in the
>> x-direction and 217 units in the y-direction.
>>
>> But where in the image is this vector located?
>>
>> Or are the above landmarks just 'regular' points that are interpolated by
>> the ThinPlateSpline and not deformation vectors?
>>
>>
>>
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