[Elastix] Coordinates of control points in B-spline transform

S. Klein s.klein at erasmusmc.nl
Wed Apr 15 23:09:12 CEST 2015


Hi Ramon, Coert, the ordering of the parameters is indeed as you mention.
Best,
Stefan

On 15-4-2015 22:15, Coert Metz wrote:
Dear Ramón,

The code that computes the grid origin and spacing is (if I am not mistaking) in src/Common/Transforms/itkGridScheduleComputer.hxx of the elastix sources. Also the TransformParameters.*.txt file should list the GridSpacing, GridSize, GridIndex and GridOrigin from which you can deduce this information. All points are equidistant for sure. If I remember correctly the ordering of the parameters is indeed as you mention.

Regards,
Coert Metz

On Wed, Apr 15, 2015 at 7:56 PM, Ramón Casero Cañas <rcasero at gmail.com<mailto:rcasero at gmail.com>> wrote:
Dear all,

I have a couple of questions about B-splines in elastix:

1) What are the coordinates of the control points in a B-spline transform?

After registering an image to itself, the t.TransformParameters are all zero, as expected for no deformation.

But how's the grid determined, e.g. for a cubic spline?

Let's say e.g. that we have a 1D grid with 5 control points, plus 1 extra point before the grid, plus 2 extra points after the grid, in each dimension.

Are the coordinates of the 5 control points determined by placing one at the centre of the first pixel, and another at the centre of the last pixel, and then the other 3 equidistant between those?

2) Are then the extra ones outside the grid, and equidistant too?

3) Is the convention for the TransformParameters [x1 x2 x3...xN y1 y2 ... yN]?


Best regards,

Ramon.

--
Dr. Ramón Casero Cañas

Institute of Biomedical Engineering
Department of Engineering Science, University of Oxford
Old Road Campus Research Building, Headington
Oxford
OX3 7DQ
UK

tlf         +44 (0) 1865 617716<tel:%2B44%20%280%29%201865%20617716>
twitter   @Ramon_Casero
web      http://www.cs.ox.ac.uk/people/Ramon.CaseroCanas/

_______________________________________________
Elastix mailing list
Elastix at bigr.nl<mailto:Elastix at bigr.nl>
http://lists.bigr.nl/cgi-bin/mailman/listinfo/elastix





_______________________________________________
Elastix mailing list
Elastix at bigr.nl<mailto:Elastix at bigr.nl>
http://lists.bigr.nl/cgi-bin/mailman/listinfo/elastix


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bigr.nl/pipermail/elastix/attachments/20150415/933c3bd7/attachment.html>


More information about the Elastix mailing list