[IGSTK-Users] CTImageReader voxel origin

[Christopher Heath]

Hello,

I am trying to integrate another application (in IDL) with IGSTK.  The  
purpose of the IDL code is to locate the centers of fiducial markers  
from a CT image.  The code outputs the x, y, and z coordinates of the  
markers.  I would like to use these values with  
igstkLandmark3DRegistration to register tracker space to CT space.   
However, the coordinates I receive from my IDL code are offset by an  
obscure amount from their corresponding values as reported by IGSTK.   
(I find the IGSTK-reported coordinates using the "picker" code from  
NeedleBiopsy). My CTImageSpatialObject's parent is m_WorldReference  
with the Identity transform relationship between them.

In this setup, how can I determine where the origin of the CT image  
is?  Is there anyway to easily transform the CTImage so that all  
coordinates are positive and the origin (0,0,0) is located in the  
corner of the first slice?  I cannot simply find the translation  
between the two and apply it because the values I get from IGSTK are  
not as precise as the ones I get from IDL.  Also, the relationship  
changes for different CT Images.

Thanks,
Chris


Christopher Heath
Vanderbilt University School of Engineering
christopher.c.heath at vanderbilt.edu