[MINC-users] mincresample -tfm_input_sampling with non-linear transforms

[Andrew Wood]

Hi all,

I'm wondering if someone could explain what mincresample's
-tfm_input_sampling does when it gets a pure non-linear transform. Here's
an example of what I'm trying to understand:

$ mincresample -transform non-linear.xfm input.mnc -tfm_input_sampling
/tmp/output.mnc

# The sampling of the input file:
xspace:step = 0.01 ;
xspace:start = 10.578675 ;
xspace:direction_cosines = 1., 0., 0. ;

yspace:step = 0.1 ;
yspace:start = -6.3 ;
yspace:direction_cosines = 0., 1., 0. ;

zspace:step = 0.01 ;
zspace:start = -6.080117 ;
zspace:direction_cosines = 0., 0., 1. ;

# The sampling of the output file:
xspace:step = 0.0100334812289105 ;
xspace:start = 10.5822486132552 ;
xspace:direction_cosines = 0.999999507537344, 0., 0.000992433912008867 ;

yspace:step = 0.0999999999999996 ;
yspace:start = -6.3 ;
yspace:direction_cosines = 0., 1., 0. ;

zspace:step = 0.0100034724424078 ;
zspace:start = -6.08541455853633 ;
zspace:direction_cosines = 0.00269828695875224, 0., 0.999996359617118 ;

# Note that the transform has an identity linear component:
Transform_Type = Linear;
Linear_Transform =
1  0  0   0
0  1  0   0
0  0  1  0;


Is this sampling change the indented/expected behaviour? Maybe mincresample
is estimating a linear transform from the deformation, and applying it to
the output sampling? Or is this a numerical error somewhere along the way?

Thanks,
Andrew