[MINC-development] Grid transforms

[Andrew Janke]

Hi all,

I understand that a while back the precision of grid transforms went
from short to double. This was probably around the -50 -> + 50
wierdness that used to happen within minctracc.  Perhaps there were
also other rationales.

Were there also other changes to libminc/volume_io to support this? I
ask as I'm getting wierdness with xfmconcat when I feed in a zero grid
transform.  ie:

mincresample -xstep 32 -ystep 32 -zstep 32 \
   -xnelements 10 -ynelements 10 -znelements 10 \
   /opt/minc/share/icbm152_model_09c/mni_icbm152_t1_tal_nlin_sym_09c.mnc
/tmp/like.mnc

minclookup -signed -short -lut_string '0 0 0 0;1 0 0 0'  /tmp/like.mnc
/tmp/like_vector.mnc

mincreshape -dimorder vector_dimension,zspace,yspace,xspace \
   /tmp/like_vector.mnc /tmp/zero_grid_0.mnc

echo "MNI Transform File" > /tmp/zero.xfm
echo "Transform_Type = Grid_Transform;" >> /tmp/zero.xfm
echo "Displacement_Volume = zero_grid_0.mnc;" >> /tmp/zero.xfm

xfmconcat /tmp/zero.xfm /tmp/z.xfm

mincstats /tmp/z.xfm

cai-zeep:tmp$ mincstats z_grid_0.mnc
*** mincstats - reported max (-32768) doesn't equal header (32767)
File:              z_grid_0.mnc
Mask file:         (null)
Total voxels:      3000
# voxels:          3000
% of total:        100
Volume (mm3):      98304000
Min:               -32768
Max:               -32768

Note the messed up min and max. This will work however if you make an
unsigned short volume at the minclookup stage.   If I then use this
transform things of course go awry instead of it being a zero xfm.

So, is this defined or unexpected behaviour? If I use a double, I get
a more interesting error instead of a failure.

xfmconcat ident-32.xfm /tmp/d.xfm
Volume has invalid min and max voxel value


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