Q:Hi Any ray_trace experts here?

I am using ray_trace to render images of surface cross sections on top of volume cross sections. I have been following the steps in David’s tutorial (Example 14). This works very fine if the z-axis in world and voxel space are parallel. If this is not the case their seem to be an issue with the texture mapping as the gray levels are not interpolated correct!

Here is what I do:

1. make_slice volume.mnc slice.obj z w 5 2 2
2. plane_polygon_intersect surface.obj lines.obj z 5
3. ray_trace -output image.rgb -nolight -line_width 1 lines.obj -gray 0 300 volume.mnc 0 1 slice.obj -size 1024 1024 -bg white -crop -top -sup 3

ray_trace maps the grey levels of a slice along the z-axis in voxel space - not in world space!

By inspection I have found that the rendered slice exactly corresponds to z=78 (voxel space) wich cuts through z-coordinates 0.9–6.8 in world space.

Am I doing anything wrong?
http://www.bic.mni.mcgill.ca/pipermail/minc-users/2008-May/002036.html

A:I now see that the issue is related to make_slice and not ray_trace!

In the example I provided make_slice creates this:

Q 0.3 0.3 0.4 10 1 2 2 F F
0 1 1 1 1

98.8034 140.093 0.842139
 98.8034 −59.1943 6.75685
 −100.572 140.093 0.842139
 −100.572 −59.1943 6.75685

0 0 1
 0 0 1
 0 0 1
 0 0 1

I had expected a constant z-value of 5