[MINC-users] ray_trace issue!

[Mishkin Derakhshan]

Hi,

Lasse, did you ever find a workaround for this problem? I too am
having difficulties with the planes not being exactly the same. The
result is that ray_trace only renders about half of the object as the
other half falls just out of plane.

Ex:
make_slice T1.mnc.gz slice.obj z w 55
plane_polygon_intersect lh.pial.obj lh.pial.lines.obj  z 55
set_object_colour lh.pial.lines.obj lh.pial.green.obj green
ray_trace -output ex14.rgb -nolight lh.pial.green.obj -gray 0 200
T1.mnc.gz 0 1 slice.obj -bg white -top

screenshot of output:
http://imgur.com/CK27d.png

Are David MacDonald's instructions #14 still the best approach, and
what other people are using?
http://www.bic.mni.mcgill.ca/users/david/Ray_trace/ray_trace_tutorial.html#Ex14

As a follow up, I am trying to render two objects on the same plane.
Has anyone done this before?

thanks,
mishkin


2008/5/19 Lasse Riis Østergaard <lasse at hst.aau.dk>:
> Hi again
>
> 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. Does make_slice find the closest
> slice in voxel space?
>
> Lasse
>
> Lasse Riis Østergaard wrote:
>> 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?
>>
>> cheers
>> Lasse
>> _______________________________________________
>> MINC-users at bic.mni.mcgill.ca
>> http://www2.bic.mni.mcgill.ca/mailman/listinfo/minc-users
>>
>
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