New vtkVolumeTextureMapper2D class behaviour

[Lisa Sobierajski Avila]

<x-flowed>Hello Jorrit,

I didn't see your attached image....

Let me see if I understand what you are suggesting - if we have a dataset 
that has 10 sample along the Z axis, and a spacing of 1.0, you would like 
the z dimension of that dataset to be 10 units, not 9 as it currently is, 
with the first z plane being 1/2 unit from the z origin. This would not 
match the way we treat vtkImageData (or vtkStructuredPoints) in VTK - since 
we consider that first sample to be at the origin. Of course, with a 
nearest neighbor sampling (which is essentially what you get along the 
major axis with a 2D texture mapping technique) it means the first and last 
planes of data either represent half as much 3D space as the other planes, 
or that the extent of the data goes beyond the bounds of the data. Also, 
this changes based on the interpolation strategy. Maybe the best thing to 
do is to space the planes at the centers of the 10 boxes that are places in 
the 9 units of length - the first one then starting 9/20 of a unit in, with 
each plane separated by 9/10 units. Any other comments?


One other thing to note is that the selection of major direction is not 
implemented correctly yet - I have not figured out what the best strategy 
is for this. Perspective definitely complicated the issue, but even with 
orthographic projections there is the issue of the aspect of the data set, 
where it is in the view box (or view frustum in perspective), how it is 
being cropped and clipped, etc. For most datasets the current simple 
strategy will work, but sometimes you can really see those 2D planes (and 
wish they were going another way!) with thin slab rendering.

Lisa


At 05:45 PM 9/23/99 +0200, Jorrit Schaap wrote:
>Hi,
>
>I have tried the new vtkVolumeTextureMapper2D class, and it works great
>(on an SGI 320 ;-) ). I noticed one thing though: It appears that the
>volume is 'sliced' and rendered with textures, and that the position of
>the planes (slices) has an offset in the z-direction of one spacing
>unit.
>
>In medical imaging it is custom to position the planes at half a spacing
>unit, and give it a thickness of one spacing unit.
>
>I attached an image to clarify my point.
>
>Did anyone else notice this, and has some opinios about this?
>
>Greetings,
>Jorrit Schaap.
>
>
>
>
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