[vtkusers] vtkFixedPointVolumeRayCastMapper question

[Lisa Avila]

Looking quickly at your code I don't see anything obviously wrong. However, 
I would suggest trying a few things to isolate the problem:

1) Make sure your first component is the one you want mapped to color, and 
the second is the one you want mapped to opacity.

2) Try volProp->ShadeOff(). Perhaps you do not have good gradients in your 
data and that is causing the problem (although you have a high ambient so 
that shouldn't be the problem...)

3) Leave your ImageSampleDistance at 1.0 (the default). Keep in mind that a 
distance of 0.5 means that you cast 4 rays for every pixels on the screen. 
I believe when OpenGL maps this texture to the screen, it will sample it 
for the pixel value, meaning that you are throwing away 3/4 of the 
information you created during ray casting.

4) If all these fail, try using a solid color transfer function (all values 
map to red for example) - do you get what you expect?


Lisa



At 02:15 PM 5/25/2005, Randall Hand wrote:
>I have a long pipeline setup to render a multifield dataset.  one field I 
>want mapped to opacity, and the other one is a vector that I want 
>magnitude mapped to color.
>My pipeline resembles the following:
>
>
>vtkDataSetReader -> vtkArrayCalculator (to calculate magnitude) -> 
>vtkGaussianSplatter -> vtkImageShiftScale = Dataset with ColorField single 
>component scalar
>            +-> vtkGaussianSplatter -> ImageShiftScale = Dataset with 
> OpacityField single component scalar.
>
>I then do a 
>OpacityData->GetPointData()->AddArray(Colordata->GetPointData()->GetArray("colorField")), 
>and pass the result through a vtkMergeFields to combine the 2 fields into 
>a single dual-component field, and make the new field the Active Scalar.
>
>
>I then construct my volume parts:
>     vtkVolumeProperty *volProp = vtkVolumeProperty::New();
>     volProp->IndependentComponentsOff();
>     volProp->SetColor(xf_Color);
>     volProp->SetScalarOpacity(xf_Opacity);
>     volProp->SetInterpolationTypeToLinear();
>     volProp->ShadeOn();
>     volProp->SetAmbient(0.7);
>
>     // Now setup the Ray Caster
>     vtkFixedPointVolumeRayCastMapper *modelMapper = 
> vtkFixedPointVolumeRayCastMapper::New();
>     modelMapper->SetImageSampleDistance(0.5);
>     modelMapper->SetSampleDistance(0.1);
>     modelMapper->SetInput(mergeFilter->GetOutput());
>
>     // Creating Volume
>     vtkVolume *volume = vtkVolume::New();
>     volume->SetMapper(modelMapper);
>     volume->SetProperty(volProp);
>     volume->Update();
>
>When all is said and done, however, I just get a darkish blurry spot 
>(image Attached).  Can anyone see what's wrong, or have I exposed a bug in 
>the FixedPointVolumeRayCastMapper ?  I've been waiting to do this since I 
>figured out that the old VolumeRayCastMapper couldn't handle 
>multi-component data, and i'm anxious to see this work for once :)
>--
>Randall Hand
><http://www.yeraze.com>http://www.yeraze.com
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