3D Graphics & Viz

Volume Rendering(體繪製)有3種的演算法: RayCast: 圖像空間，雖慢但是很準確的繪制方式。 Splatting: 物體空間 ShearWarp: 結合上述2種方法的優點。

vtkStreamingDemandDrivenPipeline

Executive supporting partial updates.

vtkStreamingDemandDrivenPipeline is an executive that supports updating only a portion of the dataset in the pipeline. This is the style of pipeline update that is provided by the old-style VTK 4.x pipeline. Instead of always updating an entire dataset, this executive supports asking for pieces or sub-extents.

範例:

vtkStreamingDemandDrivenPipeline *exec=
vtkStreamingDemandDrivenPipeline::SafeDownCast(elev->GetExecutive());
        exec->SetUpdateNumberOfPieces(exec->GetOutputInformation(0), numProcs);
        exec->SetUpdatePiece(exec->GetOutputInformation(0), myid);

APIs:

int  PropagateUpdateExtent(int outputPort)
int  SetUpdateExtentToWholeExtent(vtkInformation *)
virtual int  ProcessRequest(vtkInformation *request, 
vtkInformationVector **inInfo, vtkInformationVector *outInfo)
virtual int  Update()
virtual int  Update(int port)
virtual int  UpdateWholeExtent()
int  SetMaximumNumberOfPieces(vtkInformation *, int n)
int  GetMaximumNumberOfPieces(vtkInformation *)
int  SetWholeExtent(vtkInformation *, int extent[6])
void  GetWholeExtent(vtkInformation *, int extent[6])
int *GetWholeExtent(vtkInformation *)
int  SetUpdateExtent(vtkInformation *, int extent[6])
void  GetUpdateExtent(vtkInformation *, int extent[6])
int *GetUpdateExtent(vtkInformation *)
int  SetUpdateExtent(vtkInformation *, int piece,
int numPieces, int ghostLevel)
int  SetUpdatePiece(vtkInformation *, int piece)
int  GetUpdatePiece(vtkInformation *)
int  SetUpdateNumberOfPieces(vtkInformation *, int n)
int  GetUpdateNumberOfPieces(vtkInformation *)
int  SetUpdateGhostLevel(vtkInformation *, int n)
int  GetUpdateGhostLevel(vtkInformation *)
int  SetRequestExactExtent(int port, int flag)
int  GetRequestExactExtent(int port)
int  SetExtentTranslator(vtkInformation *,
vtkExtentTranslator *translator)
vtkExtentTranslator *GetExtentTranslator(vtkInformation *info)
int  SetWholeBoundingBox(int port, double bb[6])
void  GetWholeBoundingBox(int port, double bb[6])
double *GetWholeBoundingBox(int port)

vtkElevationFilter

generate scalars along a specified direction.

vtkElevationFilter is a filter to generate scalar values from a dataset. The scalar values lie within a user specified range, and are generated by computing a projection of each dataset point onto a line. The line can be oriented arbitrarily. A typical example is to generate scalars based on elevation or height above a plane.

vtkElevationFilter範例:

vtkElevationFilter *elev = vtkElevationFilter::New();
        elev->SetInput( shrink->GetOutput() );
        elev->SetLowPoint(-1,-1,-1);
        elev->SetHighPoint( 1, 1, 1);
        elev->SetScalarRange(0,1);

或是在ParallelIso之中的例子

vtkElevationFilter *elev=vtkElevationFilter::New();
        elev->SetInput(iso->GetOutput());
        val = (myid+1) / static_cast(numProcs);
        elev->SetScalarRange(val, val+0.001);

APIs:

• SetLowPoint: Define one end of the line (small scalar values).
• SetHighPoint: Define other end of the line (large scalar values).
• SetScalarRange: Specify range to map scalars into.

vtkMarchingCube是繪製出Isosurface的方法。

Human Femur

I built a femur by this pipeline: vtkVolume16Reader->vtkImageGaussianSmooth->vtkMarchingCubes-> vtkDecimate->vtkSTLWriter Once I build the isosurface, then I use vtkCutter to generate several spaced contours, then save this contours to a DXF file. now this dxf file contains sever layer contours, but i am not famillar with CAD programs, if it is possible to generate a solid model based on these contour layers?

Daniel所寫

平行程式會面對的課題: I mean the ray cast functions, composite and MIP, as well as the existing isosurface implementation.

要使用vtk作到平行化的應用程式，需要用到vtkMultiProcessController, vtkMPIController。

Parallel Pipeline:

1. Initialize():
2. The use of user-defined communicators are supported with vtkMPICommunicator and vtkMPIGroup.
3. SetSingleMethod()
4. SingleMethodExecute()
5. Finalize():

作者為Geveci, Berk

API@vtkMPIController列表:

virtual void  Initialize(int *argc, char ***argv)
virtual void  Finalize()
virtual void  SingleMethodExecute()
virtual void  MultipleMethodExecute()
void Barrier()
virtual void  CreateOutputWindow()
void  SetCommunicator(vtkMPICommunicator *comm)
int  NoBlockSend(int *data, int length, int remoteProcessId,
 int tag, vtkMPICommunicator::Request &req)

Hi, 
        I am doing some research on medical visualization and real time volume  
rendering. About display the reconstruction result, there are  many system and algorithm 
.  
        About reconstruction, I think the segmentation is key problem. Many company  
or reseacrh unit use human expert to complish this task. In this area, some image 
processing technique can be used but interaction by people is hardly avoid. 
        About rendering the reconstruction result or segmentation result, it is 
a hot point in computer graphics. (that is what I do now). Two famous software 
(free) is VTK and VolVis. These two system can be extend by yourself. I think it can 
be satisfy your demand for display.  
        The problem for display 3D model od resconstrction is the data is too large 
, so that it must be handled for several minutes and occupy a lot of memory. Extract 
isosurface or disply volume data directlyare two methods fro display it. Both are slow 
but the former is faster than later. 
        For visualization, the IEEE Visualization proceeding is a good collection 
. Many new technique can be found in it. The 90, 91,92,93,94 can be found in tsinghua 
library in microphoto format. Another publish collection is Visualization on 
Biomedical computing proceeding and SPIE medical imaging series.  
        I expect we can discuss and study together or same interests by email. 
        BTW, there are Vis FAQ in Ohio university web site. I will post the address 
here ASAP. 

使用Vtk函式庫的Pipelines，簡略整理成如下的流程，簡稱為DPM-AV-RIW:

1. 讀入Datasets: 使用vtkImageReader, vtkDICOMImageReader...各類不同的Reader，將資料讀入，然後讀轉出成Geometry資訊。
2. 設定屬性(Property): 使用vtkVolumeProperty作出VolProperty物件，再使用vtkPiecewiseFunction, vtkColorTransferFunction設定VolProperty的不透明度、顏色...的屬性，然後藉由SetScalarOpacity(Piecewise), SetColor(Color), SetInterpolationTypeToLinear(), ShadeOn()，來設定VolProperty的屬性。
3. 設定幾何資訊(Mapper): 利用vtkVolumeRayCastMapper, vtkFixedPointVolumeRayCastMapper作出VolMapper物件。
4. Actor2D, Actor, vtkVolume
5. vtkRenderer
6. RenderWindow
7. RenderWindowInteractor, InteractorStyle

所有的Member Functions列表:

void    PrintSelf(ostream &os, vtkIndent indent)
void    SetDirectoryName(const char *dn)
double *GetPixelSpacing()
int     GetWidth()
int     GetHeight()
float *GetImagePositionPatient()
int     GetBitsAllocated()
int     GetPixelRepresentation()
int     GetNumberOfComponents()
const char *GetTransferSyntaxUID()
float   GetRescaleSlope()
float   GetRescaleOffset()
const char *GetPatientName()
const char *GetStudyUID()
const char *GetStudyID()
float   GetGantryAngle()
virtual int CanReadFile(const char *fname)
void    SetFileName(const char *fn)
virtual char *GetDirectoryName()