Converting 3D volume coordinates to 2D screen coordinates is accomplished with the C3DHelpers::Volume2ProjectionPlane(). This method takes a coordinate in 3D volume space and converts it to a 2D screen space coordinate. The C3DHelpers::Volume2ProjectionPlane() method takes into account the current render mode, zoom, slice spacing, camera transform, and view angle settings. The current render mode, zoom, and camera transform can be accessed in the current RENDER_PARAMS structure, which can be obtained with a call to IRenderEngineContext::GetRenderParams() or IRenderQueue::GetRenderParams(). The volume slice spacing can be obtained from the VOLUME_DATA_PARAMS structure. The VOLUME_DATA_PARAMS structure can be obtained with a call to IVolumeDataContext::GetVolumeDataParams(). The view angle parameter can be calculated with a call to the C3DHelpers::GetConvertedViewAngle() method. This method take as input parameters the size of the image being rendered, and the current field of view. These can both be obtained from the current RENDER_PARAMS structure. The C3DHelpers::GetConvertedViewAngle() method returns as an output parameter the converted view angle value to be used with the C3DHelpers::Volume2ProjectionPlane() method.

 

If the input 3D volume coordinate is outside the current view area, the 2D screen space coordinate may be negative, or larger than the window dimensions. Check the 2D screen space coordinates to ensure that the application does not attempt to draw to an off-screen location.

 

RENDER_PARAMS rp;

BCOM_ZEROMEMORY(rp);

 

C3DHelpers c3DHelpers;

 

// Get render params for input parameters.

rp.Mask = (ENUM_RENDER_PARAMS_MASK)(RPM_RENDER_TYPE | RPM_TRANSFORM | RPM_ZOOM | RPM_RENDER_IMAGE_SIZE | RPM_VIEW_ANGLE);

pRenderEngine->GetRenderParams(&rp);

 

// Get converted view angle. This value can be reused as long as the image size and field of view are constant.

h_float64 convertedViewAngle;

c3DHelpers.GetConvertedViewAngle(&convertedViewAngle, &rp.RenderImageSize, rp.ViewAngle);

 

// Get volume data parameters.

VOLUME_DATA_PARAMS volumeData;

BCOM_ZEROMEMORY(volumeData);

pVolumeDataContext->GetVolumeDataParams(&volumeData);

 

// Convert 3D volume coordinates to 2D screen space coordinates.

VECTOR3D projPlanePos;

c3DHelpers.Volume2ProjectionPlane(&projPlanePos, rp.RenderType, 0, 0, 0, rp.Zoom, volumeData.Spacing, &rp.Transform, &rp.RenderImageSize, convertedViewAngle); 

 

Converting 2D screen coordinates to 3D volume coordinates can be accomplished with the C3DHelpers::ShootRayToPointInCenterOfView() or C3DHelpers::ShootRayToPointLocation() methods. These methods take as input parameters the 2D screen space coordinate of a rendered pixel, and the address of an IRenderParamsReciever derived object that rendered the onscreen image (such as an IRenderEngineContext or IRenderQueue object). The C3DHelpers::ShootRayToPointInCenterOfView() and C3DHelpers::ShootRayToPointLocation() methods return as an output parameter the 3D volume coordinates of the first opaque voxel encountered by that ray.

 

The C3DHelpers::ShootRayToPointInCenterOfView() and C3DHelpers::ShootRayToPointLocation() methods make use of the IRenderEngineContext::ShootRayFast() method to shoot a ray of light into the volume. Other ShootRay() methods are available that give more control over how rays are cast into the volume, and return additional data about the voxels they encounter. See the sections on Transfer Functions and The ShootRay() Methods for additional information on these topics.

 

C3DHelpers c3DHelpers;

 

// Shoot ray into volume from center of view window.

VECTOR3D voxelCoordinate;

c3DHelpers.ShootRayToPointInCenterOfView(&voxelCoordinate, pRenderEngine);

 

// Shoot ray into volume from window coordinates 250, 250.

c3DHelpers.ShootRayToPointLocation(&voxelCoordinate, pRenderEngine, 250, 250);

 

The origin for a volume defined in a DICOM series is determined by the position data associated with each slice in the series. The origin for a volume loaded into an HDVR® based application is the center of the volume. This can result in different origins for the DICOM series and the HDVR volume. The C3DHelpers::FoviaRefToDICOM() and C3DHelpers::DICOMRefToFovia() methods can be used to convert between the two coordinate systems. DICOM coordinates can be converted to HDVR coordinates, or vice versa. The C3DHelpers::FoviaRefToDICOM() method takes as input parameters the current RENDER_PARAMS structure, the volume slice spacing, and the origin offset (if any). It returns as an output parameter an hdrcDICOMImageDesc structure that contains the DICOM equivalent coordinate, two vectors describing the relative DICOM series orientation, and the size and spacing of the series. The C3DHelpers::DICOMRefToFovia() method takes an hdrcDICOMImageDesc structure which defines the DICOM coordinate system, as described above. The other fields in the hdrcDICOMImageDesc structure must be filled in as well. The C3DHelpers::DICOMRefToFovia() method also takes the volume slice spacing, and an offset coordinate (if any) to be converted to the HDVR coordinate system. It returns in a RENDER_PARAMS output parameter the converted coordinate in the RENDER_PARAMS::Transform field.

 

 

// Get render parameters.

RENDER_PARAMS rp;

BCOM_ZEROMEMORY(rp);

 

// Get volume data parameters.

VOLUME_DATA_PARAMS volumeData;

BCOM_ZEROMEMORY(volumeData);

pVolumeDataContext->GetVolumeDataParams(&volumeData);

 

// Request transformation for an arbitrary offset.

VECTOR3D volumeOffset;

volumeOffset.x = 100;

volumeOffset.y = 150;

volumeOffset.z = 200;

 

C3DHelpers c3DHelpers;

hdrcDICOMImageDesc dicomImageDesc;

 

// Convert HDVR coordinates to DICOM reference frame.

c3DHelpers.FoviaRefToDICOM(&dicomImageDesc, &rp, volumeData.Spacing, &volumeOffset);

 

// Convert DICOM coordinates to HDVR reference frame.

c3DHelpers.DICOMRefToFovia(&rp, &dicomImageDesc, volumeData.Spacing, &volumeOffset);