DICOM PS3.3 2020c - Information Object Definitions

C.11.30 Volume Render Geometry Module (Current)
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### C.11.30 Volume Render Geometry Module

Table C.11.30-1 contains Attributes that describe the geometry of the volume rendered view.

Table C.11.30-1. Volume Render Geometry Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Render Projection | (0070,1602) | 1 | Projection style. Enumerated Values: ORTHOGRAPHIC PERSPECTIVE
Viewpoint Position | (0070,1603) | 1 | Position of the viewpoint in volume space. A point (x,y,z) in the Volumetric Presentation State Reference Coordinate System.
Viewpoint LookAt Point | (0070,1604) | 1 | Point the viewpoint is looking at. A point (x,y,z) in the Volumetric Presentation State Reference Coordinate System.
Viewpoint Up Direction | (0070,1605) | 1 | Vertical orientation of the view. A vector (x,y,z) in the Volumetric Presentation State Reference Coordinate System.
Render Field of View | (0070,1606) | 1 | The field of view specified as a 6-tuple of values (Xleft, Xright, Ytop, Ybottom, Distancenear, Distancefar) in the Viewpoint Coordinate System, in mm. See Section C.11.30.1.
Rendering Method | (0070,120D) | 1 | The rendering method used during the ray casting compositing operation. Enumerated values: Enumerated Values: MAXIMUM_IP A method that projects the interpolated sample with maximum intensity that falls in the path of each ray traced from the viewpoint to the plane of projection. MINIMUM_IP A method that projects the interpolated sample with minimum intensity that falls in the path of each ray traced from the viewpoint to the plane of projection. VOLUME_RENDERED A method where each XY pixel of the rendered view is determined by accumulating the set of non-transparent voxel samples along a ray.
Sampling Step Size | (0070,1607) | 3 | Spacing in mm between samples along each ray in the original volume rendering operation. See Section C.11.30.2.

#### C.11.30.1 Render Field of View

The Render Field of View (0070,1606) defines the region of the volume data that is displayed.

The viewpoint is positioned and oriented within the Volumetric Presentation State Reference Coordinate System (VPS-RCS) by Viewpoint Position (0070,1603), Viewpoint LookAt Point (0070,1604) and Viewpoint Up Direction (0070,1605). This position and orientation establish a Viewpoint Coordinate System (VCS), which is a right-hand coordinate system in which the viewpoint is positioned at (0,0,0) and is looking at a point at (0,0,-z) and the up direction is along the +y axis.

Render Field of View (0070,1606) is specified by the following coordinate values in the Viewpoint Coordinate System:

- Distancenear, Distancefar specify the distances from Viewpoint Position (0070,1603) to the near and far depth clipping planes. Both distances shall be positive, and Distancenear shall be less than Distancefar.

- Xleft, Xright specify the coordinates of the left and right vertical clipping planes at Distancefar. Xleft shall be less than Xright.

- Ytop, Ybottom specify the coordinates for the top and bottom horizontal clipping planes at Distancefar. Xleft shall be less than Xright.

### Note

Positive values of Distancenear and Distancefar place the near and far rectangles of the field of view on the negative Z axis at Z values of -Distancenear and -Distancefar, respectively.

In the case of a Render Projection (0070,1602) value of ORTHOGRAPHIC, Render Field of View (0070,1606) defines a rectangular cuboid with dimensions (Xright minus Xleft) by (Ytop minus Ybottom) by (Distancefar minus Distancenear), in mm, as shown in Figure C.11.30-1:

Figure C.11.30-1. ORTHOGRAPHIC Field of View Geometry

In the case of a Render Projection (0070,1602) value of PERSPECTIVE, Render Field of View (0070,1606) defines a frustum in which the far rectangle is larger than the near rectangle. The extent of the far rectangle is established by the points (Xleft, Ytop) and (Xright, Ybottom) at Distancefar. The extent of the near rectangle is established by the four points where rays originating at the viewpoint position to the corners of the far rectangle intersect the plane that is located at Distancenear from the viewpoint, as shown in Figure C.11.30-2.

Figure C.11.30-2. PERSPECTIVE Field of View Geometry

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DICOM PS3.3 2020c - Information Object Definitions