C.8.17.11 Wide Field Ophthalmic Photography Stereographic Projection Module
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#### C.8.17.11 Wide Field Ophthalmic Photography Stereographic Projection Module

Table C.8.17.11-1 specifies the Attributes that describe the Wide Field Photography Stereographic Projection Module.

Table C.8.17.11-1. Wide Field Ophthalmic Photography Stereographic Projection Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Include Table 10-5 “General Anatomy Mandatory Macro Attributes” | The concept code for Anatomic Region Sequence (0008,2218) shall be (T-AA000, SRT, "Eye"), and Defined CID 244 “Laterality” shall be used for Anatomic Region Modifier Sequence (0008,2220). Only a single Item shall be included in Anatomic Region Modifier Sequence (0008,2220).
Transformation Algorithm Sequence | (0022,1513) | 1 | Software algorithm used for stereographic projection. Only a single Item shall be included in this Sequence.
>Include Table 10-19 “Algorithm Identification Macro Attributes” |
Ophthalmic Axial Length | (0022,1019) | 1 | The axial length measurement used for the stereographic projection, in mm.
Ophthalmic Axial Length Method | (0022,1515) | 1 | The method used to obtain the Ophthalmic Axial Length. Enumerated values: MEASURED Measured axial length. ESTIMATED An estimated value based upon performing the examination (i.e. based upon surrogate markers of axial length). POPULATION A length that represents a population norm (i.e. not based upon a measured axial length or surrogate markers of axial length).
X Coordinates Center Pixel View Angle | (0022,1528) | 1 | The horizontal angle covered on the sphere by the center pixel of the projected image, as measured from the center of the sphere, in degrees. See Section C.8.17.11.1.1 for further explanation.
Y Coordinates Center Pixel View Angle | (0022,1529) | 1 | The vertical angle covered on the sphere by the center pixel of the projected image, as measured from the center of the sphere, in degrees. See Section C.8.17.11.1.1 for further explanation.
Ophthalmic FOV | (0022,1517) | 3 | The field of view used to capture the ophthalmic image, in degrees. The field of view is the maximum image size displayed on the image plane, expressed as the angle subtended at the exit pupil of the eye by the maximum dimension 2r (where r equals the radius).

##### C.8.17.11.1 Wide Field Ophthalmic Photography Stereographic Projection Attribute Descriptions

###### C.8.17.11.1.1 Center Pixel View Angle

The Center Pixel View Angle (0022,1528) comprises two real numbers XCENTERPIXELVIEWANGLE and YCENTERPIXELVIEWANGLE that represent in degrees the angle along the horizontal axis and the vertical axis respectively covered by the center pixel in the image, where this angle is measured from the center of the sphere. These are used to convert pixel locations in the image to their corresponding locations on a sphere. x and y are pixel locations (may be sub pixels) in the image, x running from 0 to XPIXELS from the left-hand side of the image to the right-hand side, and y running from 0 to YPIXELS from top to bottom, and if λ denotes the azimuth or longitude on the sphere and ϕ the elevation or latitude on the sphere, both in degrees, then,

where

tan2-1 used to define λ represents the two-argument inverse tangent function:

and

and

The above equations assume the use of degrees throughout. Radians can be used, if XCENTERPIXELVIEWANGLE and YCENTERPIXELVIEWANGLE are given in radians, if all trigonometric functions are switched to their radian-equivalent, and if the factor π/180 is removed from the definition of c.

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