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Fan-beam transform

`F = fanbeam(I,D)`

`F = fanbeam(I,D,Name,Value)`

```
[F,fan_sensor_positions,fan_rotation_angles]
= fanbeam(___)
```

uses name-value pairs to specify the rotation increment and sensor
spacing. Argument names can be abbreviated, and case does not
matter.`F`

= fanbeam(`I`

,`D`

,`Name,Value`

)

`[`

returns the location of fan-beam sensors in
`F`

,`fan_sensor_positions`

,`fan_rotation_angles`

]
= fanbeam(___)`fan_sensor_positions`

and the rotation
angles where the fan-beam projections are calculated in
`fan_rotation_angles`

.

As a guideline, try making `D`

a few pixels larger than
half the image diagonal dimension, calculated as follows.

sqrt(size(I,1)^2 + size(I,2)^2)

The values returned in `F`

are a numerical approximation of
the fan-beam projections. The algorithm depends on the Radon transform,
interpolated to the fan-beam geometry. The results vary depending on the
parameters used. You can expect more accurate results when the image is
larger, `D`

is larger, and for points closer to the middle
of the image, away from the edges.

[1] Kak, A.C., & Slaney, M., *Principles
of Computerized Tomographic Imaging*, IEEE Press, NY,
1988, pp. 92-93.