Convert parallel-beam projections to fan-beam

converts the parallel-beam data `F`

= para2fan(`P`

,`D`

)`P`

to the fan-beam data
`F`

. Each column of `P`

contains the parallel-beam
sensor samples at one rotation angle. `D`

is the distance from the fan-beam
vertex to the center of rotation.

The parallel-beam sensors are assumed to have a one-pixel spacing. The parallel-beam rotation angles are spaced equally to cover [0,180] degrees. The calculated fan-beam rotation angles have the same spacing as the parallel-beam rotation angles, and cover [0,360) degrees. The calculated fan-beam angles are equally spaced with the spacing set to the smallest angle implied by the sensor spacing.

uses name-value pairs to control aspects of the data conversion. Argument names can be
abbreviated, and case does not matter.`F`

= fan2para(`P`

,`D`

,`Name,Value`

)

`[`

returns the fan-beam sensor locations in `F`

,`fan_sensor_positions`

,`fan_rotation_angles`

]
= fan2para(___)`fan_sensor_positions`

and
rotation angles in `fan_rotation_angles`

.