The way I interpret the help and documentation the vertex with the source are located at negative y for rotation-angle zero. For the x-prime coordinate when converting the arc-geometry for the sensors to linear coordinates it is stated that:
This linear spacing is measured on the x-prime axis. The x-prime axis for each column, COL, of F is oriented at FAN_ROTATION_ANGLES(COL) degrees counterclockwise from the x-axis. The origin of both axes is the center pixel of the image.
As to which sensor is to the right on the sensor-array I think this part of one of the examples in the help:
% Convert angular positions to linear distance along x-prime axis
FposArc = D*tan(FposArcDeg*pi/180);
shows that the positive FposArcDeg is to the right in the detector array.
You could always try with a simpler test-image:
TestImg = zeros(128);
TestImg(32:48,32:48) = 1;
TestImg(78:89,64:85) = 5;
TestImg(20:25,89:100) = 3;
That should make it more straightforward to untangle what is where looking in this or that direction.
HTH
