Make transform to disc and back modular
I think it's a good idea to make the transform to disc and back in FRM a function handle that can be replaced by the user in case he wants to use a different transform.
We would add a 'transform' property to FRM which contains a function handle to a transform function.
The transform function would then be called inside the FRM as
[theta,obj.data] = obj.transform(obj.Freq,obj.data,'p2d');
obj.domain = 'DISC';
and to go vack from the disc as
[obj.Freq,obj.data] = obj.transform(obj.Freq_normalised,obj.data,'d2p');
obj.domain = 'PLANE'
When a new transform is set, the FRM should test the provided function to guarantee that the transform to go to the disc and back returns the original data.
A warning should be thrown when the transform does not maintain the norm