`poly_sinogram` and `poly_CT`

Thanks for sharing the preprocessed dataset.
What do `poly_sinogram` and `poly_CT` stand for, please?

```
gt = h5py.File(path, 'r')
Xgt = gt['image'][()]
Spoly = gt['poly_sinogram'][()]
Sgt = np.asarray(ray_trafo(Xgt))
```

Spoly does not seem to be equal to Sgt.


