• should really bring sample metadata through from the image / points used to create the surfaces (basically just inherit the metadata of the input data)

• I think all the metadata added here should be under the Processing. top level key (it's not quite as clear cut as for most recipe modules, as there is a pronounced change in data format, but still probably best).

I've taken a very different tack in #1288 which tries to achieve the same thing, but with much less boilerplate. With any luck, this will form the basis of all the metadata stuff being handled more or less automatically.

superseeded by #1288