Hi All, I need to set the "center" field parameter for making a projection of the "radial_velocity". I see from the docs how to do that for a data container but its not clear what to do for a projection. The error I am getting at the moment when the "center" is not set is: File "/homeappl/home/regan/appl_taito/YT/Dev-3.0/yt/yt/data_objects/data_containers.py", line 249, in __getitem__ self.get_data(f) File "/homeappl/home/regan/appl_taito/YT/Dev-3.0/yt/yt/data_objects/data_containers.py", line 656, in get_data finfo.check_available(self) File "/homeappl/home/regan/appl_taito/YT/Dev-3.0/yt/yt/fields/derived_field.py", line 146, in check_available validator(data) File "/homeappl/home/regan/appl_taito/YT/Dev-3.0/yt/yt/fields/derived_field.py", line 235, in __call__ raise NeedsParameter(doesnt_have) yt.fields.field_exceptions.NeedsParameter: (['center']) Any tips much appreciated! Cheers, John