Thank you Roland!

My simulation is running with the Llama multipatch coordinates (Thornburg04). Your suggested method works fine for points inside the cartesian part!

However if I want to choose a point inside the spherical part (outside of the cartesian grid) I can not gather any data.

I assume that the output thorn is only aware of the cartesian coordinates? Do you (or anyone else) know if there is a way to bypass this issue?

My current grid setup is:

Carpet::domain_from_multipatch            = yes
CartGrid3D::type                                      = "multipatch"
CartGrid3D::set_coordinate_ranges_on   = "all maps"
Coordinates::coordinate_system             = "Thornburg04"

Coordinates::h_cartesian                         = 0.1
Coordinates::h_radial                               = 0.11

Coordinates::sphere_inner_radius           = 2
Coordinates::sphere_outer_radius          = 8

Coordinates::n_angular                           = 28

Thanks again and best regards,

Severin Frank