New issue 775: Cannot generate isosurfaces of fields that depend on field parameters https://bitbucket.org/yt_analysis/yt/issue/775/cannot-generate-isosurfaces-o... Nathan Goldbaum: Currently in 3.0 isosurfaces that depend on field parameters cannot be generated. As an example: ``` #!python from yt.mods import * pf = load('HiResIsolatedgalaxy/DD0044/DD0044') dd = pf.h.disk('c', [0,0,1], (20, 'kpc'), (3, 'kpc')) radii = (np.arange(100)+1)/100.*20 fluxes = [] for r in radii: iso = pf.h.surface(dd, 'radius', r) print iso['density'] flux = iso.calculate_flux('x-velocity', 'y-velocity', 'z-velocity', 'Density') fluxes.append(flux/1.9891e33*3.15569e13) # solar masses per megayear print r, fluxes[-1] ``` On both unitrefactor and the current 3.0 tip, this fails with the following traceback: ``` #!python Traceback (most recent call last): File "radial_mass_flux.py", line 21, in <module> print iso['density'] File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/data_containers.py", line 205, in __getitem__ self.get_data(f) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/construction_data_containers.py", line 826, in get_data mask, fields, sample_type) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/construction_data_containers.py", line 846, in _extract_isocontours_from_grid vals = grid.get_vertex_centered_data(field, no_ghost = False) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/grid_patch.py", line 293, in get_vertex_centered_data np.add(new_field, cg[field][1: ,1: ,1: ], new_field) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/data_containers.py", line 205, in __getitem__ self.get_data(f) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/construction_data_containers.py", line 491, in get_data if len(gen) > 0: self._generate_fields(gen) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/data_containers.py", line 626, in _generate_fields fd = self._generate_field(field) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/data_containers.py", line 242, in _generate_field tr = self._generate_fluid_field(field) File "/Users/goldbaum/Documents/yt-hg/yt/data_objects/data_containers.py", line 262, in _generate_fluid_field rv = finfo(gen_obj) File "/Users/goldbaum/Documents/yt-hg/yt/fields/derived_field.py", line 181, in __call__ dd = self._function(self, data) File "/Users/goldbaum/Documents/yt-hg/yt/fields/geometric_fields.py", line 49, in _radius return get_radius(data, "") File "/Users/goldbaum/Documents/yt-hg/yt/fields/field_functions.py", line 19, in get_radius center = data.get_field_parameter("center").in_units("cm") AttributeError: 'NoneType' object has no attribute 'in_units' ``` I ran this script in unitrefactor, but the same issue is present in the current 3.0 tip. In this context, 'data' is a covering grid that gets generated by `grid_patch` objects, which have no field parameters. A quick fix might be to somehow pass the field parameters associated with the disk object to the grid patches. When I chatted with Matt a little while ago about this issue, he mentioned that we would need to use the chunking system to generate the covering grid, rather than the old grid-based method. I'm unsure how to do that, so I'm reporting the issue here in hopes of getting some advice or guidance on how to fix this issue.