Hi all. I'm trying to make a covering grid of the full domain of an enzo (cosmological) simulation, getting the dark matter density and velocity fields. This works fine with the gas: In [1]: cg = pf.h.covering_grid(0, [0,0,0], [256,256,256], fields=["Density", "x-velocity", "y-velocity", "z-velocity"]) But then I try the DM fields: In [2]: cg = pf.h.covering_grid(0, [0,0,0], [256,256,256], fields=["Dark_Matter_Density", "cic_particle_velocity_x", "cic_particle_velocity_y", "cic_particle_velocity_z"]) ... ipython cruft ... /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/data_objects/data_containers.pyc in __init__(self, level, left_edge, dims, fields, pf, num_ghost_zones, use_pbar, **kwargs) 3342 self.domain_width = na.rint((self.pf.domain_right_edge - 3343 self.pf.domain_left_edge)/self.dds).astype('int64') -> 3344 self._refresh_data() 3345 3346 def _get_list_of_grids(self, buffer = 0.0): /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/data_objects/data_containers.pyc in _refresh_data(self) 3359 3360 def _refresh_data(self): -> 3361 AMR3DData._refresh_data(self) 3362 self['dx'] = self.dds[0] * na.ones(self.ActiveDimensions, dtype='float64') 3363 self['dy'] = self.dds[1] * na.ones(self.ActiveDimensions, dtype='float64') /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/data_objects/data_containers.pyc in _refresh_data(self) 307 """ 308 self.clear_data() --> 309 self.get_data() 310 311 def keys(self): /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/data_objects/data_containers.pyc in get_data(self, fields) 3377 try: 3378 #print "Generating", field -> 3379 self._generate_field(field) 3380 continue 3381 except NeedsOriginalGrid, ngt_exception: /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/data_objects/data_containers.pyc in _generate_field(self, field) 3404 # First we check the validator; this might even raise! 3405 self.pf.field_info[field].check_available(self) -> 3406 self[field] = self.pf.field_info[field](self) 3407 else: # Can't find the field, try as it might 3408 raise KeyError(field) /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/data_objects/field_info_container.pyc in __call__(self, data) 314 ii = self.check_available(data) 315 original_fields = data.keys() # Copy --> 316 dd = self._function(self, data) 317 dd *= self._convert_function(data) 318 for field_name in data.keys(): /project/projectdirs/nyx/yt-installs/yt-hopper/src/yt-hg/yt/frontends/enzo/fields.pyc in _cic_particle_field(field, data) 332 particle_field = field.name[4:] 333 top = na.zeros(data.ActiveDimensions, dtype='float32') --> 334 if data.NumberOfParticles == 0: return top 335 particle_field_data = data[particle_field] * data['particle_mass'] 336 amr_utils.CICDeposit_3(data["particle_position_x"].astype(na.float64), AttributeError: 'AMRCoveringGrid' object has no attribute 'NumberOfParticles' Are you not supposed to use a covering grid with these fields or am I creating the covering grid incorrectly? I get reasonable looking plots if I slice/project cic_particle_velocity_x, so I believe it's working otherwise. Best, Casey