Dear yt user, I try to use Generic UnicGrid Data (256^3 gas density cube + position of particle that is subset of a huge simulation). It is preliminary work, but I still have some questions. 1. In order to set density unit as cgs, I made following script: ...... data = dict(density = (map, "g/cm**3")) #map is 256^3 density data array bbox = np.array([[0., boxsize], [0., boxsize], [0.,boxsize]]) ds = load_uniform_grid(data, data['density'][0].shape, 3.086e24, bbox=bbox, nprocs=4) ..... Then, I got the following error message: Traceback (most recent call last): File "cutout2.py", line 62, in <module> ds = load_uniform_grid(data, data['density'][0].shape, 3.086e24, bbox=bbox, nprocs=4) File "/Users/jhchoi/common/lib/python2.7/site-packages/yt-3.0dev-py2.7-macosx-10.4-x86_64.egg/yt/frontends/stream/data_structures.py", line 461, in load_uniform_grid psize = get_psize(np.array(data[key].shape), nprocs) AttributeError: 'tuple' object has no attribute 'shape' Hence, I modify "data = dict(density = (map, "g/cm**3"))" --> "data = dict(density = map)" and it work. If this is the case, how can I define the density unit and show it when I make Slice/Projection? In addition, I would like to know how I can set the unit in Generic UnicGrid Data in general? The length unit can be provide to script in load_uniform_grid(... 3.086e24 ....) but I do not know how to set other units. 2. When I add particle information as follow: ..... npart = 100000 # number of particles data = dict(density = map, number_of_particles = npart, particle_position_x = posx, particle_position_y = posy, particle_position_z = posz) bbox = np.array([[0., boxsize], [0., boxsize], [0.,boxsize]]) ds = load_uniform_grid(data, data['density'][0].shape, 3.086e24, bbox=bbox, nprocs=4) ... I got the following error message: Traceback (most recent call last): File "cutout.py", line 107, in <module> ds = load_uniform_grid(data, data['density'][0].shape, 3.086e24, bbox=bbox, nprocs=4) File "/Users/jhchoi/common/lib/python2.7/site-packages/yt-3.0dev-py2.7-macosx-10.4-x86_64.egg/yt/frontends/stream/data_structures.py", line 519, in load_uniform_grid assign_particle_data(spf, pdata) File "/Users/jhchoi/common/lib/python2.7/site-packages/yt-3.0dev-py2.7-macosx-10.4-x86_64.egg/yt/frontends/stream/data_structures.py", line 371, in assign_particle_data pdata.pop("number_of_particles") KeyError: 'number_of_particles' So, I change "number_of_particles = npart," --> "number_of_particles = 100000," and it works. How could it happen? 3. Can I do halo finder (hop/fof) using the above particle data? Or, what information do I need to provide to do grouping? In this case, how can I set the units and linking length? 4. Can I make particle distribution to particle data like data['Dark_Matter_position_x']? This process will allow me additional analysis such as profile and obtaining total value. I may ask too many for new tool, but it will help a lot to use yt for general data set. Thank you, Junhwan