[yt-users] Particles in volume rendering

[Stella Offner]

Thanks, Matt and Stephen! The issue here is that I only have a small  
number of stars (< 100), so calculating a particle density would  
probably cause problems.

It might be possible to use what you suggest below if I don't start  
with a blank field filled with zeros (I also will likely plot in log  
space). I will play around with some of these things and let you know  
if I find something useful...
Stella

>
>
> The main is to define a new field that translates particles to  
> density. This
> example picks out star particles; it should be easy to remove this  
> if you like
> by eliminating the 'sel' stuff below.
>
> import yt.lagos.UniversalFields as uf
>
> def _pdensity_pyx(field, data):
>    blank = na.zeros(data.ActiveDimensions, dtype='float32')
>    if data.NumberOfParticles == 0: return blank
>    uf.CICDeposit_3(data["particle_position_x"].astype(na.float64),
>                 data["particle_position_y"].astype(na.float64),
>                 data["particle_position_z"].astype(na.float64),
>                 data["particle_mass"].astype(na.float32),
>                 na.int64(data["particle_mass"].size),
>                 blank, na.array(data.LeftEdge).astype(na.float64),
>                 na.array(data.ActiveDimensions).astype(na.int32),
>                 na.float64(data['dx']))
>    return blank
>
> add_field("particle_density_pyx", function=_pdensity_pyx,
>          validators=[uf.ValidateSpatial(0)],
> convert_function=uf._convertDensity,
>          display_name=r"\mathrm{Particle\ Density})")
>
> Then you can use the field "particle_density_pyx" as you would  
> "Density". The
> one thing to worry about in the case of stars, is there can be cells  
> with no
> stars in them, which creates problems if you're doing the volume  
> rendering in
> log space. Let me know if you have problems!
>