[yt-users] Error in visualization with new derived field

[Jun-Hwan Choi]

Hi yt-users,

I try to make a density projection of my simulation.
I would like to make a small modification that if the cell density 
higher than a given density ceiling the density value becomes the 
density ceiling.
And, I made a following script:
############################################
from yt.mods import *
import matplotlib.pylab as pylab

def _DensityCeiling(field, data):
     Ceiling = 1e-22
     nx, ny, nz = data["Density"].shape
     DensityCeiling =  na.zeros(data["Density"].shape, dtype='float64')
     DensityCeiling = data["Density"]
     for ix, in range(0,nx):
         for iy, in range(0,ny):
             for iz, in range(0,nz):
                 if(data["DensityCeiling"][ix,iy,iz] > Ceiling):
                     DensityCeiling[ix,iy,iz] = Ceiling
     return DensityCeiling
add_field("DensityCeiling", function=_DensityCeiling, 
units=r"\rm{g}/\rm{cm^3}")


# load up a dataset
pf = load("DD0000/DD0000")
all_center = [0.5, 0.5, 0.5]

pc = PlotCollection(pf,center=all_center)
pc.add_slice("DensityCeiling", 0)
pc.add_slice("DensityCeiling", 2)
pc.add_projection("DensityCeiling", 0)
pc.add_projection("DensityCeiling", 2)

pc.set_width(6, 'kpc')
pc.save("cen_t%04.1f_L6K" % pf.current_time)
pc.set_width(1, 'kpc')
pc.save("cen_t%04.1f_L1K" % pf.current_time)
#######################################################

And then, I got a following error.
File "DenViz.py", line 6, in _DensityCeiling
  nx, ny, nz = data["Density"].shape
ValueError: need more than 1 value to unpack

It turns out that the data["Density"] is not always 3d array but 
sometimes become 1d array.
Is there any way to fix the derived field to avoid this problem?

Thank you in advance,
Junhwan


-- 
--------------------------------------------------------------
Jun-Hwan Choi, Ph.D.
Department of Physics and Astronomy, University of Kentucky
Tel: (859) 897-6737        Fax: (859) 323-2846
Email: jhchoi at pa.uky.edu   URL: http://www.pa.uky.edu/~jhchoi
--------------------------------------------------------------

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