[Matplotlib-users] How to contour plot my water quality data?

Hello, I hope someone can give me a tip to get this working.

I have some data that I have manipulated in to the following format:

x_dim is a 1D array of sample times (in minutes)
array([   0,   30,   60,   90,  120,  150,  180,  210,  240,  270,  300,
        330,  360,  390,  420,  450,  480,  510,  540,  570,  600,  630,
        660,  690,  720,  750,  780,  810,  840,  870,  900,  930,  960,
        990, 1020, 1050, 1080, 1110, 1140, 1170, 1200, 1230, 1260, 1290,
       1320, 1350, 1380, 1410])
x_dim is often, but not always regularly spaced and will in practice be much
much larger.

y_dim is a 1D array of sample depths
array([   0.,  -10.,  -20.,  -30.,  -40.,  -50.,  -60.,  -70.,  -80.,
        -90., -100., -110., -120., -130., -140., -150., -160., -170.,
       -180., -190., -200., -210.])
y_dim is always regularly spaced and won't get much bigger than this

z_dim is a dictionary of  2D arrays of data values where:
z_dim['salin'][1,:] is an array of salinity data taken at the second
sampling (time 30) with one value for every depth in y_dim:
z_dim['salin'][1,:]  =
array([         NaN,  10.14000034,  10.14333344,  10.1766669 ,
        10.22333336,  10.26000023,          NaN,  10.21000004,
        10.21000004,  10.19999981,  10.15999985,  10.12800007,
        10.10333347,  10.09666697,  10.07000001,  10.06333351,
        10.05000019,  10.03666655,  10.01666705,   9.99333318,
         9.97999954,          NaN])
I put in the numpy.nan where I have no data.

I tried to run this through griddata to make sure the times are regular with
something like this:

import matplotlib, numpy
xi = arange(0,x_dim[-1] + 30,30)
zi = mlab.griddata(x_dim,y_dim,z_dim['salin'],xi,y_dim)
# but it complains that "inputs x,y,z must all be 1D arrays of the same
length"
# I can't find any example of griddata that use arrays rather than functions
for z.

# in my exampley_dim IS regular, so I should be able to skip on to plotting.

x_grid,y_grid = meshgrid(x_dim,y_dim)
z_grid = transpose(z_dim['salin'])
# x_grid, y_grid, and z_grid now have the same shape
# Now mask out all the NaNs
ma.fix_invalid(z_grid)
# I have previously figured out level_min and level_max for this dataset.
contour_levels = list(linspace(floor(level_min),ceil(level_max),10))
figure = pyplot.figure()
contour_plot = pyplot.contourf(x_grid,y_grid,z_grid,contour_levels)
cbar = pyplot.colorbar()
pyplot.show()
#and that doesn't look right at all.

Any tips are greatly appreciated.