Brian, This is what matplotlib does. See attached. Best, Unidata IDV Support > Animated gif with numerous, fat contours is clearer > > [cid:76F2C985-9C25-4213-B9FB-DB0E76605743@attlocal.net] > > > On Jan 20, 2016, at 10:37 PM, Brian Mapes > <address@hidden<mailto:address@hidden>> wrote: > > Oh, I notice that smoothing was on in the contour display. When I set the > countours unsmoothed,there is still some purple (color mixing), but it is all > within pixel scale it seems. > > > <PastedGraphic-6.png> > > <IDVcont.colormixing.gif> > > > > > On Jan 20, 2016, at 7:31 PM, Unidata IDV Support > <address@hidden<mailto:address@hidden>> wrote: > > Brian, > > Yes, I don't think it is a problem with the color scale. This may be a subtle > contouring artifact where the contouring algorithm is drifting into areas in > shouldn't, if you see what I mean. This is something you would never notice > except in these two-tone scenarios. (I would continue experimenting with the > contouring parameters rather than the color table at this point.) > > Can you explain to me how you are deriving DTdy? I am curious how other > plotting packages handle these data. > > Best, > > Unidata IDV Support > > I wonder if it is a matter of having only 6 colors in the table? > > No, I made it more (still half red, half blue) using the + in the color table > editor, and changed the range, and the contours are still woozy purplish . > So it is not some color-interpolation thing I think. > > > > On Jan 20, 2016, at 6:44 PM, Unidata IDV Support > <address@hidden<mailto:address@hidden>> wrote: > > Brian, > > Thinking about this a bit more, I don't believe there is a bug or problem > here. > > The color table is being displayed in exactly the manner you wish. In > particular, where you are seeing "blending" are areas where values in the > contour data are actually going back and forth across zero and therefore are > mixed > purple. It is not the colors that are blending, it is the data themselves > across > the "zero boundary". > > Another way of looking at this is choosing a two tone black and white color > table. The white will fade into the background. You will see grey as the data > approach either side of zero. > > Do you buy this theory? :-) > > Best, > > Unidata IDV Support > > Same issue when I import this new table. > Contours are not uniform red or blue, but mixed purple. > Thicker contour line width helps show it. > > [cid:3EC5425C-85EE-4B22-87E4-1F10BC1A1C6C] > > > > > > On Jan 20, 2016, at 3:16 PM, Unidata IDV Support > <address@hidden<mailto:address@hidden><mailto:address@hidden>> wrote: > > Brian, > > It is not that the colors are bleeding, it is your color table that appears to > be discreet, but apparently is not. Remove all other displays and you will see > what I mean. I am unfortunately having trouble loading your bundle though I > did > get it to load once where I was able to come to that conclusion. > > Try the attached color table which I believe is actually discreet. > > Best, > > Unidata IDV Support > > > > See how some of the contours are purplish? The color bar is purely blue/red . > > Is it a bug, or something we have to live with? > Small .zidv bundle attached along with screenshot. > > Brian > > > > > > > > > > Ticket Details > =================== > Ticket ID: WAX-506623 > Department: Support IDV > Priority: Normal > Status: Open > > > = > > > > ********************************************* > Brian Mapes, Professor > Department of Atmospheric Sciences > Meteorology and Physical Oceanography Program > RSMAS, University of Miami > 4600 Rickenbacker Causeway > Miami, FL 33149-1098 > > phone: (305) 421-4275 > fax: (305) 421-4696 > email: address@hidden<mailto:address@hidden> > Web: http://www.rsmas.miami.edu/users/bmapes/ > ********************************************** > > > > > > Ticket Details =================== Ticket ID: WAX-506623 Department: Support IDV Priority: Normal Status: Open
Attachment:
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Attachment:
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MATPLOTLIB COMPARISON
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<2016-01-21 Thu>
Table of Contents
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Brian,
At the end of this analysis, please find meridional temperature gradient
plots.
Let's grab some one degree GFS data from [unidata-server.cloudapp.net].
,----
| import netCDF4
| import numpy as np
| ds =
netCDF4.Dataset('http://unidata-server.cloudapp.net/thredds/dodsC/grib/NCEP/GFS/Global_onedeg/GFS_Global_onedeg_20160121_1200.grib2')
| ds
`----
Examine the `Temperature @ Isobaric surface' variable.
,----
| temp = ds.variables['Temperature_isobaric']
| temp
`----
Take a meridional slice from south to north pole. Also let's sanity
check the data shape.
Our usual imports Python plotting imports.
,----
| %matplotlib inline
|
| import matplotlib.pyplot as plt
| import matplotlib as mpl
`----
Plot up the temperature slice.
,----
| fig = plt.figure(figsize=(10, 5))
| ax = fig.add_subplot(111)
| ax.imshow(tempslice,interpolation='nearest', aspect='auto')
| plt.show()
`----
[file:image/temp.png]
Calculate the temperature derivative in the vertical dimension.
,----
| dTdz = np.gradient(tempslice)[0]
| np.shape(dTdz)
`----
(26, 181)
Define a two-tone color scale.
,----
| # make a color map of fixed colors
| cmap = mpl.colors.ListedColormap(['blue','red'])
| bounds=[-100.0,0.0,100.0]
| norm = mpl.colors.BoundaryNorm(bounds, cmap.N)
`----
Plot `dTdz'.
,----
| fig = plt.figure(figsize=(10, 5))
| ax = fig.add_subplot(111)
| ax.imshow(dTdz,cmap = cmap,interpolation='nearest', aspect='auto')
| plt.gca().invert_yaxis()
| plt.show()
`----
[file:image/temp2.png]
Contours we will plot, but don't plot zero.
,----
| levels = np.ma.masked_inside(np.arange(-10.0,10.0,1.0), -0.01, 0.01)
`----
Plot `dTdz' with contours.
,----
| fig = plt.figure(figsize=(10, 5))
| plt.contour(dTdz,cmap = cmap,levels=levels)
| plt.show()
`----
[file:image/temp4.png]
Overlay contours on top of data.
,----
| fig = plt.figure(figsize=(10, 5))
| ax = fig.add_subplot(111)
| ax.imshow(dTdz,cmap = cmap,interpolation='nearest', aspect='auto', alpha=0.2)
|
| cs = plt.contour(dTdz, cmap = cmap, levels=levels)
| #plt.clabel(cs, cs.levels[::1], inline=True, fontsize=10)
| plt.gca().invert_yaxis()
| plt.show()
`----
[file:image/temp5.png]
[unidata-server.cloudapp.net] http://unidata-server.cloudapp.net