Re: Setting contour levels using a min/max contour level and a spacing

From: Mary Haley <haley_at_nyahnyahspammersnyahnyah>
Date: Thu Sep 16 2010 - 14:07:29 MDT

Hi,

Without knowing what your data values are, I'm not sure what the reason is behind the lack of red in your plot.

You should print out the min/max of your data to make sure the values are what you expect:

  print("min/max data = " + min(data) + "/" + max(data))

When you select contour levels of 0 and 39, with the colors red and green for these two levels, then what this means is:

   values < 0 will be red
   values >= 0 and < 39 will be green

Since you have a third box that is green, then this means anything >= 39 will be green.

Is this what you intended?

You might want to see example "vegland_1.ncl" at http://www.ncl.ucar.edu/Applications/classification.shtml
for a sample of setting a color bar with just two values.

--Mary

On Sep 16, 2010, at 12:51 PM, ziying-li@hdfgroup.org wrote:

> Mary,
>
> I follow your instruction for below case and got corresponding plot as
> attached.
>
> http://www.ncl.ucar.edu/Support/talk_archives/2010/1903.html
>
> I checked the latitude for this file and the location should be right. But
> I'm not sure why '0' can not be plotted.
>
> Do you know the reason behind it?
>
> Code:
> ----------------------------------------------------------------------------
>
> load "$NCARG_ROOT/lib/ncarg/nclex/gsun/gsn_code.ncl"
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>
> begin
> eos_file=addfile("MOD10_L2.A2000065.0040.005.2008235221207.hdf.he2", "r")
> ; Read file.
> ;To read HDF-EOS2 files, .he2 is appended to the argument.
> ;For more information, consult section 4.3.2 of
> http://hdfeos.org/software/ncl.php.
>
> data_byte=eos_file->Snow_Cover_MOD_Swath_Snow
> ; read data field, getting the clues about
> eos_file->Fractional_Snow_Cover_MOD_Swath_Snow
> ; from print(eos_file)
>
> data=byte2flt(data_byte)
> data@_FillValue = 255b
>
> nlon=4060
> nlat=2708
>
> lat=asciiread("lat_MOD10_L2.A2000065.0040.005.2008235221207.output",(/nlon,nlat/),"float")
> lon=asciiread("lon_MOD10_L2.A2000065.0040.005.2008235221207.output",(/nlon,nlat/),"float")
>
> data@lat2d=lat
> data@lon2d=lon
>
> xwks=gsn_open_wks("pdf","MOD10_L2.A2000065.0040.005.2008235221207_Snow_Cover.ncl")
> colors=(/"white","black","red","green"/)
> gsn_define_colormap(xwks,colors)
>
> setvalues NhlGetWorkspaceObjectId() ; make maximum filesize larger
> "wsMaximumSize" : 200000000
> end setvalues
>
> res=True
> res@cnFillOn=True
> res@gsnMaximize=True
> res@gsnPaperOrientation = "portrait"
> res@cnLinesOn=False
> res@cnLineLabelsOn = False
> res@gsnSpreadColors=True
> res@cnFillMode="RasterFill"
> res@cnMissingValFillPattern = 0 ; missing value pattern is set to "SolidFill"
> res@cnMissingValFillColor=0; white color for missing values
>
> res@cnLevelSelectionMode="ManualLevels"
> res@cnMinLevelValF=0
> res@cnMaxLevelValF=39
> res@cnLevelSpacingF=39
>
> res@lbLabelStrings = ispan(0,39,39)
> res@lbLabelPosition = "Center"
> res@lbLabelAlignment = "BoxCenters"
>
> plot=gsn_csm_contour_map_ce(xwks,data,res)
>
> delete(plot) ; cleaning up resources used
> delete(data)
>
> delete(res)
>
> delete(eos_file)
> end<MOD10_L2.A2000065.0040.005.2008235221207Snow_Cover.JPG>_______________________________________________
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Received on Thu Sep 16 14:07:38 2010

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