20020708: nex2gini specifics

Pete,

There are 16 values in a nids N0R product. Some of the values
in clear air and precip mode are duplicates. Basically,
in clear air, the range is -28 to 28 dbz, and in precip
mode is 0 to 75 dbz. Each of those values isa possible
value in the Gini image. The interpretation below
is correct in that it tells the plotting program to
map brightness values of 0 to 105 to -30 to 75 dbz.
However, since a NIDS product is only discrete values of data ranges, 
there are only a small number of unique values you can possibly get for N0R.

GEMPAK takes the colors in the color table, and assigns the ratio of the
numbert of colors to the data range to evenly distribute the colors over
the data range. Eg, if you have 2 colors in the color table, you
would get the first color representing from -30 to 22 dbz and the
second from 22 to 75 dbz (roughly). If you used 105 colors, you
would have a 1 to 1 mapping of colors to possible dbz values....
but only about 24 colors would ever be in the GINI image.

Steve Chiswell


>From: address@hidden (Pete Pokrandt)
>Organization: UCAR/Unidata
>Keywords: 200207082019.g68KJua08129

>
>Steve,
>
>I'm utilizing the NIDS GINI composites that you produce and send out
>and also am playing around with creating my own local composites.
>
>One of our grad students was wondering what levels of dbz are in
>the 1km national N0R composities you create (or more generically, 
>in any composites created from N0R data via nex2gini). I've been 
>banging my head around trying to figure it out and just getting 
>more and more confused.
>
>I did see this in the tables/unidata/nex2gini.tbl:
>
>N0R       27    1 dBZ,0,105,-30,75           TICZ99 CHIZ
>
>Am I correct in assuming that this means that brightness values
>0 - 105 in the GINI file correspond to dbz values from -30 to 75 dbz?
>That is, there's 1 dbz resolution in the GINI brightness values
>and they go from -30 to +75?
>
>If not, can you help me understand what is actually stored in the
>GINI File?
>
>I also am confused at how the color values in upc_ref24.tbl get
>mapped to dbz or brightness values.  How do the 24 colors get
>mapped to the 105 or so brightness values?  Would it be possible
>to plot with 1 dbz resolution (not that I want to but..) with
>different colors for each dbz value by using a different
>LUT file?
>
>Sorry to sound so scatterbrained, but first day back from vacation
>and digging around in the gempak source code has me pretty fried!
>
>Thanks,
>
>Pete
>
>--
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