[GEMPAK #AHI-786143]: precipitation values for nex2img

> Hi Steve,
> 
> I'm having a question on precipitation values from the generated GIF file by 
> nex2img.  We have three different RADMOD (C/P/M), and from Gempak display, 
> the max(in inches) is sometimes 8 or 4 on each site, although the color 
> levels are always 16.
> 
> If I read a pixel as PaleGreen3 from n1p.gif, how can I determine the number 
> of inches for this particular location?
> 
> I checked nex2gini.tbl and you specified as below:
> N1P       30    3 inches,10,110,0,2;110,210,2,6;210,255,6,12      TICZ99 CHIZ
> 
> Could you explain this a little bit?
> thanks a lot!
> 
> Ying Cao

Ying Cao,

The level 3 data products are 16 bins as you notices, and the nex2img program 
will determine
the data range that those represent when compositing into the image.

The nex2gini.tbl file provides a series of ranges for pixel and data values. 
For the N1P product, the "30" is a product number for identification in 
$GEMTBL/sat/imgtyp.tbl.
The next number "3" is ths number pixel to value sets. The final grouping:
inches,10,110,0,2;110,210,2,6;210,255,6,12 

Provides the units, followed by the "3"  pixel to value sets. Here, it says that
pixel values 10 to 110 represent the data range of 0 to 2 inches. Pixel values
of 110 to 210 give the range 2 to 6 inches, and the pixels 210 to 255 give
the range 6 to 12 inches. 

The purpose of having 3 range sets is to allow greater resolution  (eg 100 pixel
values for the 0 to 2 inch range) at the lowest end. Similarly, the level 3 
radar
products do not provide a linear set of bin/values but instead concentrate the 
number of bins in the area of needed resolution.

For a program plotting a gini from the nex2gini output, the IMCBAR would provide
a color bar refernce of data value to pixel value. The nex2img program was 
designed to
provide just the image. You can reference the implied data value of a pale
green pixel though its gif value and then calculate the value within the
data range in nex2gini.tbl that pixel represents.

Steve Chiswell
Unidata User SUpport


> 
> 


Ticket Details
===================
Ticket ID: AHI-786143
Department: Support GEMPAK
Priority: Normal
Status: Closed