[python #OVJ-523139]: NEXRCOMP plotting with metpy

Hello, and thanks for reaching out!

So, if you're using MetPy's `GiniFile` reader, then that is reading in the 
underlying PNG in these files and providing back pixel values 0-255. As best I 
can tell, these *should* match the original GEMPAK data range [1] of 0-105 
(close to your approximation!) So, if you scale these values to 105 and then 
subtract 30, you'll accomplish the conversion that GEMPAK would to provide a 
final dBZ range of (-30, 75). e.g.,

  data_dbz = data_int / 255 * 105 - 30

However, we here might suggest that if your goal is to better characterize the 
reflectivity at each pixel, consider using a product like MRMS [2]. However, if 
the imagery here works out for your use, don't let me get in the way! Hope this 
helps, and don't hesitate to follow up if not.

  [1]: 
https://github.com/Unidata/gempak/blob/master/gempak/tables/unidata/nex2gini.tbl
  [2]: https://www.unidata.ucar.edu/data/fnexrad.html#mrms_products


All the best,

Drew


> I use metpy and python in general to plot the NEXRCOMP Gini imagery
> 
> E.G:
> N0R, 0.5 degree Reflectivity
> <https://www.unidata.ucar.edu/data/images/nexrcomp/n0r1km.gif>, 1km
> 
> - Pattern Action:
> 
> FNEXRAD ^rad/NEXRCOMP/1km/n0r_(........)_(....)
> FILE    -close  data/gempak/images/sat/NEXRCOMP/1km/n0r/n0r_\1_\2
> 
> All the data flow, metpy and plotting work fine.  My question is on the
> nature of these gini images and the raw data.  The data range goes from 0
> to 200, while dBZ values in the NIDS nexrad III  files are in the -30 to 80
> range.  So to convert the gini, I use something like multiply by .55 to
> make the range 0 to 110, then subtract 30 to get -30 to 80.  And this gives
> images that appear pretty close to what I think the dBZ values are.
> 
> BUT, my question: is there a known conversion to go from the gini NEXRCOMP
> back to dBZ like in the raw NEXRAD III (NIDS) files?



Ticket Details
===================
Ticket ID: OVJ-523139
Department: Support Python
Priority: Low
Status: Closed
===================
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