[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.

  • Subject: [python #OVJ-523139]: NEXRCOMP plotting with metpy
  • Date: Fri, 12 Nov 2021 12:32:55 -0700
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
===================
NOTE: All email exchanges with Unidata User Support are recorded in the Unidata 
inquiry tracking system and then made publicly available through the web.  If 
you do not want to have your interactions made available in this way, you must 
let us know in each email you send to us.