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richard-thomas / MetOffice_NIMROD

Python module to extract data from UK Met Office Rain Radar NIMROD image files
Artistic License 2.0
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MetOffice_NIMROD

Python module to extract data from UK Met Office Rain Radar NIMROD image files.

Features: parses NIMROD format image files, displays header data and allows extraction of raster image to an ESRI ASCII (.asc) format file. A bounding box may be specified to clip the image to the area of interest. Can be imported as a Python module or run directly as a command line script. Originally written in Python 2.7 (see v1.01), but the current version has been converted to run in Python 3.9 without any additional functionality.

(This module is developed from a basic Python script written for a hydrological modelling assignment of my GIS MSc).

Command line usage:

python nimrod.py [-h] [-q] [-x] [-bbox XMIN XMAX YMIN YMAX] [infile] [outfile]
Positional Argument Description
infile (Uncompressed) NIMROD input filename
outfile Output raster filename (*.asc)
Optional Argument Description
-h, --help show this help message and exit
-q, --query Display metadata
-x, --extract Extract raster file in ASC format
-bbox XMIN XMAX YMIN YMAX Bounding box to clip raster data to

Note that any bounding box must be specified in the same units and projection as the input file. The bounding box does not need to be contained by the input raster but must intersect it.

Example command line usage:

python nimrod.py -bbox 279906 285444 283130 290440
    -xq 200802252000_nimrod_ng_radar_rainrate_composite_1km_merged_UK_zip
    plynlimon_catchments_rainfall.asc

Example Python module usage:

import nimrod
a = nimrod.Nimrod(open(
    '200802252000_nimrod_ng_radar_rainrate_composite_1km_merged_UK_zip', 'rb'))
a.query()
a.extract_asc(open('full_raster.asc', 'w'))
a.apply_bbox(279906, 285444, 283130, 290440)
a.query()
a.extract_asc(open('clipped_raster.asc', 'w'))

Notes:

  1. Valid for v1.7 and v2.6-4 of NIMROD file specification
  2. Assumes image origin is top left (i.e. that header[24] = 0)
  3. Tested on UK and European composite 1km and 5km data, using Python 3.9 in Windows 10
  4. Further details of NIMROD data and software at the CEDA Archive website.

Copyright (c) 2021 Richard Thomas

(Nimrod.__init__() method based on read_nimrod.py by Charles Kilburn Aug 2008)

This program is free software: you can redistribute it and/or modify it under the terms of the Artistic License 2.0 as published by the Open Source Initiative .

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.