[netcdf-java] Reading grib2 with LambertConformal_Projection -> lat / lng

• To: netcdf-java@xxxxxxxxxxxxxxxx
• Subject: [netcdf-java] Reading grib2 with LambertConformal_Projection -> lat / lng
• From: Harold <harold@xxxxxxxxxxxxxx>
• Date: Tue, 18 Jun 2019 10:37:31 -0600

Hello,

First, thanks for this lib; it is very helpful and I don't know where we'd
be without it.

I encountered my first netcdf (.grib2) files recently, and hope to access
the data therein to verify the output of another system.

Here's an example file, if that helps:
 - https://s3.us-east-2.amazonaws.com/tech.public.data/grib2-test/3600.grib2

I found PanoplyJ, which works great, and summarizes the file like this:
 - https://i.imgur.com/VJXnpWH.png

I am using the java libs `edu.ucar/cdm` and `edu.ucar/grib`, both at
version 4.6.13 - which also work great and open the file without trouble.

My intention is to verify the contents of this file against a different
dataset which expresses surface location with lat/lng, while this grib2
file has x/y (under a Lambert conformal mapping).

The path I found through the lib yesterday is:
1) NetcdfDataset/openDataset
2) .getVariables and store a reference to the `LambertConformal_Projection`
variable
3) Construct a `LambertConformalConic` and call `.makeCoordinateTransform`
with the dataset and the variable
4) From that I can `.getProjection`
5) Then I make a `float[][]` out of the separate x/y variables
6) Then I can call `.projToLatLon` with the projection and the `float[][]`
7) After this I go linear over the contents of the `Temperature_surface`
variable associating each one with the correct lat/lng.

This actually works, but I am wondering if there is a better way.

I have a feeling that there is some higher level API that I missed that
would do all this more automatically, and possibly more generally. My code
feels brittle and over-specific to this particular file.

Or, put another way, how best to (given a lat/lng) query the temp at that
location in this file?

With warm appreciation for your time,
-Harold

• Follow-Ups:
  • Re: [netcdf-java] Reading grib2 with LambertConformal_Projection -> lat / lng
    • From: Schmunk, Robert B. (GISS-611.0)[SciSpace LLC]
  • Re: [netcdf-java] Reading grib2 with LambertConformal_Projection -> lat / lng
    • From: Sean Arms