Hey guys,
Let me preface this by stating that I'm running with netcdf-4.2 because
I wasn't able to find the latest 4.2.22 on the download page (if anyone
could point me to the 4.2.22 download I'd appreciate it). I have tried
with the 4.2.20 binaries (which I found on ibiblio) but had the same
problem...
I'm trying to use netcdf-java to process a GRIB v1 RUC file and was
noticing that the returned GridDataset had a value for the Earth's
radius of 6371.229km (i.e. Earth.getRadius() * .001 - the default
value). This is incorrect for GRIB v1, which should have a radius of
6367.47km (i.e. Grib1Tables.getShapeRadius()). Inspecting the source I
was able to make what I believe to be the proper fix, but I'll let you
folks be the judge. The fix spans two files (attached).
The first issue was that the during the process of creating the
GridDataset, the LambertConformal projection is copied using the
constructCopy() method. This method was not, however, copying the
Earth's radius so it was getting the default value (incorrect for GRIB
1).
The second issue was that LambertConformalConic relies on an attribute
"earth_radius" to be in meters, since it does a conversion to km when
creating the projection. In GridHorizCoordSys, however, the
"earth_radius" attribute is set directly from the attribute
"grid_radius_spherical_earth" or "radius_spherical_earth" (depending on
GRIB1 or GRIB2). This value appears to be coming in as km for GRIB1.
So it's already km, then LambertConformalConfic multiplies by 0.001
again (thinking it's meters) and we end up with a very small value for
the radius of the Earth.
I've run my local tests and things appear to be working properly with
these changes. If you guys like these changes, would there be any way
of getting this into the next release?
Thanks in advance for all your help.
Regards,
Nathan Mittler
-
This message is intended only for the addressee and may contain information
that is company confidential or privileged. Any technical data in this message
may be exported only in accordance with the U.S. International Traffic in Arms
Regulations (22 CFR Parts 120-130) or the Export Administration Regulations (15
CFR Parts 730-774). Unauthorized use is strictly prohibited and may be
unlawful. If you are not the intended recipient, or the person responsible for
delivering to the intended recipient, you should not read, copy, disclose or
otherwise use this message. If you have received this email in error, please
delete it, and advise the sender immediately.
-
Attachment:
LambertConformal.java
Description: LambertConformal.java
Attachment:
GridHorizCoordSys.java
Description: GridHorizCoordSys.java
netcdf-java archives: