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Re: NetCDF Java 4.2 and Time

On 12/23/2010 10:37 AM, Tom Kunicki wrote:

Hi John,

We just migrated to NetCDF-Java 4.2 and encountered a bunch of unit test failures with files using the following format for time:

<?xml version="1.0" encoding="UTF-8"?>
  <dimension name="time" length="2" />
  <dimension name="lat" length="3" />
  <dimension name="lon" length="4" />
  <dimension name="height" length="5" />
  <attribute name="title" value="testSimpleTZYXGrid Data" />
  <attribute name="Conventions" value="CF-1.4" />
  <variable name="rh" shape="time height lat lon" type="int">
    <attribute name="long_name" value="relative humidity" />
    <attribute name="units" value="percent" />
<attribute name="coordinates" value="lat lon" />
    <values start="10" increment="5" />
  <variable name="time" shape="time" type="int">
<attribute name="units" value="hours" />
    <values start="1" increment="1" />
  <variable name="lat" shape="lat" type="float">
    <attribute name="units" value="degrees_north" />
<values start="40" increment="1" />
  <variable name="lon" shape="lon" type="float">
    <attribute name="units" value="degrees_east" />
    <values start="-90" increment="1" />
  <variable name="height" shape="height" type="float">
    <attribute name="units" value="meters" />
<attribute name="positive" value="up"/>
    <values start="1" increment="1" />

It looks like we need to append something like " since 0001-01-01 00:00:00" to get this to work.   I had to dig through the source as the failure was silent.  An exception was thrown from line 151 of CoordinateAxis1DTime.java and then caught and effectively ignored on line 411 of GridCoordSys.java.    I think the root cause of the issue is that the DateUnit constructor doesn't throw an error with "hours" as a unit even tho subsequent instance method calls will fail.

Looks like the CF spec says a reference time is required, so I guess this is more of an error handling/notification issue...


hmmm, now that im looking closer, this is a tricky one to decide if its in error. technically, theres no requirement that it be a time coordinate, although that is obviously the intention.

actually, we mark it as a "time" axis, even though its not udunit compatible, in order to allow various crappy datasets to be viewed as grids. not sure if thats a mistake, but it would be hard to reverse it.

so, i could give a warning message or something, but probably i have to allow it.

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