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Unidata / netcdf-java

The Unidata netcdf-java library
https://docs.unidata.ucar.edu/netcdf-java/current/userguide/index.html
BSD 3-Clause "New" or "Revised" License
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Fix rounding when computing time offsets #1242

Closed tdrwenski closed 11 months ago

tdrwenski commented 11 months ago

Description of Changes

Accessing MRMS data through NCSS leads to NaNs for all values at certain times. This happens due to the computed offset being incorrect (in CoordsSet::addAdjustedTimeCoords), due to the fact that CalendarPeriod::subtract does not have the property subtract(a, b) = - subtract(b, a). This error was introduced by https://github.com/Unidata/netcdf-java/pull/1099, where I changed the rounding from (int) to Math.floor. Of course, we could fix this issue at the call site of subtract, but it seems less error prone to fix subtract itself. There are two ways to fix this-- go back to casting to int or use Math.round. In the MRMS data I was looking at, the offsets are 0.0, 1.99, 4.0, ... so it just makes more sense to me to round these to 0, 2, 4 rather than truncate to ints.

This change again messes up interval lengths when the reftime is after the start of the interval. This is fixed by the change in TimeCoordIntvDateValue::convertReferenceDate.

tdrwenski commented 11 months ago

Passing on Jenkins: https://jenkins-aws.unidata.ucar.edu/view/Users/job/tara-netcdf-java/29/