This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
Hi Riccardo, Sorry for the delay in getting back to you. This just slipped through the cracks of our support box. > Description of problem: I STARTED USING IDL TODAY. WHAT I'D LIKE TO DO IS > VERY SIMPLE: I HAVE A GRIB FILE WITH CUMULATED PRECIPITATIONS FROM ECMWF > OPERATIONAL MODEL, AND I WANT TO MAKE A "SIMPLE TIME DIFFERENCE" IN ORDER TO > SEE THE CUMULATED VALUE IN 12 HOURS: T24-T12, T36-T24 AND SO ON. IT APPEARS A > SMALL WINDOWS REQUESTING "TIME1" AND "TIME2", BUT I DON'T UNDERSTAND WHICH > VALUES I HAVE TO PUT INSIDE. THANK YOU VERY MUCH IN ADVANCE. RICCARDO > The latest version of the IDV has a formula Formulas->Grids->Time Steps->Time step difference that takes a grid field and does a difference so that: Data(T) = Data(T)-Data(T-1) Note - the -1 offset is the index of the time, e.g., -3 is not -3 hours but is the time 3 time stpes prior. This is not the absolute time. One can also specify an arbitrary (index) offset using another formula. Attached is a plugin (install it through the Tools->Plugin Manager dialog under its File menu). This has a formula that prompts the user or an offset. It also has a fix to a problem in our released jython library (it call a routine fixedtimeStepDifference not the normal (and broken) timeStepDifference). -Jeff Ticket Details =================== Ticket ID: ELV-470278 Department: Support IDV Priority: Critical Status: Closed
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timestepdifference.jar
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