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qddiff.md

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qddiff is a simple program for analyzing differences between two querydata. The command is used in routines for example for analyzing which parameters and timesteps have changed in the forecasts so that the routine can decide which images have to be rendered again. The CPU savings in a very large production system can be very significant if only a small part of the forecast has been changed.

Command line

The command line syntax is

qddiff [options] querydatafile1 querydatafile2 outputfile
qddiff [options] querydatadir outputfile

If the first parameter is a directory, the two newest files in it are compared.

The available options are:

  • -h
    prints information on command line options
  • -t
    only new timesteps in file are saved to outputfile
  • -p
    only only common times where parameters have changed
  • -v
    verbose mode
  • -V
    verbose analysis of the differences in the files
  • -d
    debug mode (verbose mode goes automatically on) Note that if one does not wish to save the differences between the querydata, for example if only the results if option -V are desired, one can use /dev/null as the outputfile.

Examples

Here is an analysis of what the meteorologist did at Finnish Meteorological Institute when the Scandinavian forecast was edited the last time:

> pwd
/data/pal/querydata/pal/skandinavia15km/pinta_xh
> qddiff -V . /dev/null
0 times were missing from data 1
0 parameters were missing from data 1
0 levels were missing from data 1
11 timesteps were unchanged
56 timesteps were changed
unchanged Pressure
unchanged Temperature
unchanged DewPoint
unchanged Humidity
unchanged WindDirection
unchanged WindSpeedMS
unchanged WindVectorMS
unchanged WindUMS
unchanged WindVMS
CHANGED PrecipitationType in 10 timesteps
CHANGED PrecipitationForm in 10 timesteps
CHANGED TotalCloudCover in 25 timesteps
unchanged KIndex
unchanged PoP
unchanged ProbabilityThunderstorm
CHANGED MiddleAndLowCloudCover in 56 timesteps
CHANGED LowCloudCover in 56 timesteps
CHANGED MediumCloudCover in 1 timesteps
unchanged HighCloudCover
CHANGED RadiationLW in 25 timesteps
CHANGED RadiationGlobal in 19 timesteps
unchanged FogIntensity
CHANGED WeatherSymbol1 in 10 timesteps
CHANGED WeatherSymbol3 in 26 timesteps
CHANGED Precipitation1h in 10 timesteps
unchanged HourlyMaximumGust

From the analysis one can see the meteorologist has edited mainly precipitation and cloudiness, not for example wind or temperature.