mirror of https://github.com/ecmwf/eccodes.git
281 lines
10 KiB
Bash
Executable File
281 lines
10 KiB
Bash
Executable File
#!/bin/sh
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set -e
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dir=$PWD
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toolsDir=../tools/
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dataDir=../data/
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cd $dataDir
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echo "-# The default behaviour for grib_compare without any option is to perform a bit by bit comparison of the two messages. If the messages
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are found to be bitwise different then grib_compare switches to a \"key based\" mode to find out which coded keys are different.
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To see how grib_compare works we first set the shortName=2d (2 metre dew point temperature) in the file
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regular_latlon_surface.grib1\\n
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\\verbatim
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>grib_set -s shortName=2d regular_latlon_surface.grib1 2d.grib1
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\\endverbatim"
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rm -f 2d.grib1 | true
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$toolsDir/grib_set -s shortName=2d regular_latlon_surface.grib1 2d.grib1
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echo "Then we can compare the two fields with grib_compare.\\n"
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echo "\\verbatim
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>grib_compare regular_latlon_surface.grib1 2d.grib1"
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set +e
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$toolsDir/grib_compare regular_latlon_surface.grib1 2d.grib1
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set -e
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echo "\\endverbatim
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In the output we see that the only \"coded\" key with different values in the two messages is indicatorOfParameter which is the
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relevant key for the parameter information.
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The comparison can be forced to be successful listing the keys with different values in the -b option."
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echo "\\verbatim
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>grib_compare -b indicatorOfParameter regular_latlon_surface.grib1 2d.grib1"
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set +e
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$toolsDir/grib_compare -b indicatorOfParameter regular_latlon_surface.grib1 2d.grib1
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set -e
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echo "\\endverbatim
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\n\n"
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echo "-# Two grib messages can be very different because they have different edition, but they can contain the same
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identical information in the header and the same data. To see how grib_compare can help in comparing messages with different edition we
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do
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\\verbatim
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>grib_set edition=2 reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2
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\\endverbatim"
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rm -f regular_latlon_surface.grib2 | true
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$toolsDir/grib_set -s edition=2 reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2
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echo "Then we compare the two fields with grib_compare.\\n"
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echo "\\verbatim
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>grib_compare reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2"
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set +e
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$toolsDir/grib_compare reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2
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set -e
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echo "\\endverbatim
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It is clear that the two messages are coded in a very different way. If we now add the -e option, the tool will compare only the
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higher level information common between the two messages."
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echo "\\verbatim
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>grib_compare -e reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2"
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set +e
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$toolsDir/grib_compare -e reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2
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set -e
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echo "\\endverbatim
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The comparison is successful because the two messages contain the same information coded in two different ways.
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We can display the list of keys used by grib_compare adding the option -v (verbose)."
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echo "\\verbatim
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>grib_compare -ve reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2"
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set +e
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$toolsDir/grib_compare -ve reduced_gaussian_model_level.grib1 reduced_gaussian_model_level.grib2
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set -e
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echo "\\endverbatim
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For each key the type used in the comparison is reported and for the floating point keys also the tolerance used
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is printed.
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\n\n"
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echo "-# Some options are provided to compare only a set of keys in the messages. The option -H is used to compare only the headers
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coded in the message, it doesn't compare the data values.
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The option \"-c key1:[i/d/s/n],key2:[i/d/s/n],... \" can be used to
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compare a set of keys or namespaces. The letter after the colon is optional and it is used to force the
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type used in the comparison which is otherwise assumed to be the native type of the key.
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The possible types are:
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- :i -> integer
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- :d -> floating point (C type double)
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- :s -> string
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- :n -> namespace.
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.
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When the type \"n\" is used all the set of keys belonging to the specified namespace
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are compared assuming their own native type.
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To illustrate how these options work we change the values coded in
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a message using grib_filter with the following rules file (see \ref grib_filter). "
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echo "\\verbatim
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set bitsPerValue=10;
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set values={1,2.5,3,4,5,6,70};
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write \"first.grib1\";
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set values={1,2.5,5,4,5,6,70};
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write \"second.grib1\";
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\\endverbatim"
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cat > x.rules <<EOF
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set bitsPerValue=10;
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set values={1,2.5,3,4,5,6,70};
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write "first.grib1";
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set values={1,2.5,5,4,5,6,70};
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write "second.grib1";
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EOF
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$toolsDir/grib_filter x.rules reduced_gaussian_model_level.grib1
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rm -f x.rules
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echo "We first compare the two files using the -H option (only headers are compared)."
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echo "\\verbatim
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>grib_compare -H first.grib1 second.grib1"
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set +e
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$toolsDir/grib_compare -H first.grib1 second.grib1
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set -e
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echo "\\endverbatim
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The comparison is successful because the data are not compared.
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To compare only the data we have to compare the \"data namespace\"."
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echo "\\verbatim
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>grib_compare -c data:n first.grib1 second.grib1"
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set +e
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$toolsDir/grib_compare -c data:n first.grib1 second.grib1
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set -e
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echo "\\endverbatim
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The comparison is showing that one of seven values is different in a comparison
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with the (default) absolute tolerance=0. We can change the tolerance with the -A option:"
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echo "\\verbatim
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>grib_compare -A 2 -c data:n first.grib1 second.grib1"
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set +e
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$toolsDir/grib_compare -A 2 -c data:n first.grib1 second.grib1
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set -e
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echo "\\endverbatim
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and we see that the comparison is successful if the absolute tolerance is set to 2.
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We can also set the relative tolerance for each key with the option -R:"
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echo "\\verbatim
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>grib_compare -R packedValues=0.4 -c data:n first.grib1 second.grib1"
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set +e
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$toolsDir/grib_compare -R packedValues=0.4 -c data:n first.grib1 second.grib1
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set -e
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echo "\\endverbatim
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and we get again a successful comparison because the relative tolerance is bigger than the
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relative absolute difference of two corresponding values.
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Another possible choice for the tolerance is to be equal to the packingError,
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which is the error due to the packing algorithm. If we change the decimalPrecision of
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a packed field we introduce a packing error sometimes bigger than the original
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packing error."
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echo "\\verbatim
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>grib_set -s changeDecimalPrecision=0 first.grib1 third.grib1"
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set +e
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$toolsDir/grib_set -s changeDecimalPrecision=0 first.grib1 third.grib1
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set -e
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echo "\\endverbatim
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and we compare the two fields using the -P option (tolerance=packingError)."
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echo "\\verbatim
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>grib_compare -P -c data:n first.grib1 third.grib1"
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set +e
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$toolsDir/grib_compare -P -c data:n first.grib1 third.grib1
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set -e
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echo "\\endverbatim
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the comparison is successful because their difference is within the biggest of
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the two packing error. With the option -P the comparison is failing only
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if the original data coded are different, not if the packing precision is
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changed. If we try again to compare the fields without the -P option:"
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echo "\\verbatim
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>grib_compare -c data:n first.grib1 third.grib1"
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set +e
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$toolsDir/grib_compare -c data:n first.grib1 third.grib1
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set -e
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echo "\\endverbatim
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we see that some values are different and that the maximum absolute differenc
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is close to the biggest packing error (max diff=0.48 packingError=0.5).
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The packing error was chosen to be 0.5 by setting decimalPrecision to 0 which
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means that we don't need to preserve any decimal figure.\n\n"
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echo "-# When we already know that the fields are not numerically identical, but have
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similar statistical characteristics we can compare their statistics namespaces:"
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echo "\\verbatim
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>grib_compare -c statistics:n first.grib1 third.grib1"
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set +e
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$toolsDir/grib_compare -c statistics:n first.grib1 third.grib1
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set -e
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echo "\\endverbatim
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and we see that maximum, minimum, average, standard deviation, skewness and kurtosis are compared.
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While the values are different by 0.48 the statistics comparison shows that the difference in
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the statistical values is never bigger than 0.052"
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echo "\\verbatim
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>grib_compare -A 0.052 -c statistics:n first.grib1 third.grib1"
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set +e
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$toolsDir/grib_compare -A 0.052 -c statistics:n first.grib1 third.grib1
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set -e
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echo "\\endverbatim
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The statistics namespace is available also for spherical harmonics data and provides
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information about the field in the geographic space computing them in the spectral space for
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performance reasons.
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\n\n"
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echo "-# When a file contains several fields and some keys are different, it is useful to have a summary
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report of the keys found different in the messages. This can be obtained with the option -f.
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We change few keys in a file:"
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echo "\\verbatim
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>grib_set -w typeOfLevel=surface -s step=48 tigge_pf_ecmwf.grib2 out.grib2"
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set +e
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$toolsDir/grib_set -w typeOfLevel=surface -s step=48 tigge_pf_ecmwf.grib2 out.grib2
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set -e
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echo "\\endverbatim
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and comparing with the -f option:"
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echo "\\verbatim
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>grib_compare -f tigge_pf_ecmwf.grib2 out.grib2"
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set +e
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$toolsDir/grib_compare -f tigge_pf_ecmwf.grib2 out.grib2 | head -11
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echo "... output deleted "
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$toolsDir/grib_compare -f tigge_pf_ecmwf.grib2 out.grib2 | tail -10
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set -e
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echo "\\endverbatim
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we get a list of all the different messages in the files and a summary report
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of the different keys.
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\n\n"
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rm -f out.grib2
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echo "-# We can change the order of the messages in a file using grib_copy with the
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-B option:"
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echo "\\verbatim
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>grib_copy -B typeOfLevel tigge_pf_ecmwf.grib2 out.grib2"
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set +e
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$toolsDir/grib_copy -B typeOfLevel tigge_pf_ecmwf.grib2 out.grib2
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set -e
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echo "\\endverbatim
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If we now compare the two files:"
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echo "\\verbatim
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>grib_compare -f tigge_pf_ecmwf.grib2 out.grib2"
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set +e
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$toolsDir/grib_compare -f tigge_pf_ecmwf.grib2 out.grib2 | head -20
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echo "... very long output "
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set -e
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echo "\\endverbatim
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the comparison is failing because of the different order of the messages.
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We can use the -r option to compare the files assuming that the messages are not in the
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same order:"
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echo "\\verbatim
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>grib_compare -r tigge_pf_ecmwf.grib2 out.grib2"
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set +e
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$toolsDir/grib_compare -r tigge_pf_ecmwf.grib2 out.grib2
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set -e
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echo "\\endverbatim
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and we have a successful comparison because for each message in the first file an identical
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message is found in the second file. This option should be used carefully as it is
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very time expensive.
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\n\n"
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rm -f first.grib1 second.grib1 third.grib1 out.grib2
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cd $dir
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