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Extract a selection of fields from a fieldset. The vector supplied as the argument provides the set of indices to be used. For example:
# copies fields 2, 1, 3 of x into y
x = |2, 1, 3|
y = x[i]

Returns the fieldset of the absolute value of the input fieldset at each grid point or spectral coefficient. Missing values are retained, unaltered by the calculation.

Return the fieldset of the arc trigonometric function of the input fieldset at each grid point. Result is in radians. Missing values are retained, unaltered by the calculation.

Returns the fieldset of the cosine of the input fieldset at each grid point. Input values must be in radians. Missing values are retained, unaltered by the calculation.

Returns the number of fields in a fieldset.

Returns the fieldset of the exponential of the input fieldset at each grid point. Missing values are retained, unaltered by the calculation.

Returns a fieldset with integer data converted into floating point data for more accurate computations. The second parameter is optional; if given it defines the number of bits used for packing the float values. If not given, the default value of 24 is used (unless function gribsetbits(number) has been called to set it).

Returns the fieldset of the integer part of the input fieldset at each grid point or spectral coefficient. Missing values are retained, unaltered by the calculation.

Returns the fieldset of the integer part of the input fieldset at each grid point or spectral coefficient. This function modifies the resulting GRIB header to be of integer data type. Missing values are replaced with LONG_MAX. This function was used in Metview 3 to enable the plotting of certain types of satellite imagery.

Returns the fieldset of the natural log of the input fieldset at each grid point. Missing values are retained, unaltered by the calculation.

Returns the fieldset of the log base 10 of the input fieldset at each grid point. Missing values are retained, unaltered by the calculation.

Returns the fieldset of the negative of the input fieldset at each grid point or spectral coefficient. The same as (- fieldset). Missing values are retained, unaltered by the calculation.

Returns the fieldset of the sign of the values of the input fieldset at each grid point or spectral coefficient : -1 for negative values, 1 for positive and 0 for null values. Missing values are retained, unaltered by the calculation.

Returns the fieldset of the sine of the input fieldset at each grid point. Input fieldset must have values in radians. Missing values are retained, unaltered by the calculation.

Returns the fieldset of the square root of the input fieldset at each grid point. Missing values are retained, unaltered by the calculation.

Return the tangent of the input fieldset at each grid point. Input fieldset must have values in radians. Missing values are retained, unaltered by the calculation.

For each field in the fieldset, this function calculates the sum of all the values of the field. If there is only one field in the fieldset, a number is returned. Otherwise, a list of numbers is returned. Only non-missing values are considered in the calculation. If there are no valid values, the function returns nil for that field.

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Note that the average() function does not return the physically correct average of the field but merely the average of all field values. To get the physically correct average value of a field, use the integrate() function (which employs a cosine latitude weighting)

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For the above example, each value returned (representing the mean at latitude Lat ) is the mean of non-missing values in those grid points whose latitude coordinate is between Lat-1.25 and Lat+1.25 (1.25 is 2.5/2), i.e. within a latitude belt with width of 2.5 degrees, centered around Lat.

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Each value returned (representing the mean at longitude Lon ) is a mean of non-missing values in those grid points whose longitude coordinate is between Lon-2.5 and Lon+2.5 (2.5 is 5/2), in the belt between 30N and 30S.

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The bearing is the angle between the Northward meridian going through the reference point and the great circle connecting the reference point and the given gridpoint.  It is measured in degrees clockwise from North. If a gridpoint is located on the same latitude as the reference point the bearing is regarded constant: it is either 90° (East) or 270° (West). If the gridpoint is co-located with the reference point the bearing is set to a missing value.

Returns the base dates (including the time components) of the given fields. If the fieldset has only one field, a date is returned; otherwise a list of dates is returned.

Returns a copy of the input fieldset (first argument) with zero or more of its values replaced with grib missing value indicators. If the second argument is a number, then any value equal to that number in the input fieldset is replaced with the missing value indicator. If the second argument is another fieldset with the same number of fields as the first fieldset, then the result takes the arrangement of missing values from the second fieldset. If the second argument is another fieldset with one field, the arrangement of missing values from that field are copied into all fields of the output fieldset. See also nobitmap .

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z = corr_a (x, y)
z = covar_a (x, y) / (sqrt(var_a(x)) * sqrt(var_a(y)))

For each field in the input fieldset, this function creates a field where each grid point has the value of the cosine of its latitude.

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A missing value in either input fieldset will result in a missing value in the corresponding place in the output fieldset.

Computes the covariance of two fieldsets over a weighted area. The area, if specified, is a list of numbers representing North, West, South, East. If the area is not specified, the whole field will be used in the calculation. The result is a number for a single field, or a list for a multi-field fieldset.

Returns a list of definitions - one for each field in the fieldset. Each definition provides the following members: the index of the field in the fieldset, the number of missing values, the number of values that are present and the proportion of each. The following example illustrates how to use the function.

fs = read (strGribFile)
listdefInfo = datainfo (fs)
loop defInfo in listdefInfo
     print ("Field index : ", defInfo.index)
     print ("Number of values present : ", defInfo.number_present)
     print ("Number of values missing : ", defInfo.number_missing)
     print ("Proportion values present : ", defInfo.proportion_present)
     print ("Proportion values missing : ", defInfo.proportion_missing)
end loop

Returns a fieldset with the value in each grid point being the direction computed from the given U and V fieldsets; the first input fieldset is assumed to be the East-West (U) component and the second the North-South (V) component. The resulting numbers are directions, in degrees clockwise from North, where a value of 0 represents a wind from the North and a value of 90 represents a wind from the East.

Returns a fieldset with the value in each grid point being the distance in meters from the given geographical location. The location may be specified by supplying either two numbers (latitude and longitude respectively) or a 2-element list containing latitude and longitude in that order. The location should be specified in degrees.

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A missing value in either input fieldset will result in a missing value in the corresponding place in the output fieldset.

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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. If the input fields are horizontal wind components the GRIB paramId of the resulting field is set to 155 (=divergence). Please note that this function is only implemented for regular latitude-longitude grids.

Returns a fieldset with the specified number of copies of the field in the input fieldset. The input fieldset must contain only one field.

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• • if there is a third argument, and it is a list of four numbers (lat/long coordinates) defining a geographical area - [North,West,South,East] , returns a list of locations within that area where the field values are within the interval [a, b]
  • if there is a third argument, and it is a mask field, returns a list of locations within the area defined by the mask (ie, where the mask gridpoints are non-zero) where the fieldset values are within the interval [a, b]

fieldset

Computes the zonal (from West to East) partial derivative of each field in the fieldset. The computations for a field f are based on the following formula:

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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. Please note that this function is only implemented for regular latitude-longitude grids.

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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. Please note that this function is only implemented for regular latitude-longitude grids.

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If the input fieldset has more than one field, the result is a list of lists, one for each field. Note that this function accumulates its results between fields in a fieldset.

Computes the geostrophic wind from geopotential fields defined on pressure levels.  For a given z geopotential field the computation of the geostrophic wind components is based on the following formulas:

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The derivatives are computed with a second order finite-difference approximation. The resulting fieldset contains two fields for each input field: the u and v geostrophic wind components. In each output field the points close to the poles and the Equator are bitmapped (they contain missing values). Please note that this function is only implemented for regular latitude-longitude grids.

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abs(data-value) <= threshold

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[[1,ecmf,1000,0],[1,ecmf,500,0],[1,ecmf,100,0],[1,ecmf,1000,48],[1,ecmf,500,48],[1,ecmf,100,48]]
[[1,1,1,1,1,1],[98,98,98,98,98,98],[1000,500,100,1000,500,100],[0,0,0,48,48,48]]

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a = read('/x/y/z/data_in_gg.grb')
pl = grib_get_long_array (a, 'pl')
print (count(pl))
print (pl)

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f = grib_set(f, ["date", 20150601,       # integer
                 "time", 0600,           # integer
                 "stepType", "avg",      # string
                 "startStep", 0 ,        # integer
                 "endStep", 31,          # integer
                 "unitOfTimeRange", "D", # string
                 "longitudeOfLastGridPointInDegrees"])  100.5  #  double

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If applied to a multi-field fieldset, then all fields are modified.

This function sets the number of GRIB packing bits to the value given (eg 8, 10, 16), and returns the previously used internal value. This function is particularly useful when dealing with 10-bit satellite images as these require GRIB packing to be set to 10 bits.

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GRIB: 1,3,5,5
      2,4,5,5
      1,0,3,1

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Generates a set of geopoints from a field. The first field of the input fieldset is used. The field is interpolated for each position of the geopoints given as a second parameter. The method used is bilinear interpolation. The output geopoints take their date, time and level from the fieldset. Where it is not possible to generate a sensible value due to lack of valid data in the fieldset, the internal geopoints missing value is used (this value can be checked for with the built-in variable geo_missing_value or removed with the function remove_missing_values). Note that a similar function, nearest_gridpoint() , also exists.

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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. Please note that this function is only implemented for regular latitude-longitude grids.

This function returns the grid point latitudes as a vector. If the fieldset contains more than one field it returns a list of vectors. Each of these vectors contains as many elements as grid points in each field.

This function returns the grid point longitudes as a vector. If the fieldset contains more than one field it returns a list of vectors. Each of these vectors contains as many elements as grid points in each field.

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Any missing values in the first fieldset will cause the function to fail with a `value out of range' error message.

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The resulting mask field can be used in the integrate() function.

Returns the fieldset of maximum (minimum) value of the input fieldset at each grid point or spectral coefficient. A missing value in either input fieldset will result in a missing value in the corresponding place in the output fieldset.

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Returns geopoints of maximum (minimum) of the fieldset value and the geopoint value at each grid point or spectral coefficient. Missing values, either in the fieldset or in the original geopoints variable, result in a value of geo_missing_value .

Returns the maximum (minimum) value of all the values of all the fields of the fieldset. The versions that take a list as a second parameter require a geographical area (north, west, south, east); only points within this area will be included in the calculation. Only non-missing values are considered in the calculation. If there are no valid values, the function returns nil.

Generates a matrix containing the values of the input field, or a list of matrices if there are more than one field in the fieldset. Only works with regular lat/long grids.

Computes the mean field of a fieldset. A missing value in any field will result in a missing value in the corresponding place in the output fieldset. With n fields in the input fieldset, if xik is the ith value of the kth input field and yi is the ith value of the resulting field, the formula can be written :

Takes a fieldset as its parameter and computes the mean for each line of constant latitude. The result is a fieldset where the value at each point is the mean of all the points at that latitude. Missing values are excluded; if there are no valid values, then the grib missing value indicator will be returned for those points.

Merge several fieldsets. The same as the operator &. The output is a fieldset with as many fields as the total number of fields in all merged fieldsets. Merging with the value nil does nothing, and is used to initialise when building a fieldset from nothing.

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Generates a set of geopoints from a field. The first field of the input fieldset is used. The result is a set of geopoints whose values are those of the nearest gridpoints in the field to the geopoints given as a second parameter. Where it is not possible to generate a sensible value due to lack of valid data in the fieldset, the internal geopoints missing value is used (this value can be checked for with the built-in variable geo_missing_value or removed with the function remove_missing_values). Note that a similar function, interpolate() , also exists.

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fs = read (strGribFile)
listdef = nearest_gridpoint_info(fs, 51.46, -1.33)
loop ngp in listdef
     print ("Value : ", ngp.value)
     print ("Latitude : ", ngp.latitude)
     print ("Longitude : ", ngp.longitude)
end loop

Returns a copy of the input fieldset (first argument) with all of its missing values replaced with the number specified by the second argument. See also bitmap .

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Missing values in the lnsp field are retained in the output fieldset.

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The name of this function is derived from the fact that it creates a "round mask" or a "radius mask".

Computes the root mean square of a fieldset. A missing value in any field will result in a missing value in the corresponding place in the output fieldset. With n fields in the input fieldset, if x_i ^k is the i^th value of the k^th input field and y_i is the i^th value of the resulting field, the formula can be written :

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y = rms(x)
y = sqrt(mean(x*x))

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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. Please note that this function is only implemented for regular latitude-longitude grids.

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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. Please note that this function is only implemented for regular latitude-longitude grids.

Creates a new fieldset with all the fields' values replaced by those supplied. If supplied as a single vector, the values are set in all fields; if a list of vectors is supplied then there must be the same number of vectors as there are fields in the fieldset. The default behaviour is to produce an error if the input fieldset and vector have different numbers of values. If, however, a third parameter (set to the string 'resize') is passed to the function, the resulting fieldset will instead be resized to have the same number of values as the input vector - this can be useful when creating a new fieldset from a template. Missing values in the vector(s) are retained as missing values in the fieldset.

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# Computes absolute vorticity from vorticity
omega = 2 * pi / 86400
coriolis = 2 * omega * sinlat(vort)
absvort = vort + coriolis

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The third argument specifies a sorting direction. This can be a string (">" or "<") or a list ([">", "<", ">",...]). If it is a string, the sorting direction it specifies applies to all sorting keys specified in the second argument. If it is a list, then the second argument must also be a list with the same number of elements - the sorting directions apply to each sorting key specified.

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y = stdev(x)
y = sqrt(mean(x*x)-mean(x)*mean(x))
y = sqrt(var(x))

Computes the standard deviation over a weighted area. The area, if specified, is a list of numbers representing North, West, South, East. If the area is not specified, the whole field will be used in the calculation. The result is a number for a single field, or a list for a multi-field fieldset.

Computes the sum of a fieldset. The result is a single-field fieldset. A missing value in any field will result in a missing value in the corresponding place in the output fieldset. With n fields in the input fieldset, if xik is the ith value of the kth input field and yi is the ith value of the resulting field, the formula can be written :

Returns the indexes of the four gridpoints surrounding the given location, ordered by increasing distance from the target point. If a list is given, it must contain two numbers - latitude and longitude. If two numbers are given, the first is the latitude, the second the longitude. The field must be a gridded field. If the fieldset has only one field, a number is returned; otherwise a list is returned. Where it is not possible to generate a sensible value due to lack of valid data in the fieldset, nil is returned.

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Missing values in the lnsp field are retained in the output fieldset.

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Missing values in the lnsp field are retained in the output fieldset.

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Missing values in the lnsp field are retained in the output fieldset.

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A missing value in any field will result in a missing value in the corresponding place in the output fieldset.

The function computes:

Image Removed

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\int_{bottom}^{top} f \frac{dp}{g}

where

• • f is the fieldset

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• • p is the pressure

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• • g is the acceleration of gravity (9.81 m/s²).

Returns the valid dates (including the time components) of the given fields. If the fieldset has only one field, a date is returned; otherwise a list of dates is returned.

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# x is a fieldset of n fields
xgrid = values(x)
field1_values = xgrid[1]
gridpoint1 = field1_values[1]

# or equivalently
gridpoint1 = xgrid[1][1]

Computes the variance of a fieldset. A missing value in any field will result in a missing value in the corresponding place in the output fieldset. With n fields in the input fieldset, if xik is the ith value of the kth input field and yi is the ith value of the resulting field, the formula can be written :

Note that the following lines are equivalent :

y = var(x)
y = mean(x*x)-mean(x)*mean(x)

Computes the variance over a weighted area. The area, if specified, is a list of numbers representing North, West, South, East. If the area is not specified, the whole field will be used in the calculation. The result is a number for a single field, or a list for a multi-field fieldset.

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This function performs a vertical integration of the input fieldset, which must contain a range of model levels for the same parameter. A missing value in any field will result in a missing value in the corresponding place in the output fieldset. If the function is called with the fieldset as its single argument, it must also contain the logarithm of the surface pressure (lnsp ). If the function is called with two parameters, the first one is a fieldset containing an lnsp field, the second one is the multi-level fieldset.

The function computes :

Image Removed

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\int_{bottom}^{top} f \frac{dp}{g}

where

• • f is the fieldset

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• • p is the pressure

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• • g is the acceleration of gravity (9.81 m/s²).

The following example computes the total amount of liquid water in the atmosphere by integrating the cloud liquid water content (clwc ) over all levels of the model :

# Retrieve clwc
clwc = retrieve(
   levtype : "ml",
   levelist : [1,"to",31],
   param : "clwc",
   date : -1,
   grid : [2.5,2.5]
)

# Retrieve lnsp
lnsp = retrieve(
   levtype : "ml",
   levelist : 1,
   param : "lnsp",
   date : -1,
   grid : [2.5,2.5]
)

# Integrate the field
x = vertint(lnsp,clwc)
plot(x)

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