(CDF library Version 3.5.0.0 ) for IDL 6.2 and later. This page contains the beta IDL-CDF patch ( Version 3.5.0.0) based on Recsize, is added to yield the final offset value.CDF Patch for IDL 6.2 and later, including IDL 7.* and 8.* The product of the record number, ’coord’, and the record size, Finally, if the variable is a record variable, Of the coord and product vectors times the size, in bytes, of eachĭatum for the variable. Of the desired variable (its begin field) added to the inner product Then the offset of the value from theīeginning of the file is just the file offset of the first data value Let coord be the array of coordinates (dimension indices, zero-based) Variable, the value of vsize is just 72, since this is already a ForĮxample, in the non-record variable above, the value of the vsizeįield is 212 (210 rounded up to a multiple of 4). Multiple of 4, is the variable size, vsize, in the grammar above.
To calculate the offset (position within the file) of a specified data value, let external_sizeof be the external size in bytes of one data value of the appropriate type for the specified variable, nc_type:Īt this point, the leftmost product, when rounded up to the next NC_DOUBLE := 6 // data is array of IEEE double precision float
NC_FLOAT := 5 // data is array of IEEE single precision float NC_LONG := 4 // data is array of 32 bit signed integer
NC_SHORT := 3 // data is array of 16 bit signed integer NC_CHAR := 2 // data is array of characters, i.e., text NC_BYTE := 1 // data is array of 8 bit signed integer data, padding is with variable's fill-value. See the note below for a special case. n, second record variable for record n. Rec := // Data for first record variable for record Non_recs := // Data for first non-record var, second "record size" is calculated as the sum ofīegin := NON_NEG // Variable start location. size of the type, padded to a four byte product of the dimension sizes times the the amount of space, in bytes, allocated to Vatt_array := att_array // variable-specific attributesĭimid := NON_NEG // Dimension ID (index into dim_array) for variable 0 for scalar, 1 for vector, 2 for nelems is the rank (dimensionality) of the Var := name nelems vatt_array nc_type vsize begin Nc_type := NC_BYTE | NC_CHAR | NC_SHORT | NC_LONG | NC_FLOAT | NC_DOUBLE There can be at most one record dimension. Nelems := NON_NEG // number of elements in following sequenceĭim_size := NON_NEG // If zero, this is the record dimension. Var_array := ABSENT | NC_VARIABLE nelems ĪBSENT := ZERO ZERO // Means array not present (equivalent to Gatt_array := att_array // global attributesĪtt_array := ABSENT | NC_ATTRIBUTE nelems VERSION_BYTE := '\001' // the file format version numberĭim_array := ABSENT | NC_DIMENSION nelems Header := magic numrecs dim_array gatt_array var_array
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