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That is, all rVariables in a CDF must have the same number of dimensions and dimension sizes. RVariables (or regular variables) are multidimensional arrays of values, each having the same dimensions. In both cases, the default is varying data. Record variance is set using the REC_VARY and REC_NOVARY keywords to CDF_VARCREATE, while dimensional variance is set through the DimVary argument to CDF_VARCREATE. On the other hand, a variable such as longitude may not vary from record to record, but will vary from dimension to dimension. A variable representing “GMT time” will vary from record to record, but not dimension to dimension (since all data are taken simultaneously).
#CDF FILES DOWNLOAD CODE#
For example, consider a data set of simultaneous surface temperatures at a variety of locations, the IDL code for creating the CDF file is included at the end of this section. For reasons of efficiency, CDF uses variances to indicate whether data is unique between records and dimensions. CDF supports two distinct types of variables, rVariables and zVariables. IDL can create CDF files representing any data that can be stored in a zero- to eight-dimensional array. Information in a CDF file consists of attributes (metadata) and collections of data records (variables). CDF_ATTPUT, id, att2_id, time_id, 'GMT' FOR I= 0, 9 DO CDF_VARPUT, id, time_id, 8.+ 0.5 * I, rec_start=I temp_id = CDF_VARCREATE(id, 'Temp',, $ /REC_VARY, /ZVAR, DIMENSIONS=) long_id = CDF_VARCREATE(id, 'Longitude',, $ /REC_NOVARY) lat_id = CDF_VARCREATE(id, 'Latitude',, $ /REC_NOVARY) write 10 temperature records: CDF_VARPUT, id, temp_id, FINDGEN( 2, 3, 10), /ZVARIABLE create longitudes: CDF_VARPUT, id, long_id,, , ] create latitudes: CDF_VARPUT, id, lat_id,, ,] CDF_CLOSE, id Variables and Attributes id = CDF_CREATE( 'Temperature.cdf',, /CLOBBER ) att_id = CDF_ATTCREATE(id, 'Title', /GLOBAL) CDF_ATTPUT, id, att_id, 0, 'My Fancy CDF' att1_id = CDF_ATTCREATE(id, 'Planet', /GLOBAL) CDF_ATTPUT, id, 'Planet', 0, 'Mars' time_id = CDF_VARCREATE(id, 'Time',, $ /REC_VARY) att2_id = CDF_ATTCREATE(id, 'Time Standard', /VARIABLE_SCOPE) times are every half hour starting a 8 am GMT. The following example demonstrates the basic procedure for creating a CDF file. For example, in this code snippet IDL converts the string “12” to a floating-point 12.0 before writing it: varid= CDF_VARCREATE(fileid, 'VarName',$ DIM=,/CDF_FLOAT) CDF_VARPUT, fileid, 'VarName', '12' Reference by variable ID Code Examples Values are converted to the appropriate type before being written to a CDF file.
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If the structure of the CDF file is already known, you do not need to call the inquiry routines-only CDF_OPEN, CDF_ATTGET, CDF_VARGET, and CDF_CLOSE are needed. Optionally, retrieve the names, scope, and other information about the CDF file's attributes. Retrieve the names, types, sizes, and other information about the variables in the CDF file. The following table lists the basic commands needed to read data from a CDF file: CDF_OPENĬall this function to find the general information about the contents of the CDF file.Ĭall this function to obtain further information about the CDF file Write the appropriate data to the CDF file. Optionally, use attributes to describe the data. CDF_CREATE contains a number of keywords which affect the internal format of the new CDF file.ĭefine the variables to be used in the file. The following table lists the basic IDL commands needed to create a new CDF file:Ĭall this procedure to begin creating a new file. IDL’s CDF routines all begin with the prefix “CDF_”. CDF is a product of the National Space Science Data Center (NSSDC). The Common Data Format (CDF) is a file format that facilitates the storage and retrieval of multi-dimensional scientific data. Tip: For information on the current CDF version, enter the following at the IDL prompt: HELP, 'cdf', /DLM