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• Filename conventions
• Data Format
• Interpolation
• IDL and MATLAB Read Routines

• COMPOSITION is a description of the composition of the measured sample, (all lower case except if a chemical formula e.g. H2O)
  If the material is birefringent then the ordinary and extraordinary rays are separated as follows:
  composition_O_Author_year.ri
  composition_E_Author_year.ri
  If the material has three optical axes then the following notation is used:
  composition_X_Author_year.ri
  composition_Y_Author_year.ri
  composition_Z_Author_year.ri
• NAME/LAB is either the name of the first author of the published paper from which the data is taken or the name of the scientist or laboratory that provided the data, (lower case but capitalize first letter, i.e. as in 'Title')
• YEAR is the year of publication or data release.

• A header describing the file. Header lines start with the '#' character and define Keywords. i.e.
  #Keyword = some text
• The data which is formatted into columns which are separated by white space (tabs or spaces).

1. Legitimate Keywords are
   • FORMAT
   • DESCRIPTION
   • DISTRIBUTEDBY
   • SUBSTANCE
   • SAMPLEFORM
   • TEMPERATURE
   • CONCENTRATION
   • REFERENCE
   • SOURCE
   • CONTACT
   • COMMENT
2. The only compulsory Keyword is FORMAT which defines the columns of data. Valid FORMAT components are:
   • WAVL which indicates the column contains the spectral location in wavelength (μm)
   • WAVN which indicates the column contains the spectral location in wavenumbers (cm^-1)
   • N which indicates the column contains the real part of the refractive index
   • DN which indicates the column contains the uncertainty in the real part of the refractive index
   • K which indicates the column contains the imaginary part of the refractive index (always positive)
   • DK which indicates the column contains the uncertainty in the real imaginary part of the refractive index
   Examples
   #FORMAT = WAVL N DN K DK
   implies there are five columns: wavelength, real part, real error, imaginary part, imaginary error
   #FORMAT = WAVN K DK
   implies there are three columns: wavenumber, imaginary part, imaginary error
   
3. Each row must contain data for all included columns. For example if
   FORMAT = WAVL N K
   and K (the imaginary part) goes to zero at some wavelength you cannot stop giving a value for K. In this case you would just repeat zeros.
4. K is generally positive. There are some cases where K is slightly negative due to measurement noise. In this cases read_ri forces the value to zero.
5. As the the number of Keyword definitions can vary the length of the number of header lines can vary but must be at least one (to define FORMAT).
6. To avoid very long lines Keyword definitions can extend over more than one line by using '##' as the continuation code. For example

   #COMMENT = This is a very long comment split
   ## over more than one line

7. Aria will compile and read_ri.pro will work if only the FORMAT Keyword is present however you are strongly encouraged to define the DESCRIPTION and REFERENCE Keywords.
8. Additional keywords can be included but will be ignored in forming Aria and by read_ri.pro.
9. In compiling Aria the fields are passed as HTML so use HTML format commands if you want to include subscripts, Greek characters etc.

PCHIP	SPLINE

Note that collections of files will have to be unpacked before they can be read.