CDM Section Specification

Syntax

Array sections can be specified with Fortran 90 array section syntax, using zero-based indexing. For example:

/group1/group2/varName(12:22,0:100:2,:,17)

specifies an array section for a four dimensional variable:

12:22 includes all the elements from 12 to 22 inclusive
0:100:2 includes the elements from 0 to 100 inclusive, with a stride of 2
: includes all the elements
17 includes just the 18th element.

For structures, you can specify nested selectors, e.g. record(12).wind(1:20,:,3) does a selection on the wind member variable of the record structure at index 12. If you don’t specify a section, it means read the entire variable, e.g. record.wind means all the data in all the wind variables in all the record structures.

Formally:

 sectionSpec := selector | selector '.' selector

 selector := varName ['(' sectionSpec ')']
 varName := STRING 
 sectionSpec := dim | dim ',' sectionSpec
 dim := ':' | slice | start ':' end | start ':' end ':' stride


 slice := INTEGER 
 start := INTEGER
 stride := INTEGER
 end := INTEGER
 STRING := String with escaped chars = '.', '/', '(', and ')'

where:

Nonterminals are in lower case, terminals are in upper case, literals are in single quotes.
Optional components are enclosed between square braces '[' and ']'.

TBD:

escape mechanism is currently %xx , mostly following opendap
not sure if any other chars need to be escaped.

Restrictions

A Sequence is a one-dimensional Structure with a variable length, it cannot be subsetted

A variable long name must be used, that is with its group names: /group1/group2/varName

Use

  public Array NetcdfFile.readSection(String variableSection);

Also See:

Fortran 90 Array sections
NCAR NCL Array subscripts : probably generalize using this.

This document is maintained by John Caron and was last updated on May 08, 2008

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