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title Section Specification
last_updated 2026-06-23
sidebar netcdfJavaTutorial_sidebar
toc false
permalink section_specification_ref.html

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:

  1. 12:22 includes all the elements from 12 to 22 inclusive
  2. 0:100:2 includes the elements from 0 to 100 inclusive, with a stride of 2
  3. : includes all the elements
  4. 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, and 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);