f_opendap_simple.f90 File Reference

Simple OPeNDAP example in Fortran. More...

Functions/Subroutines
program	f_opendap_simple

Detailed Description

Simple OPeNDAP example in Fortran.

This is the Fortran equivalent of opendap_simple.c, demonstrating that OPeNDAP remote access works identically in Fortran through the NetCDF-Fortran library.

What this example does:

1. Opens a remote sea surface temperature dataset from test.opendap.org
2. Queries dataset metadata using nf90_inquire
3. Reads information about the 'sst' variable dimensions
4. Reads a small 5x5 spatial subset from the first time step
5. Closes the remote connection

CRITICAL: Indexing differences to understand:

• OPeNDAP constraint expressions in URLs use 0-based indexing [0:2]
• NetCDF-Fortran API uses 1-based indexing: start=(/1, 1, 1/)
• This is automatically handled by the Fortran interface

The example uses the same public test dataset as the C version: sst.mnmean.nc.gz - NOAA Extended Reconstructed Sea Surface Temperature

Learning Objectives:

• Open a remote OPeNDAP dataset from Fortran using nf90_open() with an HTTP URL
• Query dataset metadata (dimensions, variables, attributes) via nf90_inquire()
• Read a spatial subset using start/count arrays with 1-based Fortran indexing
• Understand that OPeNDAP access is transparent — same API as local files

Key Concepts:

• Transparent Remote Access: nf90_open() accepts HTTP URLs just like local paths
• 1-Based Indexing: Fortran start arrays begin at 1, not 0 as in C
• Constraint vs Client Subsetting: This example uses no URL constraints; subsetting is done client-side via start/count in nf90_get_var()
• OPeNDAP Indexing: URL constraint expressions use 0-based indexing, but Fortran API calls use 1-based — the library handles the translation

Prerequisites:

• f_simple_2D.f90 - Basic Fortran NetCDF operations
• opendap_simple.c - C equivalent for comparison
• A NetCDF library built with OPeNDAP support

Related Examples:

• opendap_simple.c - C equivalent
• f_opendap_constraint.f90 - Server-side subsetting from Fortran
• f_opendap_subset.f90 - Client-side subsetting patterns from Fortran

Compilation:

gfortran -o f_opendap_simple f_opendap_simple.f90 -lnetcdff -lnetcdf

Usage:

./f_opendap_simple

Expected Output:

• Opens remote SST dataset and prints dimension/variable counts
• Reads and displays a 5x5 spatial subset from the first time step

Note

Companion code for "The NetCDF Developer's Handbook: The Authoritative Guide to Writing High-Performance Programs for Scientific Data Management, Second Edition" (https://www.amazon.com/dp/B0H7Q1Z75L)

Author

Edward Hartnett

Date

6/15/26

Function/Subroutine Documentation

f_opendap_simple()

program f_opendap_simple