ERDDAP > RESTful Web Services

Accessing ERDDAP's RESTful Web Services

ERDDAP is both:

• A web application – a web page with a form that humans with browsers can use (in this case, to get data, graphs, or information about datasets).
   
• A RESTful web service – a URL that computer programs can use (in this case, to get data, graphs, and information about datasets).

For every ERDDAP web page with a form that you as a human with a browser can use, there is a
corresponding ERDDAP web service that is designed to be easy for computer programs and scripts to use. For example, humans can use this URL to do a Full Text Search for interesting datasets:
http://erddap.digitalocean.ie/erddap/search/index.html?page=1&itemsPerPage=1000&searchFor=temperature
By changing the file extension in the URL from .html to .json (or .csv, or .htmlTable, or .jsonlCSV1, or .xhtml, ...):
http://erddap.digitalocean.ie/erddap/search/index.json?page=1&itemsPerPage=1000&searchFor=temperature
we get a URL that a computer program or JavaScript script can use to get the same information in a more computer-program-friendly format like JSON.

Build Things on Top of ERDDAP

There are many features in ERDDAP that can be used by computer programs or scripts that you write. You can use them to build other web applications or web services on top of ERDDAP, making ERDDAP do most of the work! So if you have an idea for a better interface to the data that ERDDAP serves or a web page that needs an easy way to access data, we encourage you to build your own web application, web service, or web page and use ERDDAP as the foundation. Your system can get data, graphs, and other information from ERD's ERDDAP or from other ERDDAP installations, or you can set up your own ERDDAP server, which can be publicly accessible or just privately accessible.

RESTful URL Requests

Requests for user-interface information from ERDDAP (for example, search results) use the web's universal standard for requests: URLs sent via HTTP GET. This is the same mechanism that your browser uses when you fill out a form on a web page and click on Submit. To use HTTP GET, you generate a specially formed URL (which may include a query) and send it with HTTP GET. You can form these URLs by hand and enter them in the address text field of your browser (for example,
http://erddap.digitalocean.ie/erddap/search/index.json?page=1&itemsPerPage=1000&searchFor=temperature)
Or, you can write a computer program or web page script to create a URL, send it, and get the response. URLs via HTTP GET were chosen because

• They are simple to use.
• They work well.
• They are universally supported (in browsers, computer languages, operating system tools, etc).
• They are a foundation of Representational State Transfer (REST) and Resource Oriented Architecture (ROA).
• They facilitate using the World Wide Web as a big distributed application, for example via mashups and AJAX applications.
• They are stateless, as is ERDDAP, which makes the system simpler.
• A URL completely define a given request, so you can bookmark it in your browser, write it in your notes, email it to a friend, etc.

Percent Encoding

In URLs, some characters are not allowed (for example, spaces) and other characters have special meanings (for example, '&' separates key=value pairs in a query). When you fill out a form on a web page and click on Submit, your browser automatically percent encodes the special characters in the URL (for example, space becomes %20), for example,
http://erddap.digitalocean.ie/erddap/search/index.html?page=1&itemsPerPage=1000&searchFor=temperature%20wind%20speed
But if your computer program or script generates the URLs, it probably needs to do the percent encoding itself. If so, then probably all characters other than A-Za-z0-9_-!.~'()* in the query's values (the parts after the '=' signs) need to be encoded as %HH, where HH is the 2 digit hexadecimal value of the character, for example, space becomes %20. Characters above #127 must be converted to UTF-8 bytes, then each UTF-8 byte must be percent encoded (ask a programmer for help). Programming languages have tools to do this (for example, see Java's java.net.URLEncoder and JavaScript's encodeURIComponent()) and there are websites that percent encode/decode for you.

Response File Types

Although humans using browsers want to receive user-interface results (for example, search results) as HTML documents, computer programs often prefer to get results in simple, easily parsed, less verbose documents. ERDDAP can return user-interface results as a table of data in these common, computer-program friendly, file types:

• .csv - a comma-separated ASCII text table. (more info)
• .htmlTable - an .html web page with the data in a table. (more info)
• .itx - an Igor Text File with a wave for each column of data. (more info)
• .json - a table-like JSON file. (more info or ERDDAP-specific info)
• .jsonlCSV1 - a "Better than CSV" JSON Lines file with column names on the first line. (more info)
• .jsonlCSV - a "Better than CSV" JSON Lines file with no column names. (more info)
• .jsonlKVP - a JSON Lines file with Key:Value pairs. (more info)
• .mat - a MATLAB binary file. (more info)
• .nc - a flat, table-like, NetCDF-3 binary file. (more info)
• .nccsv - a flat, table-like, NetCDF-like, ASCII CSV file. (more info)
• .tsv - a tab-separated ASCII text table. (more info)
• .xhtml - an XHTML (XML) file with the data in a table. (more info)

In every results table format (except .jsonlKVP, where column names are on every row):

• Each column has a column name and one type of information.
• The first row of the table has the column names.
• Subsequent rows have the information you requested.

The content in these plain file types is also slightly different from the .html response — it is intentionally bare-boned so that it is easier for a computer program to work with.

A Consistent Data Structure for the Responses
All of the user-interface services described on this page can return a table of data in any of the common file formats listed above. Hopefully, you can write just one procedure to parse a table of data in one of the formats. Then you can re-use that procedure to parse the response from any of these services. This should make it easier to deal with ERDDAP.

.csv and .tsv Details

• If a datum in a .csv file has internal double quotes or commas, ERDDAP follows the .csv specification strictly: it puts double quotes around the datum and doubles the internal double quotes.
• Special characters in a .csv or .tsv file are encoded like JSON backslash-encoded characters: \n (newline), \\ (backslash), \f (formfeed), \t (tab), \r (carriage return) or with the \uhhhh syntax.

jsonp
Requests for .json files may now include an optional jsonp request by adding "&.jsonp=functionName" to the end of the query. Basically, this tells ERDDAP to add "functionName(" to the beginning of the response and ")" to the end of the response. The first character of functionName must be an ISO 8859 letter or "_". Each optional subsequent character must be an ISO 8859 letter, "_", a digit, or ".". If originally there was no query, leave off the "&" in your query.

griddap and tabledap Offer Different File Types
The file types listed above are file types ERDDAP can use to respond to user-interface types of requests (for example, search requests). ERDDAP supports a different set of file types for scientific data (for example, satellite and buoy data) requests (see the griddap and tabledap documentation).

Requesting Compressed Files

ERDDAP doesn't offer results stored in compressed (e.g., .zip or .gzip) files. Instead, ERDDAP looks for accept-encoding in the HTTP GET request header sent by the client. If a supported compression type ("gzip", "x-gzip", or "deflate") is found in the accept-encoding list, ERDDAP includes "content‑encoding" in the HTTP response header and compresses the data as it transmits it. It is up to the client program to look for "content-encoding" and decompress the data accordingly. Requesting compression is optional, but compressed responses are often 3-10 times faster, so this is a big time savings if you are downloading lots of large files. (Note that there is no benefit to requesting compressed .png files since the files' contents are already compressed.)

• By default, browsers and OPeNDAP clients always request compressed data and decompress the returned data.
• With curl, add --compressed to the command line to tell curl to request a compressed response and automatically decompress it.
• With other client software, you have explicitly set this up.
  Here is a Java example.
  Here is a Python example (although you should either handle deflate'd responses or not request deflate).

Access URLs for ERDDAP's Services

ERDDAP has these URL access points for computer programs:

• To get the list of the main resource access URLs, use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
   
• To get the current list of all datasets, use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
   
• To get metadata for a specific data set (the list of variables and their attributes), use
  http://erddap.digitalocean.ie/erddap/info/datasetID/index.fileType
  for example,
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
   
• To get the results of full text searches for datasets (using "searchFor=wind%20speed" as the example), use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
  (Your program or script may need to percent-encode the value in the query.)
   
  Or, use the OpenSearch 1.1 standard to do a full text search for datasets.
   
• To get the results of advanced searches for datasets (using "searchFor=wind%20speed" as the example), use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
  But experiment with Advanced Search in a browser to figure out all of the optional parameters. (Your program or script may need to percent-encode the value in the query.)
   
• To get the list of categoryAttributes (for example, institution, long_name, standard_name), use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
   
• To get the list of categories for a specific categoryAttribute (using "standard_name" as the example), use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
   
• To get the list of datasets in a specific category (using "standard_name=time" as the example), use
  .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
   
• To get the current list of all datasets available via a specific protocol,
  • For griddap: use
    .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
  • For tabledap: use
    .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
  • For WMS: use
    .csv, .htmlTable, .itx, .json, .jsonlCSV1, .jsonlCSV, .jsonlKVP, .mat, .nc, .nccsv, .tsv, or .xhtml.
     
• Griddap and tabledap have many web services that you can use.
  • The Data Access Forms are just simple web pages to generate URLs which request data (for example, satellite and buoy data). The data can be in any of several common file formats. Your program can generate these URLs directly. For more information, see the griddap documentation and tabledap documentation.
     
  • The Make A Graph pages are just simple web pages to generate URLs which request graphs of a subset of the data. The graphs can be in any of several common file formats. Your program can generate these URLs directly. For more information, see the griddap documentation and tabledap documentation.
     
  • To get a dataset's structure, including variable names and data types, use a standard OPeNDAP .dds resquest. For example,
    http://erddap.digitalocean.ie/erddap/griddap/jplMURSST41.dds (gridded data) or
    http://erddap.digitalocean.ie/erddap/tabledap/pmelTaoDySst.dds (tabular data).
     
  • To get a dataset's metadata, use a standard OPeNDAP .das resquest. For example,
    http://erddap.digitalocean.ie/erddap/griddap/jplMURSST41.das (gridded data) or
    http://erddap.digitalocean.ie/erddap/tabledap/pmelTaoDySst.das (tabular data).
     
  • ERDDAP has a special tabular dataset called allDatasets which has data about all of the datasets currently available in this ERDDAP. There is a row for each dataset. There are columns with different types of information (for example, datasetID, title, summary, institution, license, Data Access Form URL, Make A Graph URL). Because this is a tabledap dataset, you can use a tabledap data request to request specific columns and rows which match the constraints, and you can get the response in whichever response file type you prefer, for example, .html, .xhtml, .csv, .json, .jsonlCSV1, .jsonlCSV, or .jsonlKVP.
     
• ERDDAP's other protocols also have web services that you can use. See
  • ERDDAP's WMS documentation
     
• ERDDAP offers RSS subscriptions, so that your computer program can find out if a dataset has changed.
   
• ERDDAP offers email/URL subscriptions, which notify your computer program whenever a dataset changes.
   
• ERDDAP offers several converters as web pages and as web services:
  • Convert a Common Oceanic/Atmospheric Acronym to/from a Full Name
  • Convert a Common Oceanic/Atmospheric Variable Name to/from a Full Name
  • Convert a FIPS County Code to/from a County Name
  • Convert a CF Standard Name to/from a GCMD Science Keyword
  • Convert a String Time to/from a Numeric Time
  • Convert UDUNITS to/from Unified Code for Units of Measure (UCUM)
  • Convert Out-of-Date URLs into Up-to-Date URLs
     
• ERDDAP has a system to keep track of Out-Of-Date Datasets. See the Options at the bottom of that web page.
   

If you have suggestions for additional links, contact bob dot simons at noaa dot gov.

Using ERDDAP as a Data Source within Your Java Program

As described above, since Java programs can access data available on the web, you can write a Java program that accesses data from any publicly accessible ERDDAP installation.

Or, since ERDDAP is an all-open source program, you can also set up your own copy of ERDDAP on your own server (publicly accessible or not) to serve your own data. Your Java programs can get data from that copy of ERDDAP. See Set Up Your Own ERDDAP.

Log in to access private datasets.

Many ERDDAP installations don't have authentication enabled and thus don't provide any way for users to login, nor do they have any private datasets.

Some ERDDAP installations do have authentication enabled. Currently, ERDDAP only supports authentication via Google-managed email accounts, which includes email accounts at NOAA and many universities. If an ERDDAP has authentication enabled, anyone with a Google-managed email account can log in, but they will only have access to the private datasets that the ERDDAP administrator has explicitly authorized them to access. For instructions on logging into ERDDAP from a browser or via a script, see Access to Private Datasets in ERDDAP.

ERDDAP Version

If you want to use a new feature on a remote ERDDAP, you can find out if the new feature is available by sending a request to determine the ERDDAP's version number, for example,
http://erddap.digitalocean.ie/erddap/version
ERDDAP will send a text response with the ERDDAP version number of that ERDDAP. For example: ERDDAP_version=2.14
If you get an HTTP 404 Not-Found error message, treat the ERDDAP as version 1.22 or lower.

Or, you can request the version_string, which may have additional information. For example,
http://erddap.digitalocean.ie/erddap/version_string
ERDDAP will send a text response with the ERDDAP version_string of that ERDDAP. It will be a floating point number (the version number) with an optional suffix of '_' plus additional ASCII text (no spaces or control characters). For example: ERDDAP_version_string=1.82_JohnsFork
If you get an HTTP 404 Not-Found error message, treat the ERDDAP as version 1.80 or lower.

 

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ERDDAP, Version 2.14
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