Easier access to scientific data
Brought to you by NOAA NMFS SWFSC ERD
|
ERDDAP
Easier access to scientific data |
Brought to you by NOAA NMFS SWFSC ERD |
– a web page with a form that humans with browsers can use
(in this case, to get data, graphs, or information about datasets).
– a URL that computer programs can use
(in this case, to get data, graphs, and information about datasets).
.
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 textfield of your browser (for example,
http://bmlsc.ucdavis.edu:8080/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
and
Resource Oriented Architecture (ROA).
and
AJAX applications.
,
as is ERDDAP, which makes the system simpler.
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://bmlsc.ucdavis.edu:8080/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
web sites that percent encode/decode for you.
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.
Browsers and OPeNDAP clients do this by default. They request compressed data and
decompress the returned data automatically.
Other clients (e.g., Java programs) have to do this explicitly.
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:
)
)
)
or
ERDDAP-specific info)
)
)
)
)
)
)
)
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
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).
Access URLs for ERDDAP's Services
ERDDAP has these URL access points for computer programs:
the value in the query.)
the value in the query.)
resquest. For example,
resquest.
For example,
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.
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.
Or, you can request the version_string, which may have additional information.
For example,
http://bmlsc.ucdavis.edu:8080/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.