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<title>IHO S-57 (ENC)</title>
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<h1>IHO S-57 (ENC)</h1>
IHO S-57 datasets are supported for read access.<p>
The S-57 driver module produces features for all S-57 features in one
or more related S-57 data files. An S-57 dataset can be a directory (in
which case all S-57 files in the directory are selected), an S-57 catalog
file (in which case all files referred to from the catalog are selected)
or an individual S-57 data file. <p>
S-57 feature objects are translated into features. S-57 geometry
objects are automatically collected and formed into geometries on the
features.<P>
The S-57 reader depends on having two supporting files, s57objectclasses.csv,
and s57attributes.csv available at runtime in order to translate features
in an object class specific manner. These should be in the directory pointed
to by the environment variable S57_CSV, or in the current working directory.
<p>
S-57 update files contain information on how to update a distributed S-57
base data file. The base files normally have the extension .000 while the
update files have extensions like .001, .002 and so on. The S-57 reader
will normally read and apply all updates files to the in memory version of
the base file on the fly. The feature data provided to the application
therefore includes all the updates. <p>
<h3>Feature Translation</h3>
Normally all features read from S-57 are assigned to a layer based on
the name of the object class (OBJL) to which they belong. For instance,
with an OBJL value of 2, the feature is an "Airport / airfield" and has
a short name of "AIRARE" which is used as the layer name. A typical
S-57 transfer will have in excess of 100 layers.<p>
Each feature type has a predefined set of attributes as defined by the
S-57 standard. For instance, the airport (AIRARE) object class can
have the AIRARE, CATAIR, CONDTN, CONVIS, NOBJNM, OBJNAM, STATUS, INFORM,
NINFOM, NTXTDS, PICREP, SCAMAX, SCAMIN, TXTDSC, ,RECDAT, RECIND, SORDAT,
and SORIND attributes. These short names can be related to longer, more
meaningful names using an S-57 object/attribute catalog such as the
S-57 standard document itself, or the catalog files (s57attributes.csv,
and s57objectclasses.csv).
Such a catalog can also be used to establish all the available object classes,
and their attributes.<p>
The following are some common attributes, including generic attributes
which appear on all feature, regardless of object class.
is turned on. <p>
<pre>
Attribute Name Description Defined On
-------------- ----------- ----------
GRUP Group number. All features
OBJL Object label code. This number All features
indicates the object class of the
feature.
RVER Record version.
AGEN Numeric agency code, such as 50 for All features
the Canadian Hydrographic Service.
A potentially outdated list is
available in agencode.txt.
FIDN Feature identification number. All features
FIDS Feature identification subdivision. All features
DSNM Dataset name. The name of the file All features
the feature came from. Used with
LNAM to form a unique dataset wide
identifier for a feature.
INFORM Informational text. Some features
NINFOM Informational text in national Some features
language.
OBJNAM Object name Some features
NOBJNM Object name in national Some features
language.
SCAMAX Maximum scale for display Some features
SCAMIN Minimum scale for display Some features
SORDAT Source date Some features
</pre>
The following are present if LNAM_REFS is enabled:
<pre>
LNAM Long name. An encoding of AGEN, All features
FIDN and FIDS used to uniquely
identify this features within an
S-57 file.
LNAM_REFS List of long names of related features All Features
FFPT_RIND Relationship indicators for each of All Features
the LNAM_REFS relationships.
</pre>
<h3>Soundings</h3>
Depth soundings are handled somewhat specially in S-57 format, in order
to efficiently represent the many available data points. In S-57 one
sounding feature can have many sounding points. The S-57 reader
splits each of these out into it's own feature type `SOUNDG' feature
with an s57_type of `s57_point3d'. All the soundings from a single
feature record will have the same AGEN, FIDN, FIDS and LNAM value.<p>
<h3>S57 Control Options</h3>
There are several control options which can be used to alter the behavior of
the S-57 reader. Users can set these by appending them in the
OGR_S57_OPTIONS environment variable.
<ul>
<li> <b>UPDATES</b>=APPLY/IGNORE: Should update files be incorporated into the
base data on the fly. Default is APPLY.<p>
<li> <b>SPLIT_MULITPOINT</b>=ON/OFF: Should multipoint soundings be split
into many single point sounding features. Multipoint geometries are not well
handle by many formats, so it can be convenient to split single sounding features with many points into many single point features. Default is OFF. <p>
<li> <b>ADD_SOUNDG_DEPTH</b>=ON/OFF: Should a DEPTH attribute be added on
SOUNDG features and assign the depth of the sounding. This should only be
enabled with SPLIT_MULTIPOINT is also enabled.
Default is OFF. <p>
<li> <b>RETURN_PRIMITIVES</b>=ON/OFF: Should all the low level geometry
primitives be returned as special IsolatedNode, ConnectedNode, Edge and
Face layers. Default is OFF. <p>
<li> <b>PRESERVE_EMPTY_NUMBERS</b>=ON/OFF: If enabled, numeric attributes
assigned an empty string as a value will be preserved as a special numeric
value. This option should not generally be needed, but may be useful
when translated S-57 to S-57 losslessly. Default is OFF. <p>
<li> <b>LNAM_REFS</b>=ON/OFF: Should LNAM and LNAM_REFS fields be
attached to features capturing the feature to feature relationships in the
FFPT group of the S-57 file. Default is OFF.<p>
<li> <b>RETURN_LINKAGES</b>=ON/OFF: Should additional attributes
relating features to their underlying geometric primtives be attached. These
are the values of the FSPT group, and are primarily needed when doing
S-57 to S-57 translations. Default is OFF.<p>
</ul>
Example:
<pre>
set OGR_S57_OPTIONS = "RETURN_PRIMITIVES=ON,RETURN_LINKAGES=ON,LNAM_REFS=ON"
</pre>
<h3>S-57 Export</h3>
Preliminary S-57 export capability has been added in GDAL/OGR 1.2.0 but
is intended only for specialized use, and is not properly documented at
this time. Setting the following options is a minimum required to
support S-57 to S-57 conversion via OGR.<p>
<pre>
set OGR_S57_OPTIONS = "RETURN_PRIMITIVES=ON,RETURN_LINKAGES=ON,LNAM_REFS=ON"
</pre>
<h3>See Also</h3>
<ul>
<li> <a href="http://www.s-57.com/">S-57 Online Object/Attribute Catalog</a>
<li> <a href="http://home.gdal.org/projects/s57/index.html">Frank's S-57
Page</a>: Links to other resources, and sample datasts.<p>
</ul>
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