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<html><head><title>IHO S-57 (ENC)</title></head><body bgcolor="#ffffff"><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 oneor more related S-57 data files. An S-57 dataset can be a directory (inwhich case all S-57 files in the directory are selected), an S-57 catalogfile (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 geometryobjects 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 featuresin an object class specific manner. These should be in the directory pointedto by the encironment 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 theupdate 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 ofthe 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 onthe 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 hasa short name of "AIRARE" which is used as the layer name. A typicalS-57 transfer will have in excess of 100 layers.<p>Each feature type has a predefined set of attributes as defined by theS-57 standard. For instance, the airport (AIRARE) object class canhave 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, moremeaningful names using an S-57 object/attribute catalog such as theS-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 orderto efficiently represent the many available data points. In S-57 onesounding feature can have many sounding points. The S-57 readersplits each of these out into it's own feature type `SOUNDG' featurewith an s57_type of `s57_point3d'. All the soundings from a singlefeature 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 ofthe 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 thebase data on the fly. Default is APPLY.<p><li> <b>SPLIT_MULITPOINT</b>=ON/OFF: Should multipoint soundings be splitinto many single point sounding features. Multipoint geometries are not wellhandle 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 onSOUNDG features and assign the depth of the sounding. This should only beenabled 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 andFace layers. Default is OFF. <p><li> <b>PRESERVE_EMPTY_NUMBERS</b>=ON/OFF: If enabled, numeric attributesassigned an empty string as a value will be preserved as a special numericvalue. 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 theFFPT 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. Theseare 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 butis intended only for specialized use, and is not properly documented atthis 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://home.gdal.org/projects/s57/index.html">Frank's S-57Page</a>: Links to other resources, and sample datasts.<p></ul></body></html>⌨️ 快捷键说明
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