An 8211 file (DDFModule) consists of a series of logical records. The first record is special, and is called the DDR (Data Description Record). It basically contains definitions of all the data objects (fields or DDFFieldDefn objects) that can occur on the following data records.
The remainder of the records are known as DRs (data records - DDFRecord). They each contain one or more field (DDFField) instances. What fields appear on what records is not defined by ISO 8211, though more specific requirements may be implied by a particular data standard such as SDTS or S-57.
Each field instance has a name, and consists of a series of subfields. A given field always has the same subfields in each field instance, and these subfields are defined in the DDR (DDFSubfieldDefn), in association with their field definition (DDFFieldDefn). A field may appear 0, 1, or many times in a DR.
Each subfield has a name, format (from the DDFSubfieldDefn) and actual subfield data for a particular DR. Some fields contain an array of their group of subfields. For instance a coordinate field may have X and Y subfields, and they may repeat many times within one coordinate field indicating a series of points.
This would be a real good place for a UML diagram of ISO 8211, and the corresponding library classes!
To establish access to an ISO 8211 dataset, instantiate a DDFModule object, and then use the DDFModule::Open() method. This will read the DDR, and establish all the DDFFieldDefn, and DDFSubfieldDefn objects which can be queried off the DDFModule.
The use DDFModule::ReadRecord() to fetch data records (DDFRecord). When a record is read, a list of field objects (DDFField) on that record are created. They can be queried with various DDFRecord methods.
Data pointers for individual subfields of a DDFField can be fetched with DDFField::GetSubfieldData(). The interpreted value can then be extracted with the appropriate one of DDFSubfieldDefn::ExtractIntValue(), DDFSubfieldDefn::ExtractStringValue(), or DDFSubfieldDefn::ExtractFloatValue(). Note that there is no object instantiated for individual subfields of a DDFField. Instead the application extracts a pointer to the subfields raw data, and then uses the DDFSubfieldDefn for that subfield to extract a usable value from the raw data.
Once the end of the file has been encountered (DDFModule::ReadRecord() returns NULL), the DDFModule should be deleted, which will close the file, and cleanup all records, definitions and related objects.
The precise license text is:
Copyright (c) 1999, Frank Warmerdam
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% unzip iso8211lib-1.4.zip
I would like to thank:
*/ /*! \page ISO8211_Example \include 8211view.cpp */