In CCOGIF files, geometric entities are grouped by geographic area, then further grouped according to attributes of the data itself such as, data themes with common geometric entity types and sets of attributes. This is very different from the conceptual divisions between data entities that typically must rely on the content of the primary feature code to provide notion similar to FME’s feature types. The interpretation of a feature type requires knowledge of the conventions by which the data was encoded in the CCOGIF file.
Tip: Tip: Geomatics Canada’s document titled “Conversion of NTDB Data into CCOGIF Format” provides an example of such a set of convention.
Without knowledge of the underlying conventions, it is very difficult to automatically generate a single mapping file that works with more than one input file. The definitions of the themes within the groups just isn’t consistent enough.
To overcome this obstacle, FME can generate two different kinds of mapping files:
- The first is a generic mapping file that extracts all of the information it can from the features, then groups them into FME feature types based on the data theme and data group. When run, this mapping file provides a very simple representation of the data in the output format without regard to any specific set of conventions.
- The second type of mapping file which may be generated takes into account the representation of the National Topographic Data Base (NTDB) data in the CCOGIF file and is referred to as a profile-specific mapping file.
The term profile is used to refer to a set of file, feature, and attribute naming conventions used to store NTDB in another, that is non-CCOGIF, format. Geomatics Canada has three such profiles, each designed to embody NTDB data within the characteristics and limitations of a particular file format. The three profiles are for ASCII Ungenerate (ARCGEN), MIF/MID, and DXF. The FME provides a way to generate mapping files to write CCOGIF data in another format, generally following the conventions of any of these profiles.
Note: The target format does not have to be the same as the format for which the profile was defined.
The resulting files do not exactly conform to the profile, due to differences in data format and to the way in which mapping file generation works within FME. However, the resulting data files are generally much closer to what you would want than those that a generic mapping file would yield. Manual editing of the mapping files can, of course, bring it much closer.
The advantage of the profile-specific mapping files is that the knowledge of the conventions for storing the NTDB in the source and destination formats is stored in the mapping file. Therefore a single mapping file may be used for a whole series of mapsheets, whereas a generic mapping file would only be applicable to a single CCOGIF file.
The disadvantage to the profile-specific mapping file is that the actual generation process needs a few parameters about the input mapsheets. This requires some knowledge of the data in order to generate the mapping file. In addition, the generated mapping file must be used with NTDB data that is consistent with the parameters with which the mapping file was generated.
The following sections describe the process and application of the two kinds of mapping files in greater detail.