Every CCOGIF file may contain one or more datasets.1The FME’s CCOGIF writer currently supports only a single dataset.The first record of each dataset in a CCOGIF volume is called the Data Set Header Record (DSHR). It provides information particular to the dataset not only for the human user—it also directs computer applications on how to process the data.
The portions of theDSHRthat relate to the processing of the data are of specific interest to the CCOGIF writer. When it writes out data within a dataset, it must remain consistent with the dataset characteristics set out in theDSHR. The following information is particularly interesting to the writing process.
- Coordinate data type: TheDSHRspecifies the data type,INT,REALorDMS, for each of the x, y, and z coordinate values within the dataset. The CCOGIF writer uses the values of theDSHRmetadata feature’sccogif_x_data_type,ccogif_y_data_type, andccogif_z_data_typeattributes to format the numerical coordinates correctly.
- Data set content indicator: The Data Set Content Indicator (DSCI) is a subrecord of theDSHRthat tells whether data is 3D, whether there is a known point in each area, and whether various topology information such as, point to line topology, line to point topology, line collocation, line to area topology, and area to line topology, is present in the entity attributes. FME’s CCOGIF writer currently does not generate any topology information, however it passes along any that has been added to geometric entity features which have been given to it.
- Coordinate system and map projection: The correct coordinate system for the output CCOGIF dataset must be specified in aDSHRmetadata feature, as this information is not yet tied in to FME’s coordinate system manager. If no coordinate system information is provided to the CCOGIF writer, it will arbitrarily choose a Universal Transverse Mercator (UTM) zone 18 projection, which is most likely not what is wanted.
The following table lists the default values for all attributes in theDSHR. These default values will be written out for any attributes not mentioned in “any”DSHRmetadata feature given to the writer.
Attribute Name |
Contents – Default Value |
ccogif_data_set_name |
FME-generated CCOGIF dataset |
ccogif_ds_cre_date |
Current date |
ccogif_ds_loc_text |
Empty string (“ ”) |
ccogif_related_ds |
Empty string (“ ”) |
ccogif_data_three_dim |
Depends on whether first entity feature written is two- or three-dimensional. |
ccogif_pt_to_ln_topo |
Ffor False |
ccogif_ln_to_pt_topo |
Ffor False |
ccogif_colloc_exists |
Ffor False |
ccogif_ln_to_area_topo |
Ffor False |
ccogif_area_to_ln_topo |
Tfor True |
ccogif_known_pt_in_area |
Tfor True |
ccogif_attrs_in_entity |
Tfor True |
ccogif_feat_classes |
Empty string (“ ”) |
ccogif_num_data_grp |
Number of data groups written to this CCOGIF dataset. |
ccogif_num_ufl_recs |
Computed from the amount of user data specified on theUFLRmetadata records. |
ccogif_num_emd_recs |
Number ofEMDRs to write to the dataset. |
ccogif_x_data_type, |
REAL |
ccogif_x_data_units, |
METRESfor x and y, |
ccogif_z_min_value, |
If the entity data is 3D, these are the actual minimum and maximum elevations. Otherwise, they are left blank. |
ccogif_proj_id |
Defaults to UTM zone 18, so the projection ID will be Transverse Mercator (0200) |
ccogif_geod_datum |
名字的大地基准 |
ccogif_adj_name |
Name of adjustment |
ccogif_vert_datum |
Name of vertical datum |
Theccogif_num_ufl_recsattribute on theDSHRis completely dependent on the amount of user data passed to the CCOGIF writer inUFLRmetadata features and is always overwritten by the writer.
The FME defaults to a map projection of UTM zone 18. The following table presents the default values for the projection-related attributes for theDSHR.
Attribute Name |
Content – Default Value |
ccogif_proj_id |
Constant:0200 |
ccogif_proj_name |
Constant:TRANSVERSE MERCATOR |
ccogif_proj_cent_merid |
Constant:75 |
ccogif_proj_zone_width |
Constant:6 |
ccogif_proj_sphd_name |
GRS 80 |
ccogif_proj_semi_major |
Constant:6.378137E+06 |
ccogif_proj_semi_minor |
Constant:6.35675231E+06 |
ccogif_proj_eccent |
Constant:6.694380070E-03 |
ccogif_proj_scl_fact |
Constant:0.9996 |
ccogif_proj_false_east, ccogif_proj_fals_north |
Constant:500000 east, 0 north |
ccogif_proj_zone |
Constant:18 |
ccogif_proj_orig_east, |
Constant:(0,0) |
ccogif_proj_num_bnd_crd |
Constant:0 |
ccogif_proj_bnd_crd{n}.x, |
Empty string (“ ”) |
It is important to note that the CCOGIF writer requires theDSHRinformation (especially the x,y, and z data types) before it starts to write entity data to the CCOGIF file.