14
Copyright © 2016 Open Geospatial Consortium
obviously, plus BSR, HGT, and MODT and 5 others remain optional AO1, BBH, BBL, BBW, and SCALn.
6.2.2 Generation of HGT
The HGT attribute represents a special case because table 5-47 suggests that the attribute is optional while, in fact, it should always be present. If you carefully read its description
in paragraph 5.3.1.2.3.17, you realize that HGT is required in both the line and figure point features of the Powerline Network.
For line features, HGT represents the average height above ground of the powerline when no MODL is specified, as suggested by the discussion about HGT in section 5.3.1.17 of
the CDB Standard Volume 1: OGC CDB Core Standard: Model and Physical Data Store Structure In the figure point features, HGT represents the height above ground of the
pylon, whether or not a MODL is provided. In either file, when MODL is supplied, HGT represents the height of the 3D model above the ground.
You should read guideline 6.3 – old Annex 6.3 for a complete discussion about HGT
6.2.3 Pylon Orientation
If the orientation of the pylon is specified by AO1, then use the value as-is. If the orientation is not specified, the client device must compute its value using the orientation
of the segments of the line that are adjacent to the pylon. In the case of the first and last segments, the orientation of the segment is also the orientation of the pylon. For the other
segments, the orientation of the pylon is the average of the orientation of the two adjacent segments.
6.2.4 Number of Wires
When no MODL is provided at all – meaning no MODL for the line and none for the figure points – and because there is no attribute specifying the number of wires along the
transmission line, the client device must assume a generic powerline with two wires separated by a width of WGP meters connecting generic posts simple pylons of HGT
meters high.
When a common MODL is specified for the whole line and no figure points are provided, it is possible to determine the number of wires by counting the number of attach points in
the 3D model. Refer to guideline 6.1.2 old 6.1.2 for details on how to detect attach points.
If specific MODLs are defined through figure points, the number of attach points in each 3D model of the collection of all MODLs referenced by the powerline network must be
identical. For instance, if the line refers to a generic pylon supporting 4 wires, then all specific pylons referenced as figure points must also support 4 wires. Furthermore, the
general configuration of all pylons must be identical. If the general pylon supports 6 wires configured as a matrix of 2 wires horizontally by 3 wires vertically, then all specific
pylons must also share the same configuration.
15
Copyright © 2016 Open Geospatial Consortium
6.2.5 How to Connect Wires to Attach Points
