The VPF Tile Topology tool provides two options, one for each version of the Vector Product Format (VPF) standard:
- For the 1993 version, VPF Tile Topology does not handle the situation where more than two edges coincide along a tile boundary. It is impossible to assign left-face and right-face values to each edge.
- For the 1996 version, cross-tile topology must be created on the connected nodes. For cross-tile to work correctly, the first_edge column in the connected node tables must be a Triplet type.
Military Standard MIL-STD-2407 (1993 and June 28, 1996) specifies details on VPF tile topology. The 1996 version refines the definition of cross-tile topology as described in the 1993 version.
The VPF Military Standard requires that primitives, such as edges and faces between tiles, are connected. The Export To VPF tool converts coverage data one tile at a time. Once all tiled data has been converted, the VPF Tile Topology tool is used to build cross-tile topology.
The edge table for a tiled VPF coverage contains right_edge and left_edge columns that are defined as triplet ID data types. If the coverage also contains faces, the edge table will have triplet ID right_face and left_face columns. The first section of a triplet ID column is for internal topological relationships. It contains an identifier that links one primitive to another primitive within one tile. The second and third sections of a triplet ID column are for external (cross-tile) topological relationships. The second element holds an identifier to an adjoining tile, and the third element stores an identifier to a connecting primitive in that adjoining tile.
When a VPF coverage is converted with the Export To VPF tool, the second and third values in the triplet ID columns in the edge tables are initialized to zero. The VPF Tile Topology tool updates these values if a connecting primitive was found in the adjoining tiles.
The 1996 Standard introduces cross-tile topology on the connected node table. Any node that occurs on a tile boundary will have a triplet ID populated with an internal first_edge and an external first_edge that occurs in the adjoining tile.Feedback on this topic?