VPF Tile Topology (Coverage)
Summary
Creates cross-tile topology for all tiled coverages in a Vector Product Format (VPF) database library, or topology for an individual tile in a VPF library.
This tool is used for postprocessing a VPF coverage or library from Export to VPF output. For efficiency purposes, it's recommended that you build cross-tile topology only after you have finished converting all coverages in your VPF library.
Usage
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Military Standard MIL-STD-2407 (June 28, 1996) refines the definition of cross-tile topology. The VPF Tile Topology command has been updated to meet the new specification. You may use the optional parameter to choose the 93 or 96 VPF Standard.
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VPF Tile Topology works on all tiled coverages of a VPF library or a single coverage within that library. The last optional parameter, VPF_cover, allows you to select a particular coverage in which cross-tile topology should be populated. It is more efficient, however, to implement VPF Tile Topology after all coverages for a library have been converted from the VPF format.
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VPF Tile Topology using the 1993 VPF Standard does not handle the situation where more than two edges coincide along a tile boundary. It is impossible for VPF Tile Topology to know how to assign left-face and right-face values to each edge.
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The 1996 VPF Standard requires that cross-tile topology be implemented on the connected nodes. For cross-tile to work correctly, the "first_edge" column in the connected node tables must be a Triplet type.
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Since VPF Tile Topology makes modifications to the primitive file in your VPF database, it is important to understand the requirements of the VPF data before the cross-tile process can occur correctly. The most important things to remember about creating 1996 cross-tile topology are the following:
- If an edge touches a tile boundary, the point at which it touches must be a node.
- All nodes that exist on a tile boundary must exist in the adjacent tile if such tile exists.
- All edges that are coincident with an interior tile must exist in both tiles.
- All tile boundary edges must be totally straight edges.
Syntax
| Parameter | Explanation | Data Type |
VPF_library |
Location of the VPF database library for which cross-tile topology is to be created. | Folder |
sig_digits (Optional) |
The number of digits the software will use when trying to match node coordinates at tile boundaries. The larger the number, the smaller the search tolerance. The default value is 4. | Long |
VPF_standard (Optional) |
The VPF Standard to be used. The VPF Standard has two ways of defining cross-tile topology.
| Long |
spec_cover (Optional) |
Specifies whether to process all the coverages in the VPF library or only the specified coverage.
| String |
Code Sample
The following stand-alone script demonstrates how to export two coverages to VPF and then create cross-tile topology for the VPF covereages.
# Name: VPFTile_Example.py
# Description: Exports two coverages to VPF format then builds tile topology
# Requirements: ArcInfo Workstation
# Import system modules
import arcpy
from arcpy import env
# Set environment settings
env.workspace = "C:/data"
# Set local variables
inCover1 = "coastb"
inCover2 = "coastc"
outFile1 = "C:/output/vpfdb/wlib/coast2"
outFile2 = "C:/output/vpfdb/wlib/coast3"
vpfLibrary = "C:/output/vpfdb"
vpfStandard = 96
specCover = "ALL"
# Execute VPFExport
arcpy.VPFExport_arc(inCover1, outFile1)
arcpy.VPFExport_arc(inCover2, outFile2)
# Execute VPFTile
arcpy.VPFTile_arc(vpfLibrary, "", vpfStandard, specCover)