griddist_zonal - ObjectVision/GeoDMS GitHub Wiki

Grid functions griddist_zonal

The griddist_zonal function calculates grid-based distances with additional impedance penalties when crossing zone boundaries.

griddist_zonal(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster, zoneGrid: raster->UInt16, zoneBarrier: Float)
griddist_zonal(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster, zoneGrid: raster->UInt16, zoneBarrier: Float, startvalues: pointset->Float)

Additional variants:

• griddist_zonal_maximp - with maximum impedance cutoff
• griddist_zonal_untiled - non-tiled variant
• griddist_zonal_latitude_specific - accounts for latitude-dependent cell sizes
• Combinations of the above suffixes

Similar to Griddist, but with additional zonal boundary handling. When the shortest path crosses from one zone to another (cells with different zoneGrid values), an extra impedance penalty (zoneBarrier) is added.

The algorithm uses Dijkstra's shortest path algorithm with zone boundary checking. Complexity is O(n × log n) where n is the number of grid cells.

The zone boundary check adds minimal overhead as it only compares adjacent cell zone values during path expansion.

• impedanceGrid values must be non-negative
• zoneBarrier must be non-negative
• Value types of impedanceGrid, zoneBarrier, and startvalues must be compatible Float types

• Transportation modeling where crossing administrative boundaries incurs extra costs
• Ecological modeling where habitat patches have different traversal resistance
• Market analysis where service areas span multiple jurisdictions

attribute<Float64> travel_time (GridDomain) := griddist_zonal(
    travel_cost,
    destination/GridDomain_rel,
    municipality_grid,
    60.0  // 60 seconds penalty at municipal boundaries
);

• Griddist
• griddist_maximp
• Grid functions
• Impedance functions

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