griddist_latitude_specific - ObjectVision/GeoDMS GitHub Wiki
Grid functions griddist_latitude_specific
The griddist_latitude_specific function calculates grid-based distances accounting for latitude-dependent cell sizes on geographic (lat/long) grids.
griddist_latitude_specific(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster)
griddist_latitude_specific(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster, startvalues: pointset->Float)
Additional variants with combined suffixes:
- griddist_maximp_latitude_specific - with maximum impedance cutoff
- griddist_untiled_latitude_specific - non-tiled variant
- griddist_maximp_untiled_latitude_specific - combination
- griddist_zonal_latitude_specific - with zone boundary penalties
- griddist_zonal_maximp_latitude_specific - with both zone penalties and max impedance
Similar to Griddist, but with latitude-dependent distance factors. On geographic coordinate grids (lat/long), cell sizes vary with latitude:
- At the equator, longitude degrees represent the maximum distance
- At higher latitudes, longitude degrees represent smaller physical distances
- Latitude degrees represent consistent distances
This function automatically calculates appropriate distance factors based on row position.
| argument | description | type |
|---|---|---|
| impedanceGrid | Impedance value for each cell (non-negative) | raster->Float |
| pointset_raster_rel | Relation from points to raster cells | pointset->raster |
| startvalues | (optional) Initial impedance values at start points | pointset->Float |
The algorithm uses Dijkstra's shortest path algorithm with latitude-adjusted distance calculations. Complexity is O(n × log n) where n is the number of grid cells.
The latitude factor computation adds minimal overhead as factors are precomputed per row.
- impedanceGrid values must be non-negative
- The grid should use geographic (lat/long) coordinates for meaningful results
- Value types of impedanceGrid and startvalues must be compatible Float types
- Global or continental-scale accessibility modeling
- Analysis on geographic coordinate grids where metric accuracy matters
- Climate and environmental modeling on lat/long grids
// Grid in WGS84 lat/long coordinates
attribute<Float64> travel_time (GlobalGrid) := griddist_latitude_specific(
travel_cost,
destination/GlobalGrid_rel
);
5.85