Griddist

grid-functions griddist

The griddist is a collection of functions, used to calculate the distances in a grid.

The basic variant is the griddist(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster. Multiple variants are available, see the syntax topic.

syntax

  • griddist(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster)
  • griddist_maximp(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster, maxImp: Float)
  • griddist_zonal(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster, zoneGrid: raster->UInt16, zoneBarrier: Float)
  • griddist_zonal_maximp(impedanceGrid: raster->Float, pointset_raster_rel: pointset->raster, zoneGrid: raster->UInt16, zoneBarrier: Float, maxImp: Float)

Where each variant:

  • can have an optional additional argument startvalues: pointset->Float
  • can be suffixed by _untiled and/or
  • can be suffixed by _latitude_specific, in that order.

definition

griddist(impedanceGrid, pointset_raster_rel, startvalues) results in an impedance value for each cell of grid which is the lowest sum of impedances of paths towards any point in the pointset.

The function can have the following arguments:

  • impedanceGrid: raster->nonnegative values, an attribute of a grid-domain with an impedance for each cell (e.g. based on slope and/or land use type);
  • pointset_raster_rel: pointset->raster, a relation from a pointset to the raster domain. The pointset contains the locations, from which impedances are calculated. See point-2-grid for how to configure such a relation.
  • zonalGrid
  • boundaryImp
  • maxImp
  • startvalues: pointset->nonnegative values, the initial impedance values for the point set; can be const(0.0, pointset)

The resulting values-unit of the impedance item has a float32 or float64 value-type, based on the value type of the impedance, startvalues, boundaryImp, and/or maxImp arguments.

The resulting domain-unit is the domain unit of the impedance argument.

description

The griddist function is often used to calculate off-road or future accessibility, where e.g. geophysical factors are assumed to be important factors for assessing accessibility.

conditions

  • The values unit of the arguments impedance and startvalues must match.
  • The domain unit of the arguments pointset_raster_rel and startvalues must match.
  • the values of the first and third argument cannot be negative.

See also

impedance-functions

since version

5.85

not yet implemented

  • an aspect ratio is required to make griddist useful on a non-square rectangular raster
  • a row specific aspect ratio is required to make griddist useful on a lat-long raster
  • a cell-specific (2x2) metric is required to make griddist useful on a generic projection

example 

attribute<GridDomain> GridDomain_rel (destination);
attribute<float64>    griddist       (GridDomain) := griddist(resistance, GridDomain_rel, const(0.0, destination));

resistance

         
1 1 1 1 1
2 3 0 0 1
2 4 5 1 1
5 6 3 2 2
2 2 1 1 1

GridDomain, nr of rows = 5, nr of cols = 5

GridDomain_rel
{1, 1}
{1, 3}
{4, 1}
{4, 4}

domain destination, nr of rows = 4

griddist

         
1.71 0.71 0.50 0.50 0.71
2.50 0 0 0 0.50
3.54 2.83 2.50 0.50 0.71
4.95 4 3.33 2 0.71
2 0 1.50 1 0

GridDomain, nr of rows = 5, nr of cols = 5