syntax

• griddist(impedance, destpoint_gridid, startvalues)

definition

griddist(impedance, destpoint_gridid, startvalues) results in a travel impedance value for each cell of a grid towards the nearest point in a point set, taking into account the impedance of each grid cell (e.g. based on slope or land use type). The function has the following arguments:

• impedance is a grid attribute containing a resistance value for each cell.
• destpoint_gridid contains a set of grid index numbers for the pointset to which the impedances are calculated. See RelateToGrid for how to calculate such a grid relation attribute
• startvalues contains the initial impedance values for the point set.

The impedance is calculated taken into account the length of each cell (with value 1 for each cell) and the grid cell impedance. The resulting values unit has a float32 or float64 value type, based on the value type of the impedance and startvalues arguments. The resulting domain unit is the domain unit of the impedance argument.

description

The griddist function is often used to calculate off road travel resistances, where e.g. the land use type and the slope have an important influence on the travel time/costs.

conditions

The values unit of the arguments impedance and startvalues must match.

The domain of the arguments destpoint_gridid and startvalues must match.

5.85

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 1.5 2 0 1.5 1 0
GridDomain, nr of rows = 5, nr of cols = 5

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