Impedance functions

network-functions Impedance functions

There are four impedance functions:

  • impedance_table(…): when all given startPoints have to be considered as a single origin zone, resulting in:
    • an attribute DstZone->Impedance with the lowest route Impedance per destination zone.
    • optional attributes as sub-items depending on the used options.
    • so the result is a table with for each origin the impedance to the nearest destination.
  • impedance_matrix(…) when startPoints can relate to multiple origin zones, resulting in
    • a unit<uint32> reflecting the set of all or all found od-pairs
    • optional attributes as sub-items depending on the used options.
  • impedance_matrix_od64(…), similar to impedance_matrix_od(…), but resulting in a unit<uint64> in order to accommodate more than $2^{32} − 2$ od-pairs.
  • griddist using an implied network between neighbouring raster cell centers to do something similar to impedance_table(…) with less effort.

All these operations require at least the following four arguments:

  • options : {∅} → String, a String parameter indicating function options, described below.
  • impedance : Link → Impedance, a Measure (Float32 or Float64) attribute of Links with the Impedance per Link.
  • f1 : Link → Node, a Node attribute of Link indicating the from node of each link.
  • f2 : Link → Node, a Node attribute of Link indicating the to node of each link.

Note that Impedance functions can run different OrgZones in parallel, up to the number of cores of the running machine, as their tree growth is independent. This does not affect impedance_table, as that only grows one tree.

phased out variants

  • dijkstra_s(…) to be replaced by impedance_table(…)
  • dijkstra_m(…) to be replaced by impedance_matrix(…)
  • dijkstra_m64(…) to be replaced by impedance_matrix_od64(…)

see also