从 osmar 对象创建的 igraph 路由对象的权重函数的基础是什么？

Question

我想知道从 osmar 对象创建 igraph 路由对象时如何计算权重值？有上限吗？

library(osmar)
library(igraph)
src <- osmsource_api(url = "https://api.openstreetmap.org/api/0.6/")
muc_bbox <- center_bbox(11.575278, 48.137222, 1000, 1000)
muc <- get_osm(muc_bbox, src)

hways <- subset(muc, way_ids = find(muc, way(tags(k == "highway"))))
hways <- find(hways, way(tags(k == "name")))
hways <- find_down(muc, way(hways))
hways <- subset(muc, ids = hways)

id<-find(muc, node(tags(v %agrep% "Sendlinger Tor")))[1]
hway_start_node <-find_nearest_node(muc, id, way(tags(k == "highway"))) 
hway_start <- subset(muc, node(hway_start_node))

id <- find(muc, node(attrs(lon > 11.58 & lat > 48.15)))[1]
hway_end_node <- find_nearest_node(muc, id, way(tags(k == "highway")))
hway_end <- subset(muc, node(hway_end_node))

### Create street graph ----
gr <- as.undirected(as_igraph(hways))

### Compute shortest route: ----
# Calculate route
route <- function(start_node,end_node) {
get.shortest.paths(gr,
                     from = as.character(start_node),
                     to = as.character(end_node), 
                     mode = "all")[[1]][[1]]}
#get Weight value
r <- route(hway_start_node,hway_end_node)
max(E(gr)[r]$weight)

谢谢！最好的问候。

Answer 1

对于大多数边，权重只是边节点之间的距离（以米为单位）：

# Get nodes Latitude & Longitude
nodes.coords <- hways$nodes$attrs[, c("lon", "lat")]
nodes.coords$id<- as.character(hways$nodes$attrs$id)
setDT(nodes.coords)

# Put two Nodes from an Edge together
edges_data_frame <- get.data.frame(gr, what = "edges")
datafrom <- nodes.coords[edges_data_frame,on = .(id = from)][,.(lonfrom = lon,latfrom=lat,weight,id,to)]
datafromto <- nodes.coords[datafrom,on = .(id = to)][,.(lonfrom, latfrom,lonto = lon,latto=lat,weight)]

# Calculate distance between nodes
datafromto[,dist:=geosphere::distHaversine(cbind(lonfrom,latfrom),cbind(lonto,latto))]

# Check percentage of Weights different of distance
nrow( datafromto[weight!=dist]) / nrow(datafromto)

[1] 0.03979914

此结果表明，对于 96% 的边，权重 = 节点之间的距离。
我不知道为什么剩下的 4% 不是这样。

从 osmar 对象创建的 igraph 路由对象的权重函数的基础是什么？

What is the basis for the weight function of igraph route object created from osmar object?

r

igraph

openstreetmap

osmar