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I was wondering how to convert an osmar object (an OSM relation) to a closed polygon by merging its 'outer' ways. The relation I want to fetch is the following: http://www.openstreetmap.org/relation/416271.

library(osmar)
wv <- get_osm(relation(416271), full=T)
wv
osmar object
4337 nodes, 138 ways, 9 relations

str(wv)
List of 3
 $ nodes    :List of 2
  ..$ attrs:'data.frame':   4337 obs. of  9 variables:
  .. ..$ id       : num [1:4337] 22290863 22290866 22290869 22290872 22290875 ...
  .. ..$ visible  : Factor w/ 1 level "true": 1 1 1 1 1 1 1 1 1 1 ...
  .. ..$ timestamp: POSIXlt[1:4337], format: "2006-12-30 15:22:45" "2006-12-30 15:22:45" "2006-12-30 15:22:45" ...
  .. ..$ version  : num [1:4337] 1 1 1 1 1 1 1 1 1 1 ...
  .. ..$ changeset: num [1:4337] 175959 175959 175959 175959 175959 ...
  .. ..$ user     : Factor w/ 69 levels "3dShapes","AtonX",..: 63 63 63 63 63 63 63 63 63 63 ...
  .. ..$ uid      : Factor w/ 69 levels "10613","107257",..: 45 45 45 45 45 45 45 45 45 45 ...
  .. ..$ lat      : num [1:4337] 51.4 51.4 51.4 51.4 51.4 ...
  .. ..$ lon      : num [1:4337] 3.35 3.35 3.34 3.34 3.34 ...
  ..$ tags :'data.frame':   575 obs. of  3 variables:
  .. ..$ id: num [1:575] 22290863 22290863 22290866 22290866 22290869 ...
  .. ..$ k : Factor w/ 43 levels "addr:postcode",..: 2 39 2 39 2 39 2 39 2 39 ...
  .. ..$ v : Factor w/ 40 levels "1","117639","1819",..: 9 32 9 32 9 32 9 32 9 32 ...
  ..- attr(*, "class")= chr [1:3] "nodes" "osmar_element" "list"
 $ ways     :List of 3
  ..$ attrs:'data.frame':   138 obs. of  7 variables:
  .. ..$ id       : num [1:138] 29158308 31175543 45749525 51104371 60186141 ...
  .. ..$ visible  : Factor w/ 1 level "true": 1 1 1 1 1 1 1 1 1 1 ...
  .. ..$ timestamp: POSIXlt[1:138], format: "2014-10-13 12:16:16" "2014-05-18 20:22:47" "2014-10-13 12:17:01" ...
  .. ..$ version  : num [1:138] 17 4 15 8 5 4 8 3 10 27 ...
  .. ..$ changeset: num [1:138] 26046342 22413405 26046342 20050162 22413405 ...
  .. ..$ user     : Factor w/ 8 levels "bibi6","escada",..: 7 7 7 8 7 8 8 8 1 7 ...
  .. ..$ uid      : Factor w/ 8 levels "145231","2449622",..: 7 7 7 1 7 1 1 1 5 7 ...
  ..$ tags :'data.frame':   855 obs. of  3 variables:
  .. ..$ id: num [1:855] 29158308 29158308 29158308 29158308 29158308 ...
  .. ..$ k : Factor w/ 19 levels "admin_level",..: 1 4 5 8 9 10 11 12 13 14 ...
  .. ..$ v : Factor w/ 41 levels "2","2009-10-20 00:00:02",..: 1 20 7 15 17 16 14 18 13 41 ...
  ..$ refs :'data.frame':   4473 obs. of  2 variables:
  .. ..$ id : num [1:4473] 29158308 29158308 29158308 29158308 29158308 ...
  .. ..$ ref: num [1:4473] 3.21e+08 3.21e+08 3.21e+08 3.21e+08 3.21e+08 ...
  ..- attr(*, "class")= chr [1:3] "ways" "osmar_element" "list"
 $ relations:List of 3
  ..$ attrs:'data.frame':   9 obs. of  7 variables:
  .. ..$ id       : num [1:9] 416271 2239171 2239750 2239123 2239751 ...
  .. ..$ visible  : Factor w/ 1 level "true": 1 1 1 1 1 1 1 1 1
  .. ..$ timestamp: POSIXlt[1:9], format: "2014-12-01 08:23:50" "2014-10-06 16:01:00" "2014-10-06 16:01:02" ...
  .. ..$ version  : num [1:9] 164 13 12 9 9 24 16 14 14
  .. ..$ changeset: num [1:9] 27148003 25898929 25898929 25898929 25898929 ...
  .. ..$ user     : Factor w/ 3 levels "Bas de Wit","QuercE",..: 1 2 2 2 2 3 2 2 3
  .. ..$ uid      : Factor w/ 3 levels "201359","2434393",..: 2 3 3 3 3 1 3 3 1
  ..$ tags :'data.frame':   121 obs. of  3 variables:
  .. ..$ id: num [1:121] 416271 416271 416271 416271 416271 ...
  .. ..$ k : Factor w/ 33 levels "admin_level",..: 1 2 3 5 6 8 9 11 18 28 ...
  .. ..$ v : Factor w/ 73 levels "30000","31000",..: 10 12 61 21 65 66 64 39 65 58 ...
  ..$ refs :'data.frame':   600 obs. of  4 variables:
  .. ..$ id  : num [1:600] 416271 416271 416271 416271 416271 ...
  .. ..$ type: Factor w/ 3 levels "node","relation",..: 1 1 3 3 3 3 3 3 3 3 ...
  .. ..$ ref : num [1:600] 2.70e+09 1.65e+09 4.11e+06 1.26e+08 1.69e+08 ...
  .. ..$ role: Factor w/ 4 levels "admin_centre",..: 2 1 3 3 3 3 3 3 3 3 ...
  ..- attr(*, "class")= chr [1:3] "relations" "osmar_element" "list"
 - attr(*, "class")= chr [1:2] "osmar" "list"

One first problem I see is that the ways are not in the same order as shown on the OSM website. On the OSM website, it seems that ways are ordered correctly. In the osmar object, the order seems random. Any idea how I can merge these ways into a closed polygon ?

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2 回答 2

5

只是想我会发布我现在使用的解决方案：

library(osmar)
library(rgeos)

wv <- get_osm(relation(416271), full=T)
wv_lines <- as_sp(wv, 'lines')
wv_lines_closed <- gLineMerge(wv_lines)

list_of_Lines <- slot(wv_lines_closed, "lines")
wv_polygon <- SpatialPolygons(lapply(list_of_Lines, function(x) {
  Polygons(list(Polygon(slot(slot(x, "Lines")[[1]], "coords"))),
           ID=slot(x, "ID"))
}),
proj4string=CRS("+proj=longlat +ellps=WGS84"))
plot(wv_polygon, col='red')
于 2014-12-10T20:40:06.990 回答
3

关系元素不必正确排序。事实上，甚至不可能为某些类型的关系找到合适的排序。

要订购关系元素，请查看元素本身。一种方式总是以特定的节点ID 开始和结束。连续的方式将始终在开始或结束时共享相同的节点 ID。对于排序，您只需确定哪些方式在开始和结束时共享相同的节点 ID。这只有在关系没有中断的情况下才有效，不幸的是，这可能不时发生。

这个相关的问题也可能对您有所帮助。

于 2014-12-10T14:43:59.153 回答