silicate
is a new
form for representing spatial data in R. In contrast to all
other forms (such as sp
or
sf
),
silicate
is multi-tabular, and
primarily consists of one table for point entities; one table for binary
relationships between these point entities -- spatial ''edges'' -- and
additional tables for higher-order inter-relationships between these objects.
The new osmdata
function osmdata_sc()
returns Open Street Map (OSM) data in
silicate
form. This form also closely
resembles the data storage scheme of Open Street Map itself, and in this case
consists of the following tables:
vertex
table holding the coordinates of all OSM nodes;edge
table mapping all edge connections between vertices;object_link_edge
table linking all edge
entities to the OSM objects of
which they are part;object
table holding all 'key'--'value' pairs for each OSM way object;relation_properties
table holding all 'key'--'value' pairs for each OSM
relation object;relation_members
table holding all members of each OSM relation; andnodes
table holding all 'key'--'value' pairs for each OSM node object.The translation of the underlying OSM data structure -- consisting of nodes,
way, and relations -- into
Simple Features (SF) via the
osmdata_sf()
function is less than 100% faithful, and results in some representational loss
compared with the original OSM structure (for details, see the vignette on
translation of OSM into
SF). In
contrast, the osmdata_sc()
function delivers
a representation that is entirely faithful to the underlying OSM representation.
One of the advantages of silicate
format offered by the osmdata
package is enabling elevation data to be
combined with OSM data. The result is
a silicate
-format object which is
able to be submitted directly to the dodgr
package to enable routing on street
networks that accounts for elevation changes.
Incorporating elevation data with OSM data currently requires local storage of
desired elevation data. These must be downloaded for the desired region from
http://srtm.csi.cgiar.org/srtmdata in Geo
TIFF format. Elevation data may then be incorporated with
silicate
-format data generated by
x <- osmdata_sc()
through the osm_elevation()
function. The entire procedure is demonstrated
with the following lines:
dat <- opq ("omaha nebraska") %>% add_osm_feature (key = "highway") %>% osmdata_sc ()
This object has a vertex
table like this:
dat$vertex
n <- 345239 x_ <- c (-95.9, -95.9, -95.9, -95.9, -95.9, -95.9, -96.2, -96.2, -96.3, -96.3) y_ <- c (41.2, 41.2, 41.2, 41.2, 41.2, 41.2, 41.3, 41.3, 41.3, 41.3) z_ <- c (291.0, 295.0, 297.0, 301.0, 295.0, 300.0, 359.0, 359.0, 358.0, 358.0) vertex_ <- paste0 (c ( 31536366, 31536367, 31536368, 31536370, 31536378, 31536379, 133898322, 133898328, 133898340, 133898342 )) tibble::tibble ( x_ = c (x_, rep (NA, n - 10)), y_ = c (y_, rep (NA, n - 10)), vertex_ = c (vertex_, rep (NA, n - 10)) )
Incorporating elevation data is then as simple as
dat <- osm_elevation (dat, elev_file = "/path/to/elevation/data/filename.tiff")
message ( "Loading required namespace: raster\n", "Elevation data from Consortium for Spatial Information; see ", "https://srtm.csi.cgiar.org/srtmdata/" )
This function then simply appends the elevation values to the vertex_
table,
so that it now looks like this:
dat$vertex_
tibble::tibble ( x_ = c (x_, rep (NA, n - 10)), y_ = c (y_, rep (NA, n - 10)), z_ = c (z_, rep (NA, n - 10)), vertex_ = c (vertex_, rep (NA, n - 10)) )
The silicate
format is very easy to
manipulate using standard dplyr
verbs. The
following code uses the mapdeck
package package to colour the street
network and elevation data downloaded and processed in the preceding lines by
the elevation of each network edge. We first join the vertex elevation data on
to the edges, and calculate the mean elevation of each edge.
edges <- dplyr::left_join (dat$edge, dat$vertex, by = c (".vx0" = "vertex_")) %>% dplyr::rename (".vx0_x" = x_, ".vx0_y" = y_, ".vx0_z" = z_) %>% dplyr::left_join (dat$vertex, by = c (".vx1" = "vertex_")) %>% dplyr::rename (".vx1_x" = x_, ".vx1_y" = y_, ".vx1_z" = z_) %>% dplyr::mutate ("zmn" = (.vx0_z + .vx1_z) / 2) %>% dplyr::select (-c (.vx0_z, .vx1_z)) edges
n <- 376370 x <- paste0 (c ( 1903265686, 1903265664, 1903265638, 1903265710, 1903265636, 1903265685, 1903265678, 1903265646, 1903265714, 1903265659 )) y <- paste0 (c ( 1903265664, 1903265638, 1903265710, 1903265636, 1903265685, 1903265678, 1903265646, 1903265714, 1903265659, 1903265702 )) edge <- c ( "V6kgqvWjtM", "mX4HQkykiD", "26e5NHT8nI", "9TOmVAvGH4", "hYbpf832vX", "ctvd1FWGEw", "mvaAOdSOKA", "dSVFPNDFty", "uc8L3jGR87", "MpjXnvIvcF" ) x0_x <- c (-96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2) x0_y <- c (41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3) x1_x <- c (-96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2, -96.2) x1_y <- c (41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3, 41.3) z <- c (351.0, 352.0, 352.0, 352.0, 352.0, 352.0, 352.0, 352.0, 352.0, 352.0) tibble::tibble ( ".vx0" = c (x, rep (NA, n - 10)), ".vx1" = c (y, rep (NA, n - 10)), "edge_" = c (edge, rep (NA, n - 10)), ".vx0_x" = c (x0_x, rep (NA, n - 10)), ".vx0_y" = c (x0_y, rep (NA, n - 10)), ".vx1_x" = c (x1_x, rep (NA, n - 10)), ".vx1_y" = c (x1_y, rep (NA, n - 10)), "zmn" = c (z, rep (NA, n - 10)) )
Those data can then be submitted directly to
mapdeck
to generate an interactive
plot with the following code:
library (mapdeck) set_token (Sys.getenv ("MAPBOX_TOKEN")) # load local token for MapBox mapdeck (style = mapdeck_style ("dark")) %>% add_line (edges, origin = c (".vx0_x", ".vx0_y"), destination = c (".vx1_x", ".vx1_y"), stroke_colour = "z", legend = TRUE )
(The result is not shown here, but can be directly inspected by simply running the above lines.)
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