post_array is a spatio-temporal array data structure that
organises polygons that change their shape in space and time.
It extends the stars class for vector data cubes to support
changing geometries as attributes.
The post_array class supports two dimensions: a summary geometry
dimension (default name: geom_sum) and a temporal dimension.
The summary geometry is a unique geometry per group
which summarises the changing shapes of the polygon geometries in the group.
Usage
as_post_array(
x,
group_id = NULL,
time_column_name = NULL,
sf_column_name = NULL,
geometry_summary = summarise_geometry_centroid,
geometry_summary_name = NULL,
...
)
# S3 method for class 'sf'
as_post_array(
x,
group_id = NULL,
time_column_name = NULL,
sf_column_name = NULL,
geometry_summary = summarise_geometry_centroid,
geometry_summary_name = NULL,
...,
point_st = c(TRUE, FALSE)
)
# S3 method for class 'post_table'
as_post_array(x, ...)
# S3 method for class 'post_array'
as_post_array(x, ...)Arguments
- x
object to convert to
post_arraywithPOLYGON/MULTIPOLYGONgeometries and a date/time column.- group_id
See Details. Defaults to the first non-spatial, non-temporal column in
x.- time_column_name
(character) name of column with the temporal dimension information. Defaults to the first temporal column in
x.- sf_column_name
(character) name of column with changing geometries. Defaults to active
sf_column.- geometry_summary
(function) function to compute the summary geometry. Alternatively an
sfcobject with summary geometries (i.e., the result of asummarise_geometry_*()function or a customsfc). See summarise_geometry for functions or pass your own summarise_geometry function.- geometry_summary_name
(character) name of the column with summary geometries.Defaults to "geom_sum"
- ...
additional parameters passed on to
geometry_summaryfunction.- point_st
point argument passed onto
stars::st_dimensions(). Defaults toTRUEfor the spatial dimension and toFALSEfor the temporal dimension (assumes interval times)
Details
group_id should be the name of the column containing the grouping
identifier for the changing polygons or a vector with group identifiers.
Character, integer, double and factor vectors are supported.
The vector should be of length 1 or the same as nrow(x).
A vector of length 1 repeats the value for all the rows.
Providing a vector assumes that the ordering of the groups
is correct and that there are no duplicated timestamps per group
References
Abad, L., Sudmanns, M., and Hölbling, D. (2024) Vector data cubes for features evolving in space and time, AGILE GIScience Ser., 5, 16, https://doi.org/10.5194/agile-giss-5-16-2024
Examples
as_post_array(polygons)
#> stars object with 2 dimensions and 1 attribute
#> attribute(s):
#> geometry
#> POLYGON :25
#> epsg:4326 : 0
#> +proj=long...: 0
#> dimension(s):
#> from to offset delta refsys point
#> geom_sum 1 5 NA NA WGS 84 TRUE
#> datetime 1 5 2020-10-01 1 days Date FALSE
#> values
#> geom_sum POINT (0.647816 0.9018588),...,POINT (0.4690683 0.17772)
#> datetime NULL
if(require(dplyr, quietly = TRUE)) {
library(sf, quietly = TRUE)
polygons |>
mutate(area = st_area(geometry)) |>
as_post_array(
geometry_summary = summarise_geometry_union
)
}
#>
#> Attaching package: ‘dplyr’
#> The following objects are masked from ‘package:stats’:
#>
#> filter, lag
#> The following objects are masked from ‘package:base’:
#>
#> intersect, setdiff, setequal, union
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE
#> stars object with 2 dimensions and 2 attributes
#> attribute(s):
#> geometry area
#> POLYGON :25 Min. :5.366e+07
#> epsg:4326 : 0 1st Qu.:3.928e+08
#> +proj=long...: 0 Median :4.060e+08
#> Mean :6.216e+08
#> 3rd Qu.:6.933e+08
#> Max. :1.537e+09
#> dimension(s):
#> from to offset delta refsys point
#> geom_sum 1 5 NA NA WGS 84 FALSE
#> datetime 1 5 2020-10-01 1 days Date FALSE
#> values
#> geom_sum POLYGON ((0.4971355 0.871...,...,POLYGON ((0.2973931 0.255...
#> datetime NULL