post_table is a spatio-temporal tabular data structure that
organises polygons that change their shape in space and time.
It extends the cubble_df classes for vector data cubes to support
changing geometries in the temporal face of the cube.
The post_table geometry for the spatial face of the cube defaults
to a column named geom_sum, while the changing geometry provided is
passed on to the temporal face of the cube.
Usage
as_post_table(
x,
group_id = NULL,
time_column_name = NULL,
sf_column_name = NULL,
geometry_summary = summarise_geometry_centroid,
...
)
# S3 method for class 'sf'
as_post_table(
x,
group_id = NULL,
time_column_name = NULL,
sf_column_name = NULL,
geometry_summary = summarise_geometry_centroid,
...
)
# S3 method for class 'post_array'
as_post_table(x, ..., drop_empty = TRUE)
# S3 method for class 'post_table'
as_post_table(x, ...)Arguments
- x
object to convert to
post_tablewithPOLYGON/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.- ...
additional parameters passed on to
geometry_summaryfunction.- drop_empty
(logical) should empty geometries be dropped during post_table creation? Defaults to TRUE
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_table(polygons)
#> # cubble: key: gid [5], index: datetime, nested form, [sf]
#> # spatial: [0, 0.18, 0.75, 0.9], WGS 84
#> # temporal: datetime [date], geometry [POLYGON [°]]
#> gid long lat geom_sum ts
#> * <chr> <dbl> <dbl> <POINT [°]> <list>
#> 1 a 0.648 0.902 (0.647816 0.9018588) <sf [5 × 2]>
#> 2 b -0.00254 0.840 (-0.002543201 0.8403816) <sf [5 × 2]>
#> 3 c 0.390 0.541 (0.3897167 0.5412363) <sf [5 × 2]>
#> 4 d 0.753 0.354 (0.752585 0.3538271) <sf [5 × 2]>
#> 5 e 0.469 0.178 (0.4690683 0.17772) <sf [5 × 2]>
if(require(dplyr, quietly = TRUE)) {
library(sf, quietly = TRUE)
polygons |>
mutate(area = st_area(geometry)) |>
as_post_table(
geometry_summary = summarise_geometry_union
)
}
#> Warning: st_centroid assumes attributes are constant over geometries
#> # cubble: key: gid [5], index: datetime, nested form, [sf]
#> # spatial: [-0.3, 0, 0.97, 1.15], WGS 84
#> # temporal: datetime [date], area [[m^2]], geometry [POLYGON [°]]
#> gid long lat geom_sum ts
#> * <chr> <dbl> <dbl> <POLYGON [°]> <lis>
#> 1 a 0.648 0.902 ((0.4971355 0.8717961, 0.5474949 0.8088912, 0.5905… <sf>
#> 2 b -0.00254 0.840 ((-0.1774445 0.5995572, -0.1843257 0.5881332, 0.37… <sf>
#> 3 c 0.390 0.541 ((0.28657 0.6085207, 0.2663408 0.6222649, 0.214584… <sf>
#> 4 d 0.753 0.354 ((0.5737123 0.4613799, 0.6063966 0.4263975, 0.5272… <sf>
#> 5 e 0.469 0.178 ((0.2973931 0.2557416, 0.2813385 0.2544898, 0.2452… <sf>