wk
The goal of wk is to provide lightweight R and C++ infrastructure for packages to use well-known formats (well-known binary and well-known text) as input and/or output without requiring external software. Well-known binary is very fast to read and write, whereas well-known text is human-readable and human-writable. Together, these formats allow for efficient interchange between software packages (WKB), and highly readable tests and examples (WKT).
Installation
You can install the released version of wk from CRAN with:
install.packages("wk")
You can install the development version from GitHub with:
# install.packages("remotes")
remotes::install_github("paleolimbot/wk")
If you can load the package, you’re good to go!
library(wk)
Basic vector classes for WKT and WKB
Use wkt()
to mark a character vector as containing well-known text, or
wkb()
to mark a vector as well-known binary. These have some basic
vector features built in, which means you can subset, repeat,
concatenate, and put these objects in a data frame or tibble. These come
with built-in format()
and print()
methods.
wkt("POINT (30 10)")
#> <wk_wkt[1]>
#> [1] POINT (30 10)
as_wkb(wkt("POINT (30 10)"))
#> <wk_wkb[1]>
#> [1] <POINT (30 10)>
Well-known R objects
The wk package experimentally generates (and parses) a plain R object
format, which is needed because well-known binary can’t natively
represent the empty point and reading/writing well-known text is too
slow. The format of the wksxp()
object is designed to be as close as
possible to well-known text and well-known binary to make the
translation code as clean as possible.
wkt_translate_wksxp("POINT (30 10)")
#> [[1]]
#> [,1] [,2]
#> [1,] 30 10
#> attr(,"class")
#> [1] "wk_point"
wkutils
To keep the footprint (i.e., compile time) of this package as slim as
possible, utilities to work with WKT, WKB, and well-known R objects are
located in the wkutils
package. One of the main
drawbacks to passing around geometries in WKB is that the format is
opaque to R users, who need coordinates as R objects rather than binary
vectors. The wkutils package provides wk*_meta()
and wk*_coords()
functions (among others) to extract usable coordinates and feature meta.
wkutils::wkt_coords("POINT ZM (1 2 3 4)")
#> # A tibble: 1 x 7
#> feature_id part_id ring_id x y z m
#> <int> <int> <int> <dbl> <dbl> <dbl> <dbl>
#> 1 1 1 0 1 2 3 4
wkutils::wkt_meta("POINT ZM (1 2 3 4)")
#> # A tibble: 1 x 7
#> feature_id part_id type_id size srid has_z has_m
#> <int> <int> <int> <int> <int> <lgl> <lgl>
#> 1 1 1 1 1 NA TRUE TRUE
wkutils::wkt_ranges("POINT ZM (1 2 3 4)")
#> # A tibble: 1 x 8
#> xmin ymin zmin mmin xmax ymax zmax mmax
#> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 1 2 3 4 1 2 3 4
wkutils::coords_point_translate_wkt(1, 2, 3, 4)
#> [1] "POINT ZM (1 2 3 4)"
Dependencies
The wk package imports Rcpp.
Using the C++ headers
The wk package takes an event-based approach to parsing inspired by the
event-based SAX XML parser. This makes the readers and writers highly
re-usable! This system is class-based, so you will have to make your
own subclass of WKGeometryHandler
and wire it up to a WKReader
to do
anything useful.
// If you're writing code in a package, you'll also
// have to put 'wk' in your `LinkingTo:` description field
// [[Rcpp::depends(wk)]]
#include <Rcpp.h>
#include "wk/rcpp-io.hpp"
#include "wk/wkt-reader.hpp"
using namespace Rcpp;
class CustomHandler: public WKGeometryHandler {
public:
void nextFeatureStart(size_t featureId) {
Rcout << "Do something before feature " << featureId << "\n";
}
void nextFeatureEnd(size_t featureId) {
Rcout << "Do something after feature " << featureId << "\n";
}
};
// [[Rcpp::export]]
void wkt_read_custom(CharacterVector wkt) {
WKCharacterVectorProvider provider(wkt);
WKTReader reader(provider);
CustomHandler handler;
reader.setHandler(&handler);
while (reader.hasNextFeature()) {
reader.iterateFeature();
}
}
On our example point, this prints the following:
wkt_read_custom("POINT (30 10)")
#> Do something before feature 0
#> Do something after feature 0
The full handler interface includes methods for the start and end of
features, geometries (which may be nested), linear rings, coordinates,
and parse errors. You can preview what will get called for a given
geometry using wkutils::wkb|wkt_debug()
functions.
library(wkutils) # remotes::install_github("paleolimbot/wkutils")
#> Warning: package 'wkutils' was built under R version 4.0.2
wkt_debug("POINT (30 10)")
#> nextFeatureStart(0)
#> nextGeometryStart(POINT [1], WKReader::PART_ID_NONE)
#> nextCoordinate(POINT [1], WKCoord(x = 30, y = 10), 0)
#> nextGeometryEnd(POINT [1], WKReader::PART_ID_NONE)
#> nextFeatureEnd(0)
Performance
This package was designed to stand alone and be flexible, but also happens to be really fast for some common operations.
Read WKB + Write WKB:
bench::mark(
wk = wk:::wksxp_translate_wkb(wk:::wkb_translate_wksxp(nc_wkb)),
sf = sf:::CPL_read_wkb(sf:::CPL_write_wkb(nc_sfc, EWKB = TRUE), EWKB = TRUE),
check = FALSE
)
#> # A tibble: 2 x 6
#> expression min median `itr/sec` mem_alloc `gc/sec`
#> <bch:expr> <bch:tm> <bch:tm> <dbl> <bch:byt> <dbl>
#> 1 wk 236µs 300µs 3072. 110.1KB 21.3
#> 2 sf 425µs 548µs 1523. 99.1KB 12.4
Read WKB + Write WKT:
bench::mark(
wk = wk:::wkb_translate_wkt(nc_wkb),
sf = sf:::st_as_text.sfc(sf:::st_as_sfc.WKB(nc_WKB, EWKB = TRUE)),
check = FALSE
)
#> Warning: Some expressions had a GC in every iteration; so filtering is disabled.
#> # A tibble: 2 x 6
#> expression min median `itr/sec` mem_alloc `gc/sec`
#> <bch:expr> <bch:tm> <bch:tm> <dbl> <bch:byt> <dbl>
#> 1 wk 3.13ms 4.63ms 209. 3.32KB 0
#> 2 sf 246.44ms 255.17ms 3.92 566.67KB 17.6
Read WKT + Write WKB:
bench::mark(
wk = wk:::wkt_translate_wkb(nc_wkt),
sf = sf:::CPL_write_wkb(sf:::st_as_sfc.character(nc_wkt), EWKB = TRUE),
check = FALSE
)
#> # A tibble: 2 x 6
#> expression min median `itr/sec` mem_alloc `gc/sec`
#> <bch:expr> <bch:tm> <bch:tm> <dbl> <bch:byt> <dbl>
#> 1 wk 2.12ms 2.38ms 387. 49.5KB 2.03
#> 2 sf 3.67ms 5.71ms 165. 185.7KB 4.24
Read WKT + Write WKT:
bench::mark(
wk = wk::wksxp_translate_wkt(wk::wkt_translate_wksxp(nc_wkt)),
sf = sf:::st_as_text.sfc(sf:::st_as_sfc.character(nc_wkt)),
check = FALSE
)
#> Warning: Some expressions had a GC in every iteration; so filtering is disabled.
#> # A tibble: 2 x 6
#> expression min median `itr/sec` mem_alloc `gc/sec`
#> <bch:expr> <bch:tm> <bch:tm> <dbl> <bch:byt> <dbl>
#> 1 wk 5.26ms 6.9ms 123. 63.8KB 1.99
#> 2 sf 254.41ms 254.5ms 3.93 234.9KB 17.7