A locationID is created for each incoming longitude
and
latitude
. Each locationID is unique to within a certain spatial scale.
With algorithm = "geohash"
, the
precision
argument determines the size of a geohash grid cell. At the
equator, the following grid cell sizes apply for different precision levels:
precision (maximum grid cell X axis, in m)
5 ± 2400
6 ± 610
7 ± 76
8 ± 19
9 ± 2.4
10 ± 0.6
Invalid locations will be assigned a locationID specified by the user with
the invalidID
argument, typically NA
.
createLocationID(
longitude = NULL,
latitude = NULL,
algorithm = c("geohash", "digest"),
precision = 10,
invalidID = as.character(NA)
)
Vector of longitudes in decimal degrees E.
Vector of latitudes in decimal degrees N.
Algorithm to use -- either "geohash"
or "digest"
.
precision
argument used when encoding with "geohash"
.
Identifier to use for invalid locations. This can be a
character string or NA
.
Vector of character locationIDs.
When the "geohash"
algorithm is specified,
the following code is used to generate each locationID:
locationID <-
geohashTools::gh_encode(latitude, longitude, precision)
When the "digest"
algorithm is specified,
the following code is used:
# Retain accuracy up to ~.1m
locationString <- paste0(
sprintf("%.7f", longitude),
"_",
sprintf("%.7f", latitude)
)
# Avoid collisions until billions of records
locationID <- digest::digest(locationString, algo = "xxhash64")
See the references for details on either algorithm.
The "geohash"
algorithm is preferred but the "digest"
algorithm is retained because several existing databases
use the "digest"
algorithm as a unique identifier.
https://en.wikipedia.org/wiki/Decimal_degrees
https://www.johndcook.com/blog/2017/01/10/probability-of-secure-hash-collisions/
library(MazamaCoreUtils)
longitude <- c(-122.5, 0, NA, -122.5, -122.5)
latitude <- c( 47.5, 0, 47.5, NA, 47.5)
createLocationID(longitude, latitude)
#> [1] "c22yhrn5x1" NA NA NA "c22yhrn5x1"
createLocationID(longitude, latitude, invalidID = "bad")
#> [1] "c22yhrn5x1" "bad" "bad" "bad" "c22yhrn5x1"
createLocationID(longitude, latitude, algorithm = "digest")
#> [1] "00cf3f93141268b9" NA NA NA
#> [5] "00cf3f93141268b9"