parzer: Parse Messy Geographic Coordinates

  Scott Chamberlain MARCH 19, 2020

parzer is a new package for handling messy geographic coordinates. The first version is now on CRAN, with binaries coming soon hopefully (see note about installation below). The package recently completed rOpenSci review.

parzer motivation

The idea for this package started with a tweet from Noam Ross (https://twitter.com/noamross/status/1070733367522590721) about 15 months ago.

The idea being that sometimes you have geographic coordinates in a messy format, or in many different formats, etc. You can think of it as being the package for geographic coordinates that lubridate is for dates.

I started off thinking about wrapping a Javascript library with Jeroen’s V8 R package, but then someone showed me or I found (can’t remember) some C++ code from back in 2006 that seemed appropriate. I figured I’d go down the C++ track instead of the Javascript track because I figured I could likely get better performance out of C++ and have slightly less install headaches for users.

Package installation

The package is on CRAN so you can use install.packages

install.packages("parzer")

However, since this package requires compilation you probably want a binary. Binaries are not available on CRAN yet. You can install a binary like

install.packages("parzer", repos = "https://dev.ropensci.org/")
library(parzer)

Check out the package documentation to get started: https://docs.ropensci.org/parzer/



Package basics

The following is a summary of the functions in the package and what they do:

Parse latitude or longitude separately

  • parse_lat
  • parse_lon

Parse latitudes and longitudes at the same time

  • parse_lon_lat

Parse into separate parts of degrees, minutes, seconds

  • parse_parts_lat
  • parse_parts_lon

Pull out separately degrees, minutes, seconds, or hemisphere

  • pz_degree
  • pz_minute
  • pz_second
  • parse_hemisphere

Add/subtract degrees, minutes, seconds

  • pz_d
  • pz_m
  • pz_s

Some examples:

parse latitudes and longitudes

lats <- c("40.123°", "40.123N74.123W", "191.89", 12, "N45 04.25764")
parse_lat(lats)
#> Warning in pz_parse_lat(lat): invalid characters, got: 40.123n74.123w

#> Warning in pz_parse_lat(lat): not within -90/90 range, got: 191.89
#>   check that you did not invert lon and lat

#> [1] 40.12300      NaN      NaN 12.00000 45.07096
longs <- c("45W54.2356", "181", 45, 45.234234, "-45.98739874N")
parse_lon(longs)
#> Warning in pz_parse_lon(lon): invalid characters, got: -45.98739874n

#> [1] -45.90393 181.00000  45.00000  45.23423       NaN

In the above examples you can see there’s a mix of valid coordinate values as well as invalid values. There’s a mix of types supported as well.

Sometimes you may want to parse a geographic coordinate into its component parts; parse_parts_lat and parse_parts_lon are what you need:

x <- c("191.89", 12, "N45 04.25764")
parse_parts_lon(x)
#> Warning in pz_parse_parts_lon(scrub(str)): invalid characters, got: n45 04.25764

#>   deg min      sec
#> 1 191  53 23.99783
#> 2  12   0  0.00000
#> 3  NA  NA      NaN

Taking a cue from lubridate, we thought it would be useful to make it easier to add or subtract numbers for coordinates. Three functions help with this:

pz_d(31)
#> 31
pz_d(31) + pz_m(44)
#> 31.73333
pz_d(31) - pz_m(44)
#> 30.26667
pz_d(31) + pz_m(44) + pz_s(59)
#> 31.74972
pz_d(-121) + pz_m(1) + pz_s(33)
#> -120.9742



Use cases

Check out the parzer use cases vignette on the docs site. Get in touch if you have a use case that might be good to add to that vignette.

Thanks

Thanks to the reviewers Maria Munafó and Julien Brun for their time invested in improving the package.

To Do

There’s more to do. We are thinking about dropping the Rcpp dependency, support parsing strings that have both latitude and longitude together, making error messages better, and more.


geospatial parzer software peer review R