guess_crs {crsuggest}R Documentation

Guess the CRS of a dataset that is missing CRS information

Description

This function will "guess" possible coordinate reference systems for spatial data that are lacking a CRS definition. Input data, which must be of class "sf", might be objects created from CSV files that use projected coordinates or objects created from shapefiles loaded with sf::st_read() that are missing .prj files. The function requires a "target location" that the user knows to be within the general area of the input dataset. It then identifies suitable coordinate reference systems for that area and "tests out" those CRSs for the input data by analyzing the distance between the dataset and the known location when that CRS is used. Those distances are returned by the function in a column dist_km; short distances represent better guesses for the CRS whereas longer distances suggest that the CRS wouldn't work.

Usage

guess_crs(input_sf, target_location, units = NULL, n_return = 10)

Arguments

input_sf

An input sf object in a projected coordinate system that is missing CRS information. For example, you may have loaded in a shapefile without a .prj file, or your input data has no CRS definition attached.

target_location

A coordinate pair of form c(longitude, latitude) or an address/location that you know is located within your input sf object. If the mapboxapi package is installed, you can supply a location name (e.g. an address or a city) instead of a coordinate pair.

units

If known, the units of your projected coordinate system (e.g. "m" for meters or "us-ft" for US feet). This is not required but will make the guesses more accurate.

n_return

The number of possible CRS choices to return; defaults to 10. A higher number than that may include CRS options that are unlikely to work with your data. Use the returned dist_km column to judge whether the CRS guess makes sense for your data.

Value

A tibble of CRS guesses for your data, sorted in ascending order of distance between your target location and the input sf object's centroid when in that CRS.

Examples

## Not run: 
library(crsuggest)
library(sf)
# An example data frame of projected coordinates with no CRS information included
locations <- data.frame(
  X = c(2312654.74514528, 2357493.02092003, 2398978.30047505, 2344378.47525209,
        2475776.26735713, 2493751.94421798, 2456797.1698781, 2448392.13089886,
        2319704.35367616, 2350119.25250331, 2449088.54659236, 2423774.3668849),
  Y = c(6966055.04531077, 6994256.06222144, 6951975.79788762, 6902972.35980149,
        6918178.81070276, 6977643.56941746, 7053989.26343385, 7024543.36487243,
        7015476.52061313, 6953350.28550116, 6945011.24615857, 6912284.16691977),
  id = 1:12
)

# Create an sf object but the CRS is not known
locations_sf <- st_as_sf(locations, coords = c("X", "Y"))

# Use `guess_crs()` to guess the CRS used for the coordinates along with a known coordinate
# in the area of interest
guesses <- guess_crs(locations_sf, target_location = c(-97.1071, 32.7356))
# Set the CRS of your data with the "best guess"
st_crs(locations_sf) <- 6584

## End(Not run)

[Package crsuggest version 0.3.1 Index]