test_pp_swift: Test locational accuracy of PinPoint Swift fixes against a...

In adamdsmith/pinpoint: Scheduling fixes and reading and plotting data from Lotek PinPoint tags

Description

This function evaluates the locational accuracy of PinPoint Swift fixes by comparing them to an input reference coordinate (i.e., tag location in lat/long decimal degrees WGS84). The most convenient input is a 'pp_df' class data.frame produced by read_pp_swift. Failed GPS fix attempts are removed automatically. Users can optionally filter GPS fixes by the reported horizontal dilution of precision 'max_hdop' or the number of satellites 'min_sats'. Limited experimentation finds fixes with at least 4 satellites and an HDOP <= 20 and to be of adequate locational quality, with an RMS of about 20 m (see details). These are the defaults. For larger scale studies, fixes from 3 satellites may also be useful.

Usage

test_pp_swift(pp_df, ref_coords = c(-83.36, 33.95), min_sats = 4,
  max_hdop = 20)

Arguments

pp_df	a 'pp_df' object (i.e., a 'data.frame' created by read_pp_swift)
ref_coords	a vector of coordinates (decimal degrees, WGS84 datum) of the reference location in the form c(longitude, latitude).
min_sats	numeric/integer scalar indicating the minimum number of satellites required (default is 4) to accept a GPS fix as valid.
max_hdop	numeric scalar indicating the maximum dilution of precision (default is <= 20) to accept a GPS fix as valid.

Details

The reported 2-D RMS error assumes that errors in the north-south and east-west directions are equivalent (i.e., that locational fixes describe a circular distribution around the true position; likely reasonable with >= 4 satellites). Assuming also that mean positional error is zero (or close to it), RMS is essentially equivalent to 1 standard devation, which in the two-directional case means that a circle of radius RMS is expected to contain about 63% of positional locations on average; double it for the 95% equivalent. See Diggelen (2007) for more details: http://gpsworld.com/gpsgnss-accuracy-lies-damn-lies-and-statistics-1134/)

Value

A histogram of locational errors (with median highlighted) and a report of 2-D RMS error by tag ID, and a 'pp_df' object containing the input data and two new columns:

• error_l - the absolute locational error, in meters

• error_b - the bearing of the locational error, in degrees from north

Examples

## Not run: 
# Select apprpriate text files from file selection window that opens
pp_tests <- list.files(path = system.file("extdata", package = "pinpoint"), full.names = TRUE)
dat <- read_pp_swift(pp_tests)
dat <- test_pp_swift(dat, ref_coords = c(-83.360298, 33.895814))
dat <- test_pp_swift(dat, min_sats = 9, ref_coords = c(-83.360298, 33.895814))

## End(Not run)

adamdsmith/pinpoint documentation built on Aug. 12, 2021, 12:53 a.m.