Filtering and Assessing the Sample Size of Tracking Data

Functions to filter GPS/Argos locations, as well as assessing the sample size for the analysis of animal distributions. The filters remove temporal and spatial duplicates, fixes located at a given height from estimated high tide line, and locations with high error as described in Shimada et al. (2012) and Shimada et al. (2016) . Sample size for the analysis of animal distributions can be assessed by the conventional area-based approach or the alternative probability-based approach as described in Shimada et al. (2021) .


SDLfilter contains a variety of functions to screen GPS and/or Argos locations, and to plot them on a map.


# Or the development version from GitHub:


There are three main filtering functions.

  1. dupfilter removes temporal and spatial duplicates.

  2. ddfilter removes locations with high error.

  3. depthfilter removes fixes located at a given height from estimated high tide line (e.g. locations on land).

Please see the help pages and Shimada et al. (2012, 2016) for more details.

### Fastloc GPS data obtained from a green turtle
### Remove temporal and spatial duplicates
turtle.dup <- dupfilter(turtle)
### Remove biologically unrealistic fixes 
turtle.dd <- ddfilter(turtle.dup, vmax=9.9, qi=4, ia=90, maxvlp=2.0)
### Plot the locations on a map
# unfiltered
plotMap(turtle, point.size = 2, line.size = 0.5, axes.lab.size = 0)
# filtered
plotMap(turtle.dd, point.size = 2, line.size = 0.5, axes.lab.size = 0,
        bgmap = "satellite", sb.line.col = "white", sb.text.col = "white")


If you use the function ddfilter, please cite

Shimada T, Jones R, Limpus C, Hamann M (2012) Improving data retention and home range estimates by data-driven screening. Mar Ecol Prog Ser 457:171-180

If you use the functions dupfilter or depthfilter, please cite

Shimada T, Limpus C, Jones R, Hazel J, Groom R, Hamann M (2016) Sea turtles return home after intentional displacement from coastal foraging areas. Mar Biol 163:1-14

Current version

1.2.1 (19 February 2019)


output: html_notebook editor_options: chunk_output_type: inline

News for Package 'SDLfilter'

Version 1.2.1 (2019-02-19)

  • amended "plotMap" in accordance with the ggsn update to version 0.5.0.

Version 1.2.0 (2019-02-18)

  • added a mew function "distance_filter". This function removes fixes located beyond a given threshold distance.
  • fixed bugs in the example codes.
  • amended "plotMap" in accordance with the ggmap update to version 3.0.0.

Version 1.1.1 (2018-06-10)

  • fixed minor bugs in the est.maxvlp function. The values estimated using the previous version would not have been affected by the changes. In the previous version, when sample size is too small (i.e. <6 fixes) or inner angles could not be estimated (e.g. two consecutive locations with the same coordinates), the function ceased with warning messages. These errors are now avoided by exuding those fixes from the estimation process.

Version 1.1.0 (2018-04-27)

  • added a new function ( to plot locations.
  • updated vignette.

Version 1.0.0 (2018-02-08)

  • First official release.

Reference manual

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2.1.2 by Takahiro Shimada, a month ago

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Browse source code at

Authors: Takahiro Shimada

Documentation:   PDF Manual  

Task views:

GPL-2 | file LICENSE license

Imports plotKML, sp, raster, trip, data.table, gridExtra, ggsn, stats, maps, pracma, plyr, ggmap, lubridate, dplyr

Depends on ggplot2

See at CRAN