Introduction to glatos Data Processing Package

Overview

Teaching: 30 min
Exercises: 0 min

Questions

• How do I load my data into glatos?

• How do I filter out false detections?

• How can I consolidate my detections into detection events?

• How do I summarize my data?

Objectives

The glatos package is a powerful toolkit that provides a wide range of functionality for loading, processing, and visualizing your data. With it, you can gain valuable insights with quick and easy commands that condense high volumes of base R into straightforward functions, with enough versatility to meet a variety of needs.

This package was originally created to meet the needs of the Great Lakes Acoustic Telemetry Observation System (GLATOS) and use their specific data formats. However, over time, the functionality has been expanded to allow operations on OTN-formatted data as well, broadening the range of possible applications for the software. As a point of clarification, “GLATOS” (all caps acronym) refers to the organization, while glatos refers to the package.

Our first step is setting our working directory and importing the relevant libraries.

## Set your working directory ####

setwd("./data/fact")
library(glatos)
library(tidyverse)
library(VTrack)
library(utils)
library(lubridate)

If you are following along with the workshop in the workshop repository, there should be a folder in ‘data/’ containing data corresponding to your node (at time of writing, FACT, ACT, or GLATOS). glatos can function with both GLATOS and OTN Node-formatted data, but the functions are different for each. Both, however, provide a marked performance boost over base R, and both ensure that the resulting data set will be compatible with the rest of the glatos framework.

We’ll start by combining our several data files into one master detection file, which glatos will be able to read.

format <- cols( # Heres a col spec to use when reading in the files
  .default = col_character(),
  datelastmodified = col_date(format = ""),
  bottom_depth = col_double(),
  receiver_depth = col_double(),
  sensorname = col_character(),
  sensorraw = col_character(),
  sensorvalue = col_character(),
  sensorunit = col_character(),
  datecollected = col_datetime(format = ""),
  longitude = col_double(),
  latitude = col_double(),
  yearcollected = col_double(),
  monthcollected = col_double(),
  daycollected = col_double(),
  julianday = col_double(),
  timeofday = col_double(),
  datereleasedtagger = col_logical(),
  datereleasedpublic = col_logical()
)

detections <- tibble()
for (detfile in list.files('.', full.names = TRUE, pattern = "tqcs.*\\.zip")) {
  print(detfile)
  tmp_dets <- read_csv(detfile, col_types = format)
  detections <- bind_rows(detections, tmp_dets)
}

write_csv(detections, 'all_dets.csv', append = FALSE)

With our new file in hand, we’ll want to use the read_otn_detections function to load our data into a dataframe. In this case, our data is formatted in the FACT (OTN) style- if it were GLATOS formatted, we would want to use read_glatos_detections() instead.

Remember: you can always check a function’s documentation by typing a question mark, followed by the name of the function.

## glatos help files are helpful!! ####
?read_otn_detections

# Save our detections file data into a dataframe called detections
detections <- read_otn_detections(det_file='all_dets.csv')

detections <- detections %>% slice(1:100000) # subset our example data to help this workshop run

Making a 100,000 row subset of our data is not a necessary step, but it will make our code run more smoothly for this workshop, since later functions can struggle with large datasets.

Remember that we can use head() to inspect a few lines of our data to ensure it was loaded properly.

# View first 2 rows of output
head(detections, 2)

With our data loaded, we next want to apply a false filtering algorithm to reduce the number of false detections in our dataset. glatos uses the Pincock algorithm to filter probable false detections based on the time lag between detections- tightly clustered detections are weighted as more likely to be true, while detections spaced out temporally will be marked as false. We can also pass the time-lag threshold as a variable to the false_detections function. This lets us fine-tune our filtering to allow for greater or lesser temporal space between detections before they’re flagged as false.

## Filtering False Detections ####
## ?glatos::false_detections

# write the filtered data to a new det_filtered object
#This doesn't delete any rows, it just adds a new column that tells you whether #or not a detection was filtered out.
detections_filtered <- false_detections(detections, tf=3600, show_plot=TRUE)
head(detections_filtered)
nrow(detections_filtered)

The false_detections function will add a new column to your dataframe, ‘passed_filter’. This contains a boolean value that will tell you whether or not that record passed the false detection filter. That information may be useful on its own merits; for now, we will just use it to filter out the false detections.

# Filter based on the column if you're happy with it.

detections_filtered <- detections_filtered[detections_filtered$passed_filter == 1,]
nrow(detections_filtered) # Smaller than before

With our data properly filtered, we can begin investigating it and developing some insights. glatos provides a range of tools for summarizing our data so that we can better see what our receivers are telling us.

We can begin with a summary by animal, which will group our data by the unique animals we’ve detected.

# Summarize Detections ####
#?summarize_detections
#summarize_detections(detections_filtered)

# By animal ====
sum_animal <- summarize_detections(detections_filtered, location_col = 'station', summ_type='animal')

sum_animal

We can also summarize by location, grouping our data by distinct locations.

# By location ====

sum_location <- summarize_detections(detections_filtered, location_col = 'station', summ_type='location')

head(sum_location)

summarize_detections will return different summaries depending on the summ_type parameter. It can take either “animal”, “location”, or “both”. More information on what these summaries return and how they are structured can be found in the help files (?summarize_detections).

If you had another column that describes the location of a detection, and you would prefer to use that, you can specify it in the function with the location_col parameter. In the example below, we will create a new column and use that as the location.

# You can make your own column and use that as the location_col
# For example we will create a uniq_station column for if you have duplicate station names across projects
detections_filtered_special <- detections_filtered %>%
  mutate(station_uniq = paste(glatos_array, station, sep=':'))

sum_location_special <- summarize_detections(detections_filtered_special, location_col = 'station_uniq', summ_type='location')

head(sum_location_special)

For the next example, we’ll summarise along both animal and location, as outlined above.

# By both dimensions
sum_animal_location <- summarize_detections(det = detections_filtered,
                                            location_col = 'station',
                                            summ_type='both')

head(sum_animal_location)

Summarising by both dimensions will create a row for each station and each animal pair. This can be a bit cluttered, so let’s use a filter to remove every row where the animal was not detected on the corresponding station.

# Filter out stations where the animal was NOT detected.
sum_animal_location <- sum_animal_location %>% filter(num_dets > 0)

sum_animal_location

One other method we can use is to summarize by a subset of our animals as well. If we only want to see summary data for a fixed set of animals, we can pass an array containing the animal_ids that we want to see summarized.

# create a custom vector of Animal IDs to pass to the summary function
# look only for these ids when doing your summary
tagged_fish <- c('TQCS-1049258-2008-02-14', 'TQCS-1049269-2008-02-28')

sum_animal_custom <- summarize_detections(det=detections_filtered,
                                          animals=tagged_fish,  # Supply the vector to the function
                                          location_col = 'station',
                                          summ_type='animal')

sum_animal_custom

Now that we have an overview of how to quickly and elegantly summarize our data, let’s make our dataset more amenable to plotting by reducing it from detections to detection events.

Detection Events differ from detections in that they condense a lot of temporally and spatially clustered detections for a single animal into a single detection event. This is a powerful and useful way to clean up the data, and makes it easier to present and clearer to read. Fortunately, this is easy to do with glatos.

# Reduce Detections to Detection Events ####

# ?glatos::detection_events
# you specify how long an animal must be absent before starting a fresh event

events <- detection_events(detections_filtered,
                           location_col = 'station',
                           time_sep=3600)

head(events)

location_col tells the function what to use as the locations by which to group the data, while time_sep tells it how much time has to elapse between sequential detections before the detection belongs to a new event (in this case, 3600 seconds, or an hour). The threshold for your data may be different depending on the purpose of your project.

We can also keep the full extent of our detections, but add a group column so that we can see how they would have been condensed.

# keep detections, but add a 'group' column for each event group
detections_w_events <- detection_events(detections_filtered,
                                        location_col = 'station',
                                        time_sep=3600, condense=FALSE)

With our filtered data in hand, let’s move on to some visualization.

Key Points