Introduction to GLATOS Data Processing

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

GLATOS 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.

First, we must set our working directory and import the relevant library.

## Set your working directory ####

setwd("./code/glatos/")
library(glatos)

Your code may not be in the ‘code/glatos’ folder, so use the appropriate file path for your data.

Next, we will create paths to our detections and receiver files. GLATOS can function with both GLATOS and OTN-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 will use the NSBS Blue Shark detections that come bundled with GLATOS. Please read the system.file documentation to understand how to load your own data from its location. You may not need to use the system.file command to build the path if the data is stored in the same place you’re running your script from.

# Get file path to example blue shark OTN data
det_file_name <- system.file("extdata", "blue_shark_detections.csv",
                        package = "glatos")

# Receiver Location
rec_file_name <- system.file("extdata", "hfx_deployments.csv",
                               package = "glatos")

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

With our file path 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 OTN style- if it were GLATOS formatted, we would want to use read_glatos_detections() instead.

# Save our detections file data into a dataframe called detections
detections <- read_otn_detections(det_file=det_file_name)

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)

We can do the same for our receivers with the read_otn_deployments function.

?read_otn_deployments
# Save receiver information into receivers dataframe

receivers <- read_otn_deployments(rec_file_name)
head(receivers, 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.

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

# write the filtered data (no rows deleted, just a filter column added)
# to a new det_filtered object
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 ####

# By animal ====
sum_animal <- summarize_detections(detections_filtered, 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='glatos_array', summ_type='location')

head(sum_location)

Finally, we can summarize by both dimensions.

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

head(sum_animal_location)

One other method- we can 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("NSBS-Alison", "NSBS-Brandy", "NSBS-Hey Jude")

sum_animal_custom <- summarize_detections(det=detections_filtered,
                                          animals=tagged_fish,
                                          summ_type='animal')

sum_animal_custom

Alright, we can summarize our data. Let’s move on and see if we can 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, GLATOS lets us to this easily.

# Reduce Detections to Detection Events ####

# ?glatos::detection_events
# arrival and departure time instead of multiple detection rows
# you specify how long an animal must be absent before starting a fresh event

events <- detection_events(detections_filtered,
                           location_col = 'station', # combines events across different receivers in a single array
                           time_sep=432000)

head(events)

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', # combines events across different receivers in a single array
                                        time_sep=432000, condense=FALSE)

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

Key Points