1.1 Detections objects | kaltoa: Kalman Filtered Time-of-Arrival Positioning

1.1 `Detections` objects

The heart of kaltoa is the Detections object (see ?Detections). Along with detections data for a given receiver, this also holds useful metadata for the receiver’s position and sync-tags.

Below is a typical table of raw detection data we’ll use to build a Detections object.

head(example)

##                 timestamp detect_id     type
## 1 2021-05-08T18:00:09.427     62074      PPM
## 2 2021-05-08T18:00:38.772     62042      PPM
## 3 2021-05-08T18:00:48.244     62584      PPM
## 4 2021-05-08T18:01:03.878  PPM_SELF PPM_SELF
## 5 2021-05-08T18:02:21.749     62368      PPM
## 6 2021-05-08T18:05:23.948     62074      PPM

First, we’ll convert our detection ISO dates-time strings into a more handy format.

# Convert times into numeric values
detect_time <- iso2DetectionTime(example$timestamp, tz = "CET")
# Preview detection times
head(detect_time)

## Time zone: CET
##                second millisecond
## 1 2021-05-08 18:00:09         427
## 2 2021-05-08 18:00:38         772
## 3 2021-05-08 18:00:48         244
## 4 2021-05-08 18:01:03         878
## 5 2021-05-08 18:02:21         749
## 6 2021-05-08 18:05:23         948

Here, the column titled second holds POSIX times — the number of seconds since 1970-01-01.

Now we’ll put this into a Detections object.

detect <- Detections(
  detect_times = detect_time, 
  detect_id = example$detect_id,
  x = 481472, y = 6243509, depth = 3,
  emit_id = "62041",
  name = "1",
  type = example$type, 
  sync_emissions = example$type %in% c("PPM_SELF", "HR_SELF"))

head(detect)

## Telemetry Detections
## Name: 1
## Sync-tag ID: 62041
## Depth: 3
## Coords: (481472 m, 6243509 m)
## Sync tag emissions: 1
## Detections: 5
## First detection on: 2021-05-08 18:00:09
## Last detection on: 2021-05-08 18:05:23
## Time zone: CET
##                second millisecond detect_id     type sync_emission
## 1 2021-05-08 18:00:09         427     62074      PPM         FALSE
## 2 2021-05-08 18:00:38         772     62042      PPM         FALSE
## 3 2021-05-08 18:00:48         244     62584      PPM         FALSE
## 4 2021-05-08 18:01:03         878  PPM_SELF PPM_SELF          TRUE
## 5 2021-05-08 18:02:21         749     62368      PPM         FALSE
## 6 2021-05-08 18:05:23         948     62074      PPM         FALSE

kaltoa uses sync-tags to align the receiver clocks in a telemetry array. That is, stationary tags embedded into the receivers with known emission times. The argument sync_emissions tells kaltoa which emit_id values should be treated as sync-tag emissions. We have the supplementary type column to distinguish between the types of tags detected/emitted when multiple types of tags are used.