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Improving the accuracy of estimates of animal path and travel distance using GPS drift ‐ corrected dead reckoning

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ABSTRACT

Route taken and distance travelled are important parameters for studies of animal locomotion. They are often measured using a collar equipped with GPS. Collar weight restrictions limit battery size, which leads to a compromise between collar operating life and GPS fix rate. In studies that rely on linear interpolation between intermittent GPS fixes, path tortuosity will often lead to inaccurate path and distance travelled estimates. Here, we investigate whether GPS‐corrected dead reckoning can improve the accuracy of localization and distance travelled estimates while maximizing collar operating life. Custom‐built tracking collars were deployed on nine freely exercising domestic dogs to collect high fix rate GPS data. Simulations were carried out to measure the extent to which combining accelerometer‐based speed and magnetometer heading estimates (dead reckoning) with low fix rate GPS drift correction could improve the accuracy of path and distance travelled estimates. In our study, median 2‐dimensional root‐mean‐squared (2D‐RMS) position error was between 158 and 463 m (median path length 16.43 km) and distance travelled was underestimated by between 30% and 64% when a GPS position fix was taken every 5 min. Dead reckoning with GPS drift correction (1 GPS fix every 5 min) reduced 2D‐RMS position error to between 15 and 38 m and distance travelled to between an underestimation of 2% and an overestimation of 5%. Achieving this accuracy from GPS alone would require approximately 12 fixes every minute and result in a battery life of approximately 11 days; dead reckoning reduces the number of fixes required, enabling a collar life of approximately 10 months. Our results are generally applicable to GPS‐based tracking studies of quadrupedal animals and could be applied to studies of energetics, behavioral ecology, and locomotion. This low‐cost approach overcomes the limitation of low fix rate GPS and enables the long‐term deployment of lightweight GPS collars.

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The effect of sampling frequency on 2D‐RMS position error, proportional accuracy, and collar battery life (GPS measurements only). (A) 2D‐RMS position error versus sampling fixes per hour. (B) Proportional accuracy for the domestic dogs versus sampling fixes per hour. Proportional accuracy (Dp) is the ratio of the true distance traveled (dt) to the apparent distance travelled (da) (Marcus Rowcliffe et al. 2012). Proportional accuracy varies between 0 and 1, with 1 being perfectly accurate. (C) Average collar current drawn. (D) Proportional accuracy for agouti (Marcus Rowcliffe et al. 2012), African wild dogs (Creel et al. 2013), and domestic dogs. (E) Collar battery life. Note the trade‐off between accurate position data and travel distance and collar battery life (A and E).
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ece32359-fig-0003: The effect of sampling frequency on 2D‐RMS position error, proportional accuracy, and collar battery life (GPS measurements only). (A) 2D‐RMS position error versus sampling fixes per hour. (B) Proportional accuracy for the domestic dogs versus sampling fixes per hour. Proportional accuracy (Dp) is the ratio of the true distance traveled (dt) to the apparent distance travelled (da) (Marcus Rowcliffe et al. 2012). Proportional accuracy varies between 0 and 1, with 1 being perfectly accurate. (C) Average collar current drawn. (D) Proportional accuracy for agouti (Marcus Rowcliffe et al. 2012), African wild dogs (Creel et al. 2013), and domestic dogs. (E) Collar battery life. Note the trade‐off between accurate position data and travel distance and collar battery life (A and E).

Mentions: The result of simulations and measurements to show the effect that GPS sampling frequency has on 2D‐RMS position error, proportional accuracy, collar current consumption, and battery life is shown in Figure 3A,B,C,E. At low sampling frequencies, between 2 and 12 fixes per hour, 2D‐RMS position error and proportional accuracy are poor (median 2D‐RMS >275 m and median Dp < 0.55, Fig. 3A,B), but the low current requirement (Fig. 3C) results in a long battery life of between 28 and 14 months (Fig. 3E). More accurate estimation of path and distance travelled (median 2D‐RMS < 8.37 m and median Dp > 0.88, Fig. 3A,B) requires GPS fix frequencies of greater than 720 fixes per hour (1 fix every 5 sec), but high current consumption (Fig. 3C) reduces collar battery life to approximately 1 week (Fig. 3E).


Improving the accuracy of estimates of animal path and travel distance using GPS drift ‐ corrected dead reckoning
The effect of sampling frequency on 2D‐RMS position error, proportional accuracy, and collar battery life (GPS measurements only). (A) 2D‐RMS position error versus sampling fixes per hour. (B) Proportional accuracy for the domestic dogs versus sampling fixes per hour. Proportional accuracy (Dp) is the ratio of the true distance traveled (dt) to the apparent distance travelled (da) (Marcus Rowcliffe et al. 2012). Proportional accuracy varies between 0 and 1, with 1 being perfectly accurate. (C) Average collar current drawn. (D) Proportional accuracy for agouti (Marcus Rowcliffe et al. 2012), African wild dogs (Creel et al. 2013), and domestic dogs. (E) Collar battery life. Note the trade‐off between accurate position data and travel distance and collar battery life (A and E).
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getmorefigures.php?uid=PMC5016644&req=5

ece32359-fig-0003: The effect of sampling frequency on 2D‐RMS position error, proportional accuracy, and collar battery life (GPS measurements only). (A) 2D‐RMS position error versus sampling fixes per hour. (B) Proportional accuracy for the domestic dogs versus sampling fixes per hour. Proportional accuracy (Dp) is the ratio of the true distance traveled (dt) to the apparent distance travelled (da) (Marcus Rowcliffe et al. 2012). Proportional accuracy varies between 0 and 1, with 1 being perfectly accurate. (C) Average collar current drawn. (D) Proportional accuracy for agouti (Marcus Rowcliffe et al. 2012), African wild dogs (Creel et al. 2013), and domestic dogs. (E) Collar battery life. Note the trade‐off between accurate position data and travel distance and collar battery life (A and E).
Mentions: The result of simulations and measurements to show the effect that GPS sampling frequency has on 2D‐RMS position error, proportional accuracy, collar current consumption, and battery life is shown in Figure 3A,B,C,E. At low sampling frequencies, between 2 and 12 fixes per hour, 2D‐RMS position error and proportional accuracy are poor (median 2D‐RMS >275 m and median Dp < 0.55, Fig. 3A,B), but the low current requirement (Fig. 3C) results in a long battery life of between 28 and 14 months (Fig. 3E). More accurate estimation of path and distance travelled (median 2D‐RMS < 8.37 m and median Dp > 0.88, Fig. 3A,B) requires GPS fix frequencies of greater than 720 fixes per hour (1 fix every 5 sec), but high current consumption (Fig. 3C) reduces collar battery life to approximately 1 week (Fig. 3E).

View Article: PubMed Central - PubMed

ABSTRACT

Route taken and distance travelled are important parameters for studies of animal locomotion. They are often measured using a collar equipped with GPS. Collar weight restrictions limit battery size, which leads to a compromise between collar operating life and GPS fix rate. In studies that rely on linear interpolation between intermittent GPS fixes, path tortuosity will often lead to inaccurate path and distance travelled estimates. Here, we investigate whether GPS&#8208;corrected dead reckoning can improve the accuracy of localization and distance travelled estimates while maximizing collar operating life. Custom&#8208;built tracking collars were deployed on nine freely exercising domestic dogs to collect high fix rate GPS data. Simulations were carried out to measure the extent to which combining accelerometer&#8208;based speed and magnetometer heading estimates (dead reckoning) with low fix rate GPS drift correction could improve the accuracy of path and distance travelled estimates. In our study, median 2&#8208;dimensional root&#8208;mean&#8208;squared (2D&#8208;RMS) position error was between 158 and 463&nbsp;m (median path length 16.43&nbsp;km) and distance travelled was underestimated by between 30% and 64% when a GPS position fix was taken every 5&nbsp;min. Dead reckoning with GPS drift correction (1 GPS fix every 5&nbsp;min) reduced 2D&#8208;RMS position error to between 15 and 38&nbsp;m and distance travelled to between an underestimation of 2% and an overestimation of 5%. Achieving this accuracy from GPS alone would require approximately 12 fixes every minute and result in a battery life of approximately 11&nbsp;days; dead reckoning reduces the number of fixes required, enabling a collar life of approximately 10&nbsp;months. Our results are generally applicable to GPS&#8208;based tracking studies of quadrupedal animals and could be applied to studies of energetics, behavioral ecology, and locomotion. This low&#8208;cost approach overcomes the limitation of low fix rate GPS and enables the long&#8208;term deployment of lightweight GPS collars.

No MeSH data available.


Related in: MedlinePlus