iPhone GPS reliability in general aviation - 2010

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Data

[PEREZGONZALEZ Jose D (2010²). iPhone GPS reliability in general aviation. Journal of Knowledge Advancement & Integration (ISSN 1177-4576), 2011, pages 5-6.] [Printer friendly]

iPhone GPS reliability

The reliability of the iPhone's GPS tracking feature was assessed empirically by Perezgonzalez in 2010¹. The research used an iPhone and a specialized tracking device (Spidertracks) on the same training flight. At the end of the flight, the data collected by both technologies were compared. More specifically, data regarding four flight parameters were correlated to assess the tracking variability of the two technologies. The results obtained are shown in the table below for each of the four flight parameters of interest.

Table 1. Variability assessment
flight parameter	Pearson coefficient	significance
Latitude	0.991	p < 0.000
Longitude	0.997	p < 0.000
Altitude	0.990	p < 0.000
Speed	0.927	p < 0.000

Methods

Sample and procedure

• 76 data points (time intervals) comprising data for two paired subsamples: data for Spidertracks, and data for iPhone (four variables each).
• Data points were collected from a single, one hour and seventeen minutes long flight. Both technologies were onboard a Piper PA-28-161 Warrior during a typical training session. No malfunctioning or other problems were found with the technologies, and non-technological variability did not affect the reliability of technology, either. Therefore, further measurements (in time or space) were deemed not necessary.
• The sample size was limited by the maximum number of data points recorded by Spidertracks (which tracked flight performance less frequently, or once per minute). The iPhone, instead, tracked flight performance per second. Thus, the corresponding 76 data points for the iPhone sample were selected by matching the first data points in the sequence for both technologies, and then collating the remaining data points spaced at regular intervals from the previous data point. Selecting the first data point from the iPhone database was approximate, using a triangulation of measures. Although some uncertainty may remain regarding this first matching, the remaining data points were selected objectively, at exactly one minute intervals from the first one.

Materials

• One Spidertracks unit (a commercial GPS fleet monitoring tracking device).
• One iPhone unit with a GPS flight tracking programme installed. The phone was used without its phone card.
• A stopwatch.

Data analysis

• The data matrix was assessed as per normality and linearity. Results were adequate for continuing with parametric data analysis.
• Main analyses were t-tests for paired-samples for the four variables under study.

References

References

1. PEREZGONZALEZ Jose D (2010). Reliability analysis of assisted-GPS technologies for post-flight analysis. Aviation Education and Research Proceedings (ISSN 1176-0729), volume 2010, pages 53-54.

+++ Footnotes +++

2. Reproduced with permission from PEREZGONZALEZ Jose D (2010). Assisted-GPS reliability. AviationKnowledge (ISSN 1179-6685), 2010, page 7.

Did you understand?

+ Test yourself

• 1- Spidertracks and iPhone seem to have similar GPS reliability
  • a- Yes, the probabilities of results are statistically significant, thus we can infer the high correlations are true.¹
  • b- No, correlations are low.²
  • c- No, the significance levels of correlations are low.³

Test answers

1. Correct, at least for the four variables in our study.

2. Incorrect, correlations are actually very high and, given the significance of the results, we can infer they are also true.

3. Incorrect, significance levels are adequate (sig<0.05), thus we can infer provisional support for the hypothesis that reliability is good.

Author

Jose D PEREZGONZALEZ (2010). Massey University, New Zealand (JDPerezgonzalez).

Peer-reviewers

Stuart ANDERSON (2010). School of Aviation, Massey University, New Zealand (stuartanderson).
Anthony FRYER (2010). School of Aviation, Massey University, New Zealand (Anthony Fryer).

Want to know more?

Perezgonzalez's (2010) article

The original article can be found under the "2010 Symposium Proceedings" tab, as PEREZGONZALEZ Jose D (2010). Reliability analysis of assisted-GPS technologies for post-flight analysis. Aviation Education and Research Proceedings (ISSN 1176-0729), volume 2010, pages 53-54.

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