Monthly Archives: February 2014

An Inexpensive Tablet / GPS Configuration

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Introduction

In the process of adding some new tablet/GPS capabilities to RockWorks16, we decided to conduct a simple field test using a variety of devices (Figure 1).  This study is also part of an ongoing effort to establish an optimal low-cost cordless field configuration that we can recommend to RockWare customers.

GPS_01

Figure 1. Devices used in field test.

Methodology:

We started with a Dell Venue 8 Pro 64gb tablet PC ($319) running Windows 8.1 coupled with a wireless Wintec WBT-201 Bluetooth GPS ($95). The coupling between the Bluetooth antenna and the Windows 8.1 sensor array was facilitated by using the free GPS Sensor software (version 7.0.0.0.10) by Michael Chourdakis (http://www.turboirc.com).

The locations of three survey stations were measured via the aforementioned configuration along within the output from two consumer-grade GPS units; A Garmin Oregon 550t ($353) and a Garmin 60CSx ($500 but discontinued and replaced by $263 Garmin 62S).

Results:

The horizontal offsets (error) relative to the control points displayed within Google Earth Pro (Figure 2) imagery are summarized as follows;

  • Dell Internal Tablet Sensor (aGPS): Inoperative (no WiFi network to provide IP addresses)
  • Garmin 60CSx: 4.88 meters
  • Garmin 550T: 1.62 meters
  • Wintec WBT-201: 3.82 meters
GPS_02

Figure 2. GPS locations plotted within Google Earth Pro.

The vertical offsets (error) were not determined because the actual elevations at the control points are unknown to the author.

Conclusions:

  • The Garmin 550t provided the best results.
  • The convenience of the Wintec WBT-201 Bluetooth antenna (i.e. no cables and direct entry into the RockWorks16 datasheet without typing) is offset by the superior results from the Garmin 550t.
  • The Garmin 60CSx should be permanently retired.
  • Although the Dell Venue 8 Pro sensor array includes a tiltmeter, the lack of a digital compass (without WiFi access) renders is useless for dip-direction/dip-angle measurements. Sigh.

Suggestions For Future Study:

  • A high-end Trimble unit (~$13k) should be used to establish the validity of the control point coordinates.  The coordinates within this study were based on the questionable assumption that the imagery within Google Earth Pro has been accurately geo-rectified.
  • A low-end USB GPS antenna (e.g. $37 GlobalSat BU-353S4) should be incorporated into the next study.