Tru-Path

Row, row, row your boat gently up / down the stream???

Purpose: This blog is created to help readers a) better understand electronic compass [smartphone or rangefinder] residual azimuth deviation errors b) quantify the errors, c) model the errors, d) compensate for [correct] the errors, and e) influence the app vendors to apply the correction method within the affected smartphone app. Basically, we need to know (accurately) whether to go up / down the stream (path) we are traveling on.

Background: Case Study 10

This post will present the test results (accuracy & reliability) of the Android (Samsung S23-Ultra) smartphone & Jerusalem Compass app operated at the Birmingham, AL test site within a strong magnetic/electromagnetic field. 

The primary feature of the Jerusalem Compass app is to point the user (from the user’s then-current geographic location) toward the Temple in Jerusalem, Israel. The geographic coordinates of the Temple in Jerusalem are:

• Latitude: 31.77765N
• Longitude: 35.23547E

The Jerusalem Compass app user located in Birmingham, AL would be pointed in a direction 46.38 degrees east of True North – assuming that the Jerusalem Compass was actually correct in establishing the True North direction.

The test results from this case study clearly demonstrate that residual (after calibration) compass azimuth deviation error exists and that residual deviation error can be effectively corrected (compensated).

The Birmingham, AL test site is set in an urban environment with strong magnetic/electromagnetic influences including:

• An electric power distribution station for eight (8) townhomes
• At least eight operating heating/cooling (heat pump) units of 3 to 4 ton capacity – aligned North/South within 50 feet of the test site (East side)
• An active highway – aligned North/South within 150 feet of the test site (West side)

The data collection equipment and procedures used for this test (Android & Jerusalem Compass) were identical to those used at the Birmingham, AL test site for all prior posts.  Refer to the original post/page: “http://www.tru-path.org”

• True North (reference direction) was established based on the sun position relative to the test site’s geographic location on the date/time of the test – a correct, defendable, and independent reference direction.
• The Android compass was set to indicate azimuths relative to True North.
• The Android phone (Samsung S23-Ultra) compass was re-calibrated prior to this test.
• The Android phone was mounted on a tripod equipped with an indexed compass ring – used to ensure the correct principal directions were achieved prior to taking the actual measurements. Therefore, no “sighting” errors were experienced during data capture operations.

Test Results

Recall: Residual (after calibration) compass deviation error persists throughout the entire 360 degree range of measurement.  The following data table presents the collected azimuth data (yellow) and the associated deviation error (orange) for three Android phone orientations (horizontal, portrait, and landscape). The compass deviation error data was collected in the same manner as all the other error data presented in this blog series.

Notice that the azimuth deviation (error) is different for each orientation of the Android phone.  The Jerusalem Compass app has done its best – yet residual compass azimuth deviation (error) persist.

The “modeled” deviation curves (derived from the residual deviation error) for the Android & Jerusalem Compass app are presented below.  The modeled residual azimuth deviation compensation curves are presented in two different formats to allow the reader to seriously consider the deviation error – as measured throughout the full 360 degree range of measurement.

The compensated deviation errors (remaining azimuth errors after compensation) for the Android & Jerusalem Compass app are depicted below.  Again, two display formats are provided to strengthen the perceived impact of the compensation method.

The predicted deviation errors for the Android & Jerusalem Compass app are depicted in the following chart.  The predicted error curves are the negative of the deviation curves; and the compensation method proved quite effective.

Conclusions:

• The Android & Jerusalem Compass app indicate the following error ranges, within a 95% confidence limit: +3.4 < Horizontal < +11.1 / +15.5 < Portrait < +23.8 / +11.2 < Landscape < +21.6 degrees.
• The Android & Jerusalem Compass app is inaccurate and unreliable to determine the correct direction in all cases – especially in the Portrait orientation.
• The residual compass azimuth deviation error compensation method used in this test (research) is quite effective in compensating the residual deviation error experienced.

Preview: In upcoming blog posts, we will continue to deal with other Android and iOS compass apps – as well as with laser rangefinders with a compass. As with previous tests the same methods will be used to collect, analyze, and present the results.