Position by Reciprocal Bearing

Today was a gorgeous day and I followed the usual cycle trek from my home QTH out to the Humber Bay and back along the Toronto Lakeshore. Sheldon Lookout is approximately at the half way point just over the cycle bridge and there I compared readings taken on my Silva Ranger Compass, my iPhone10 and Garmin GPS38. From years of field experience I have learned it’s always better to have two sets of measurements from different equipment saying more or less the same thing!

BearingSilva Ranger CompassiPhone10 Compass
Lake Shore Windmill91deg (91degGE)
271deg (reciprocal)
W.Toronto Island106deg (108degGE)107deg
H.Bay Shores Point169deg (168degGE)
349deg (reciprocal)
Table 1 Bearings Taken with Silva Ranger Hand Compass and iPhone10

The bearings were very similar on both the Silva and iPhone, although it is easier to sight with the Silva so the results are slightly better. The real results are taken off Google Earth and shown as red lines below. Note that with a hand bearing compass the best result obtained is usually several degrees out (must compensate for magnetic variation first). After taking the bearings, I measured the Latitude & Longitude on my older Garmin GPS38 (circa 1990s) vs. the iPhone10. The GPS38 took about 15 minutes to auto locate the ephemeris since I had not used it since last year. Finally it locked on 5 satellites in 3DNAV mode, with EPE22m. Lat & Long for both units were identical and within 20m of the exact location.

Fig.1 Bearings Taken from Sheldon Lookout
Garmin GPS38
Table 2 Position from GarminGPS38 vs. iPhone10

Now to get an estimate of my position, I used the Silva reciprocal bearings from Humber Bay Shores (169deg + 180deg = 349deg) & the Windmill ( 91 + 180 = 271deg). This is shown in Figure 2. The two bearings are optimal in that they are perpendicular to each other. The bearing position is about 50m from the actual position.

Fig.2 Position by Reciprocal Bearings HBShores=349deg & Windmill 271deg
Fig.3 Close Up of Actual Position and RB Position
Position by Reciprocal Bearings YouTube Video

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