A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2018 Nov 19, 03:46 -0800
One of the youth engagement activities we have used with the East Midlands Branch of the RIN when working with school children ages 7-15 for up to one hour is to copy Eratosthenes in calculating the circumference of the Earth but using two GNSS positions 80-100m apart depending upon space available along a meridian, the distance measured using a trundle wheel. (A little thought makes you realise this is a bit of a cheat and that results of around 1% accuracy are inevitable with a decent trundle wheel on good ground, but don’t tell the kids that). I soon found that it was best to set the GNSS receivers to d.ddddd and work solely in degrees. It wasn’t that the older, brighter students couldn’t work in degrees and minutes or degrees, minutes, and seconds, it simply saved valuable time revising what they’d learned in Maths and made it much easier to produce a simple worksheet.
I see that in 2000 the task for the Coordinate Systems & Map Projection Module of my part-time MSc was to calculate the difference in distance between London 51°30’N 000°05’W and New York 40°43’N 73°59’W using both spherical and ellipsoidal trigonometry. The results were: spherical 5,577.9km using radius 6,378,137m, ellipsoidal 5586.7km using WGS84. Anyway, the point is that at the time I didn’t even own a scientific calculator, so I bought the cheapest and was too lazy to check if I it would work in d,m,s. I found it much easier to turn the coordinates into just d.dddddd and reconvert to d,m,s for the bearings between start and finish points, which were also required. I also see that surprisingly I received maximum marks, but I’m afraid to say that eighteen years later I can barely understand a line of my working. DaveP