A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2017 Apr 3, 03:33 -0700
For my sight practices I chose a spot on the beach. So to be able to judge the quality of my LoPs, intercepts and fixes I decided to first obtain its' position by means of GPS.
A device that I used is a car navigation receiver that is able to show the position data in ddd.dddddd° format.
As I wondered to and fro around the spot - I could see that the LSDs (the least significant digits) were changing accordingly. But they never returned to exactly same values that the device settled to after capturing signals from 14 of 16 available satellites. The last xxx.xxxxdd were always +/-10~15 different - on the very same geographical position.
Also, while being at approximately 2 meters above the sea level - the device displayed rather different height: from reasonable 2.10m up to almost 6 meters - all with the same fourteen satellites received.
Am I asking too much from this toy-receiver? The arc-second is approximately 30 meters of distance, is it reasonable to expect the reliable fractions of arc-seconds values?
The Ho I got from my sight put me 5,2 miles off from Hc - I was taking a sight with the short dip for which I did not have the proper correction table.