A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2019 Nov 24, 11:06 -0800
Have you tried my GPS Anti Spoof app yet? It's primarily intended as a celestial test to detect GPS Spoofing, but under conditions where you're not worried about spoofing, it's an excellent fast test of your sextant sights. Great for beginners but also useful for experienced observers who just want to see how well they're doing or want to test results under varying horizon conditions like with those "floating islands" that you've seen. The app tells you exactly what your sextant should read from your location, no calculations, no paperwork. Any difference between the display and your observatiojn is your error (or equivalently your intercept from the GPS position as AP).
From my website:
Get my new app. Defeats GPS Spoofing and great for sight-training, too: instant feedback with no paperwork at all. There's a standard version (free on Android, inexpensive on iPhone/iPad) that works with Sun, Venus, and Polaris sights and can function for three to seven days without network access. If you're serious about your navigation, then get the PRO version which includes the Sun, Moon, Venus, Mars, Jupiter, Saturn, Polaris and all 57 standard "navigational stars" and works offshore and off-network for months at a time.