A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Iwancio
Date: 2021 Jan 20, 22:23 -0800
Am I right in thinking that LoP's do not strictly cross intercepts at right angles?
Here's my train of thought. Please point out where I've jumped the rail.
- Plotting is typically done on Mercator projections (or something "close enough")
- A (small) circle on the earth's surface is still a circle on a Mercator chart (generally), i.e. they don't turn into ovals
- (I'm assuming a spherical earth without flattening)
- A great circle on a Mercator chart is not a straight line (generally)
- Intercepts are drawn from the AP along the great-circle direction towards the geographic point
- Because intercepts aren't "straight" (i.e. rhumb) lines on the Mercator chart, they aren't pointing "directly" at the center of the small circle
- Therefore, an intercept doesn't cross a line of position (an arc of a small circle) at a right angle (generally)
This would explain why some of the math of a project of mine isn't quite working out. I'm guessing it would be "more correct" to rotate the LoP slightly by an amount equal to the conversion angle.