Magnetic Compass

[facthunter]

What's wrong with sighting a distinctive feature that is on your required planned track and forget about fences roads etc set a heading that has you tracking over it. and keep on doing that.?. I like to have a powerline or rail line. that must be kept a certain side of as a backup. Rivers are harder to identify positively. A "FIX you aren't certain of is not a fix.. You often want it to be some thing so you misguide your self into making it so. Nev

[antonts]

Be they magnetic or true.

 

land surveyors, mine marksheiders, construction engineers etc always use TRUE direction - all maps are in TRUE, as in TRUE there is no need for any correction with position and time, and it works even if you do not have any earth magnet field at all like in deep underground mine surrounded with iron ore. For more than 100 years everybody uses gyrocompass, not as we all know on planes, but ground-linked, with weight pointing down by gravity and self-alighning with Earth rotation vector (axle). Very simple device, but it allows precision up to centimeters in several kilometers of underground tunneling.

[pmccarthy]

Old time surveys can be very accurate. Back in the 19th century they could close a survey traverse of several miles within an inch or so. All based on true grid, you then just adjust for magnetic variation.

[Old Koreelah]

What's wrong with sighting a distinctive feature that is on your required planned track and forget about fences roads etc set a heading that has you tracking over it. and keep on doing that.?. I like to have a powerline or rail line. that must be kept a certain side of as a backup. Rivers are harder to identify positively. A "FIX you aren't certain of is not a fix.. You often want it to be some thing so you misguide your self into making it so. Nev

Yes Nev, it's possible to line up your aircraft with a distant point, if you know it's exact bearing.

Surveyed property boundaries are so much easier to use, because they go for miles and are available in almost all settled areas. Many such fence lines clearly show Cardinal directions and are very easy to see, because of abrupt vegatation changes.

[Old Koreelah]

Old time surveys can be very accurate. Back in the 19th century they could close a survey traverse of several miles within an inch or so. All based on true grid, you then just adjust for magnetic variation.

One of the most impressive British surveying feats involved finding the height of the recently-discovered Mt. Everest; two teams started from sea level, either side of India and spent years setting up scores of Trig stations across the subcontinent until they were in sight of the great mountain. I can't find a map of their survey, but it looks like the Sydney Harbour Bridge. Using this exhausting method, they came within a poofteenth of what the latest laser technology arrived at.

 

https://media.nationalgeographic.org/assets/file/TWD_Measuring_Mount_Everest.pdf

[flying dog]

land surveyors, mine marksheiders, construction engineers etc always use TRUE direction - all maps are in TRUE, as in TRUE there is no need for any correction with position and time, and it works even if you do not have any earth magnet field at all like in deep underground mine surrounded with iron ore. For more than 100 years everybody uses gyrocompass, not as we all know on planes, but ground-linked, with weight pointing down by gravity and self-alighning with Earth rotation vector (axle). Very simple device, but it allows precision up to centimeters in several kilometers of underground tunneling.

 

Yeah, ok, sorry.

 

Got ahead of myself a bit.

[facthunter]

Of course you can't use magnetic on maps. It just wouldn't work on a CHART. MAPs are very confusing as you cant make spherical surfaces represent accurately on a flat one. The shortest distance between any two points is a great circle, the "plane" of which must pass through the earths centre. IF you fly a constant true heading other than the obvious exceptions the equator and any North south track you won't fly a great circle.. nor will you have a constant lat or long scale to angle change. Nev