Pabrides
In surveying and to a certain extent in advanced navigation bearings are often given with a reference direction, a number of degrees, and a direction to sweep.
For example: N 30° W spoken as “North thirty degrees west.”
This tells you to start at North and sweep thirty degrees to the westward. That would be the same as a true compass bearing of 330° because (360° – 30°) = 330°
The prefix is the reference direction and the suffix is the direction in which to sweep.
In southern latitudes where the south pole is elevated you very well may come to a solution for a bearing, course, or azimuth taken from the south pole. In that case you might see it expressed as something like S 50° E which tells you to start from true south and to sweep eastward 50 degrees. This is a true compass bearing of 130° since (180° – 50°) = 130°
In surveying I am led to believe, though I'm not a surveyor, that the reference direction can be any of the four cardinal points. Those are North, East, South, and West. So if you were to see a call out on a survey of E 10° N that would be a true compass direction of 80° because (90° – 10°) = 80°
In navigation we generally only use North and South as reference directions with one exception: That is when taking the bearing to a rising or setting body used to check our compasses. Usually this body is the sun, and the bearing is taken at sunrise or sunset. It is referenced to East at sunrise and West at sunset and in this special case it is no longer called a bearing but instead an amplitude. A sun amplitude of W 08° N tells you that the sun set (because W is the reference direction) 08° northward of true West. This is 270° + 8° = 278° true.
This method of prefixing with the reference direction and suffixing with the sweep direction is exactly like the “by” points on the old compass rose. The reference direction precedes the “by” while the sweep direction follows the “by.”
“West by south” starts at West and sweeps a little Southward.
“Northwest by north” starts at northwest and sweeps a little northward.
And “South by southwest” can't be a compass point at all, but rather a music and film festival held in Austin Texas!
I never could remember how those pesky "by" points went until I read your older post today and it all fell together for me. Now I don't know how I could have missed it!
Thanks!
PeterB
In surveying and to a certain extent in advanced navigation bearings are often given with a reference direction, a number of degrees, and a direction to sweep.
For example: N 30° W spoken as “North thirty degrees west.”
This tells you to start at North and sweep thirty degrees to the westward. That would be the same as a true compass bearing of 330° because (360° – 30°) = 330°
The prefix is the reference direction and the suffix is the direction in which to sweep.
In southern latitudes where the south pole is elevated you very well may come to a solution for a bearing, course, or azimuth taken from the south pole. In that case you might see it expressed as something like S 50° E which tells you to start from true south and to sweep eastward 50 degrees. This is a true compass bearing of 130° since (180° – 50°) = 130°
In surveying I am led to believe, though I'm not a surveyor, that the reference direction can be any of the four cardinal points. Those are North, East, South, and West. So if you were to see a call out on a survey of E 10° N that would be a true compass direction of 80° because (90° – 10°) = 80°
In navigation we generally only use North and South as reference directions with one exception: That is when taking the bearing to a rising or setting body used to check our compasses. Usually this body is the sun, and the bearing is taken at sunrise or sunset. It is referenced to East at sunrise and West at sunset and in this special case it is no longer called a bearing but instead an amplitude. A sun amplitude of W 08° N tells you that the sun set (because W is the reference direction) 08° northward of true West. This is 270° + 8° = 278° true.
This method of prefixing with the reference direction and suffixing with the sweep direction is exactly like the “by” points on the old compass rose. The reference direction precedes the “by” while the sweep direction follows the “by.”
“West by south” starts at West and sweeps a little Southward.
“Northwest by north” starts at northwest and sweeps a little northward.
And “South by southwest” can't be a compass point at all, but rather a music and film festival held in Austin Texas!
I never could remember how those pesky "by" points went until I read your older post today and it all fell together for me. Now I don't know how I could have missed it!
Thanks!
PeterB