location quiz

[Jack E]

In Ralphs location quiz a few people gave the correct answer of using triangulation to find a position.

Can anyone give a description of the triangulation method?

[Wood Borer]

A triangle is used because it's shape and size is fixed if you have any of the following.

2 angles & 1 side

1 angle & 2 sides (can define 2 triangles)

3 sides

The 2 angles and 1 side is often used in triangulation with the known side being referred to as the base line.

I have used this method when navigating a yacht to calculate your distance off shore by taking a bearing off a known point such as a lighthouse, sailing a fixed distance and course and then taking a bearing off the lighthouse again. This is called a running fix. The known side is the distance sailed and the two angles are calculated from the two bearings.

A simpler method is to take a bearing off two known points whilst in the same position. The known side is the distance between the objects and the two angles are calculated from the bearings.

These days people use GPS units and drown when the GPS stops working. As a non swimmer I learnt to use all sorts of methods of navigation.

- Wood Borer

[bitingmidge]

It's all to do with the square root of the sum of the opposite sides!

Apparently.

P
If God had meant us to swim he wouldn't have given us boats.

[Wood Borer]

That's true Bitingmidge but only for right angled triangles. I have studied a bit of trigonometry but you don’t need to use these theories when navigating, you just draw the lines on the charts.

Using triangles saves you going around in circles but if you stuff up the calculations it can send you around the bend!

- Wood Borer

[bitingmidge]

Navigating at sea is something I take rather seriously, although like everything else in life it can be broken down into small parts to make it easier to chew.

I am sure it was the truly great navigator Sir Francis Chichester who said "Crossing Oceans is easy, it's just the hard bits round the edges that you have to watch out for".

If he didn't say it, he should have!


Cheers,

P

[Ivan in Oz]

I have studied a bit of trigonometry but you don’t need to use these theories when navigating, you just draw the lines on the charts.

- Wood Borer

WB,

I used to draw lines on paper [and everything else when I was at Kindy]
BUT they were curved lines.

Is that why I went around in circles and got nowhere?

Count

[Wood Borer]

Ivan,

Straight lines are only a theory, they hardly ever occur naturally, even light bends when it goes past planets and other heavenly bodies

Perhaps you were on the straight and narrow when you were drawing curves, either that or you were advanced and dreaming of other heavenly bodies that the rest of us discovered later in life.

- Wood Borer

[bitingmidge]

In fact the straightest line to anywhere on earth is a curve.

The easiest way to explain this is to slice an orange into four and peel it.

Flatten a peel quadrant, firstly you'll see what was once straight line (cut) is now an arc, so the shortest dimension to the top and bottom is a straight line between them....it was once where the cut was ...how can this be???

Now draw two dots about a quarter of the way from the top and bottom on the edge of one of the cuts, and draw a straight line connecting the two (with the skin still flat). That is the shortest path between the two points inarguably.

Now put the peel back on the orange so that it resumes it's original spherical profile, and you should see that the straight line has developed a curve!!

I don't know how understandable that is, but racing yacht navigators have complicated formulae to build in this correction over long distances.....pilots probably do to???

Curious stuff.

Ralph needs a question on this I think.

P

[Wood Borer]

It is called Great Circle navigation but it only applies over large distances. I was only involved in cruising in Bass Strait not racing but as the distances in Bass Strait are relatively small (100's of Nautical miles) I never bothered with these calculations. It might have saved me 1 mile - so what when the helmsman is flat out keeping to within 10 degrees of the course.

A Great Circle is the path represented if you placed a piece of string on the surface of the earth between the points and pulled it tight. If you are going great distances especially if you were racing then Great Circle navigation would be an advantage. Other factors need to be taken into account such as favourable currents and winds.

Rhumb lines are straight lines drawn on a chart with mercator projections. Charts are flat representations of our curved planet so in reality they turn out to be curves even though they are straight on the chart.

Might be able to incorporate these ideas into furniture design or maybe the turners use these ideas with their curved masterpieces.

- Wood Borer

[bitingmidge]

Might be able to incorporate these ideas into furniture design or maybe the turners use these ideas with their curved masterpieces.

Sort of "the doors are edged in Rhumb lines with hinges of projecting mercator, finished by leaving in wafted unfavourable winds after drinking a whole can of WD40."

I can see it catching on in Vogue Living as we speak!

(I hope you're writing all this down Jack!)

Cheers,
P

[Jack E]

OK, I will start you off,

You can see three prominent features which you can relate to the map, you then take a bearing to said features.

What do you do to these bearings and how do you use them to find your position?

[Wood Borer]

Jack,

you only need 2 points but three will give you a more accurate position. Theoretically all three lines will intersect at the same point but in practice you will end up with a small triangle due to minor errors. Small triangle is called a "cocked hat".

How do you do it?

Let's say you take the following bearings with your compass from your unknown position.

Point A 300 degrees, Point B 030 degrees and Point C 045 degrees.

Add or subtract 180 degrees from each of these points so now you end up with 120, 210, and 225 respectively. It doesn't matter if you add or subtract.

From point A draw a line with bearing 120 degrees, from point B draw a line with bearing 210 degrees and from point C 225 degrees. Where they intersect that's where you are.

- Wood Borer

[ozwinner]

Gees, Ill never be lost again, mind you I am very rarely lost.

Most people tell me where to go!!

Al

[Bob Willson]

In fact the straightest line to anywhere on earth is a curve.

Not quite correct biting, it is just that we humans have trouble navigating our way through solid rock.

[ozwinner]

In fact the straightest line to anywhere on earth is a curve.

Ive always thought this, when I use my laser at work, it must follow the curve of the earth.

Is this correct or not??
Or is it level, and is level, really level?
Lakes are level, and must follow the curve?

OK Ive confused even myself.

Al :confused: