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! :D

- 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 :D

[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. :D

[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:

[Eastie]

Gravity will pull your laser into level with the curve of the earth Oz, that's why standards and tolerances allow you a few mm here and there ;)

PS. Something that I've always been astounded with is the lurnar method for measruing longitude - and the ability of early sailors in using it without a watch :confused:

[Jack E]

Very close Woodborer,

You forgot to take into account the magnetic variation applicable to the particular map being used.
The bearings taken with the compass are magnetic bearings but before you plot them on your map you must convert them to grid bearings (either before or after you add or subtract 180 degrees).
This is because magnetic north, true north and grid north are all different and the variation must be considered.
Magnetic variation will be shown on the map and will be correct for a certain year, usually the date of survey. The variation will change, usually annually or bi annually and must be multiplied by the difference in years between when the map was correct and the year you are geographically embarressed.
To convert from a magnetic bearing(one taken with a compass) to a grid bearing(one plotted on a map) you add the variation. To convert from a grid bearing to a magnetic bearing you subtract the variation.
These conversions are for a map with an easterly variation(which will also be shown on the map) and you simply do the opposite for a map with a westerly variation.

[Wood Borer]

Eastie I think you didn't understand Dr Ozwinner's statement.

He uses a laser to put people on the level whilst performing his brain surgery. The dimensions would be neurons not mm.

- Wood Borer

[Wood Borer]

Jack,

You are quite correct if your compass reads magnetic but most good compasses read true. You can change the variation on them so they read true.

I have a handheld Suunto compass that I have calibrated for true in these parts (approx 11 degrees East). Mine is also designed for the Southern Hemisphere for the Australian region this keeps the needle almost horizontal instead of dipping.

On the yacht we had a fluxgate compass which I adjusted for both variation and deviation which made the calculations a bit simpler especially in rough seas when you are half asleep.

It sounds like you already knew how to do determine your position using a compass when you asked the question.

- Wood Borer

[Bob Willson]

Gravity will pull your laser into level with the curve of the earth Oz, that's why standards and tolerances allow you a few mm here and there ;)Sorry Eastie, I can't make out whether you are meant to be joking here or not. :confused:

[ozwinner]

Sorry Eastie, I can't make out whether you are meant to be joking here or not. :confused:
Psst Bob.
Easties gone to the great cat killing field in the sky, remember? :(

Al

[DavidG]

The beam of a laser does not follow the curvature of the earth and given ideal conditions will remain straight whilst the earth gradually falls away below it.
Unfortunatly for lasers they are badly effected by refraction in the air.
When two layers of air of different temperature meet the interface between the air masses acts as a lens and bends the laser beam.

This can be seen on a hot day as a shimmering in the air.

As any big bore shooter would know, the effect can be quite large over a longer range with errors between apparent and the real location of the target being measured in +-metres over 1000m range.

[Jack E]

Wood borer,
I wish I had an adjustable compass instead of the old prismatic from WWII, that would make life much easier!
I did know the answer to the question. It would be silly of me to post a question on a QUIZ thread if I didn't know the answer myself.
Jack.

[journeyman Mick]

Just a little bit of trivia, slightly off topic (but prompted by the laser levels and earth's curvature).
The two towers of the Golden Gate Bridge (largest suspension bridge in the world) are perfectly plumb but are not parallel. Because they are so far apart and so tall the curvature of the earth means that they lean away from each other whilst being perfectly plumb. (Hint to Al, use this as an excuse next time something's out of whack :p :D )

Mick the trivia master :rolleyes:

[Wood Borer]

So Mick the leaning tower of Pisa is vertical but just not at the place where it is located.

Your theory (which I understand and agree with) suggests that buildings should be wider at the top than at the base if the walls are vertical. The top floor would therefore have a larger area than the ground floor.

Is this why people pay more for penthouses than basements? :D

Perhaps Al takes this into account when quoting on jobs.

- Wood Borer