From: Lewis Jardine (firstname.lastname@example.org)
Date: Thu 08 May 1997 - 17:41:30 EEST
> Please, all who believe two compasses are not enough do this :
I'm one of them (still)!
> 1.Take a map of Glorantha (or a piece of paper) and mark two point A an=
d B on it.
Yes, I've done this in my previous post. =
> 2.Now determine what direction compass A and B point to.
Relative to what? =
This I believe is the crux of the problem. You appear to think that =
just because you have a map you know which way up it should be...
The normal way people use a map is to use a (single) compass to find =
magnetic north and then orient their map using this bearing. =
They then look for two prominant features and take bearings on =
them (relative to magnetic north) and find the intersection. =
This is why people keep coming back to the point about the angle =
between the two compasses. That is the angle of one needle relative =
to the other one which is something you can determine. =
> 3.Draw a line through point A with the same direction as the compass sh=
> 4.Do the same with compass B.
Again how? I don't know how to orient the map. =
> 5.Your lines meet in one point, this is the point where the two
> compasses show your before determined directions. =
> For those who know something about vectors :
> The two directions of the compasses can be seen as two different vector=
I believe that vectors also have a magnitude property, yours only have
I agree that if you knew the magnitude you could find your position, but
has been no discussion any valid methods to obtain this (actually, with
just 2 =
magnitudes you can narrow your position down to two possible locations =
(intersection of 2 circles). =
> With the point A and B you can make both lines. =
Hey, I thought we were talking about vectors? =
They are not tied to one location (unlike a line). =
> In a plane two different lines define one exact point !
> You can only measure the angle between the compasses ? NO! What you
> absolutely don't need is the angle, you need the directions. And they
> are absolute, =
Only if you can measure them relative to some fixed datum (like magnetic
> since they are the same in the same place. =
> Even if you turn 180=B0 they stay the same (Please do the little exerci=
If you are hodling the map firmly, =
the needle points in the same (absolute) direction, =
however the map turns with you, now your method places you =
on the opposite side of the point! =
> Again, this works only if you have a map.
The map is completely irrelevant to this discussion as it does not help
All you are using is a plain piece of paper with two points marked a
(scaled) distance appart. =
If you were using the map to sight on another fixed point I would
However, the maths involved would still be non-trivial as it would still =
be very difficult (maths) to calculate the return-bearing from the
> I hope I have not to post that often as I had to say that Telmori are n=
> chaotics !
Only if you persist in this line of arguement. =
Please see my previous post for a mathematical demonstration, =
which could be turned into a rigorous proof with a little effort. =
PS> I'll be at the German Glorantha Con if you wish to tackle me about
this issue there.
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