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Hi Lois & All, Feb 11, 2007
That is slick. Being gadget oriented these days one tends to forget
the power of geometry (earth measurement).
Note that the angle OAD need not be a right angle, the only constraints
being that OA and GE be parallel and the ratio of DE to AD be known.I
would guess that, for given length of AD, error will be minimum when ODE
is 90o.
Yt, DW
Lois Codling wrote:
> Hi Jamie,
>
> My husband, Don, sends you the following suggestion:
>
> Many years ago, Ernest Thomas Seton published, in “Two little savages”
> a very simple means of measuring the distance to a remote object,
> using nothing but a few stakes, a string and a tape measure. It
> requires producing what in Geometry are called congruent triangles.
> you make a small triangle you can measure that matches a large one
> which you can’t measure, and easily get your distance.
>
> 1. Pick a visible point on the shoreline and call it O
> 2. Place a stake beside your house (call this A)
> 3. Place a stake (B) 4 m from A, directly in line with O (ABO is a
> straight line)
> 4. Establish a right angle to that line
> a. Tie your string to B, measure a 5 m length & use this to mark an
> ark in the area around a right angle to the line AB
> b. Tie your string to A, measure a 3 m length & use this to mark an
> ark which crosses the previous arc. Put stake C in the intersection.
> c. The line AC is at right angles to AB
> 5. Measure from A 30 m along the line AC and put in a stake D. ACD
> should be in a straight line.
> 6. Measure from D a further 3 m in the same line and put in stake E.
> ACDE should form a straight line (note that DE is 1/10 of the length
> of AD)
> 7. At E mark a right angle to the line ACDE, in the direction away
> from O, in the same way you established the right angle at A
> a. Tie your string to E, measure a 4 m length and mark an arc
> approximately where the right angle line will come
> b. Tie your string to D, measure a 5' length, and mark an arc crossing
> the previous arc. Put a stake F at the intersection
> c. The line EF is at right angles to the line ACDE
> 8. Extend that line to a point at which you can sight over the stake D
> directly towards O
> a. Insert a stake G at that point. GDO should be in a straight line.
> b. Measure from G to E
> c. The distance A to O is exactly 10 x the distance from G to E (or as
> exactly as your measurements and stake placements allow).
>
> Lois Codling
>
>
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