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Fred,
I afraid the method you propose is not practical. It is impossible to
measure your elevation in this way.

> If you could measure the angular distance between the islands you are
> viewing, knowing their true distance apart from the chart, you could
> compute your distance from the islands, that would be the hypotenuse
> of a right triangle.  The distance you measure on your chart would be
> the base of the right triangle.  Your elevation would be the height.
> The accuracy of this would depend on how accurately you measure the
> angular distance and the distances involved.

To do what you propose, you have to compute arccosine of something
which is close to 1.
And computing a small angle from its arccosine
is impossible.
Indeed, suppose the horizontal distance is 2 km, and
the elevation is 20 m. Then the hypotenuse is 2000.4 meters,
very nearly:-)
And if the elevation is zero, the hypotenuse is 2000 meters,
of course. So you need to measure the hypotenuse with ENORMOUS
precision (to centimeters!) to get your elevation, which is impossible.

Indeed, your elevation in the above example changes the distance only
by 40 centimeters.

Alex.

   

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