[R] Centre of gravity of a mountain

[Barry Rowlingson]

On Mon, Nov 8, 2010 at 5:15 PM, Peter Langfelder
<peter.langfelder at gmail.com> wrote:

> If you also need the z coordinate, it simply the mean of the matrix Z.
>
> zCenter = mean(Z)

 How can that be right? Suppose your mountain is very flat, so that
your mountain is effectively a cube. The Z values are all the same,
and so their mean is the same. However the centre of mass is, by
symmetry, clearly at height/2.

 Similarly suppose your mountain matrix is one large cell value and
all the rest are near zero - the mean Z will be close to zero but the
centre of mass will be almost half way up the single cell value,
because all the near-zeros contribute nothing to the centre of mass
position.


Barry