>> >> 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. >> >> Yup, the z coordinate is wrong. Only the x and y are right. >> >> Peter >> > > I believe that should have been mean(z)/2
mean(z)/2 isn't correct either. The correct answer it is the weighted mean of the center of mass coordinate of each column (which is z/2), and the weight (mass of the columns) is also z, that is the result is zCenter = 0.5 * sum(z^2)/sum(z) Apologies for the wrong formula for the cm coordinate z. Peter ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
