Hello,
On 15-09-10 22:47, James Stegen wrote:
Hello, I have lat-long coordinates for a bunch of localities spread across multiple hemispheres, which also extend into high latitudes.
That's two hemispheres max, right?
What I would like to do is re-project the lat long coordinates into a projection that gives me spatial positions in km from some arbitrary point. The key is that I would like the distances among communities to be maintained.Specifically, if I calculate a distance matrix using lat longs in the great circle equation, I would like a distance matrix calculated from the reprojected positions to give the same distances.
That sets the requirements of the projection to equidistant, conformal and equal-area. If you read up on projections, even if it is on wikipedia, you will soon see that it can't be done. To be precise, it is possible in cases with less than three communities.
I haven't found a projection that can do this. Using the orthographic projection, for example, leads to larger distances among sites that occur at high latitudes, relative to the distances provided by the great circle equation. I also need to know actual spatial positions in both axes, not just overall distance, relative to an arbitrary point on earth.
Hth, Arien
Many Thanks, James Stegen
-- Arien Lam _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
