A ridiculous proof of concept: xyz interpolation

March 14, 2012

(This article was first published on me nugget, and kindly contributed to R-bloggers)

Ridiculous Orb

This is really the last one on this theme for a while… I had alluded to a combination of methods regarding xyz interpolation at the end of my last post and wanted to demonstrate this in a final example.

The ridiculousness that you see above involved two interpolation steps. First, a thin plate spline interpolation ("Tps" function of the fields package) is applied to the original random xyz field of distance to Mecca. This fitted model is then used to predict values at a new grid of 2° resolution. Finally, in order to avoid plotting polygons for each grid (which can be slow for fine grids), I obtain their projected coordinates with the mapproject function. Using these projected coordinates and their respective z values, a second interpolation is done with the "interp" function of the akima package onto a relatively fine grid of 1000×1000 positions. The result is a smooth field that can then be overlayed on the map using the "image" function (very fast).

So you may ask – When is this even necessary? I would say that it really only makes sense for projecting a filled.contour-type plot for relatively sparse geographic data. Be warned – for large amounts of xyz data, the interpolation algorithms can take a long time.

A couple of functions, found within this blog, are needed to reproduce the plot (earth.dist, color.palette).

the code to reproduce the figure…
Read more »

To leave a comment for the author, please follow the link and comment on their blog: me nugget.

R-bloggers.com offers daily e-mail updates about R news and tutorials on topics such as: Data science, Big Data, R jobs, visualization (ggplot2, Boxplots, maps, animation), programming (RStudio, Sweave, LaTeX, SQL, Eclipse, git, hadoop, Web Scraping) statistics (regression, PCA, time series, trading) and more...

If you got this far, why not subscribe for updates from the site? Choose your flavor: e-mail, twitter, RSS, or facebook...

Comments are closed.


Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)