Having recently received a comment on a post regarding geographic xyz data interpolation, I decided to return to my original "xyz.map" function and open it up for easier interpretation. This should make the method easier to adapt and follow.
The above graph shows the distance to Mecca as interpolated from 1000 randomly generated lat/lon data using the "interp" function of the akima package. Several functions, found within this blog, are needed to reproduce the plot (pos2coord, earth.dist, new.lon.lat, color.palette, val2col, image.scale). One thing you will notice is the strip of uninterpolated area within the stereographic projection. This is a problem that I have yet to resolve and has to do with the fact that the interpolation is not considering the connection along the 180° longitude line. This will probably require some other type of interpolation based on geographic distances rather than Cartesian coordinates.
R code to produce the above graph...
