[R-sig-Geo] Distance to (nearest) polygon

[Karl Ove Hufthammer]

On Tue, 26 Jan 2010 16:27:23 +0100 (CET) Roger Bivand 
<Roger.Bivand at nhh.no> wrote:

>> For example, I need the distance between points at sea to the nearest
>> land area (as defined by for example the 'world' dataset).
> 
> There are methods for point to line segment distances in spatstat. 
> Further, for projected (planar) coordinates, this could be added to 
> R-Forge rgeos; for geographical coordinates Boost ggl would be needed.
 
Thanks. The 'nncross' function in 'spatstat' does essentially do what I 
need. Unfortunately, I work with geographical coordinates (spanning 
about 15 degrees of latitude), so the results are not perfect (using 
plain long/lat coordinates), but they will probably be an adequate 
approximation.

BTW, for my application, I'm not interested in the distance per se, only 
in the points (e.g., boats) within a certain distance from the polygon 
(land). So I have also thought about a possible solution of using an 
expanded polygon, expanded in a certain number of kilometers outwards, 
and then using point-in-polygon (i.e., 'overlay') to find the points 
that are inside this new polygon. But I couldn't find a function to 
'grow' a polygon in this way.

-- 
Karl Ove Hufthammer