[R-sig-Geo] distmap

[Roger Bivand]

On Mon, 25 Jun 2007, Agustin Lobo wrote:

> I've tried (among other things):
>>  limit1 <- read.shape("limit_PNSN2000.shp")
> Shapefile type: Polygon, (5), # of Shapes: 2
>>  limit1poly <- Map2poly(limit1)
>>  limit1owin <- as(limit1poly,"owin")
> Error in .classEnv(thisClass) : unable to find an environment containing 
> class "polylist"
>
>>  limit2 <- readOGR("limit_PNSN2000.shp",layer="limit_PNSN2000")
> OGR data source with driver: ESRI Shapefile
> Source: "limit_PNSN2000.shp", layer: "limit_PNSN2000"
> with  2  rows and  1  columns

Then just:

limit1owin <- as(limit2,"owin")

ought to work with current maptools, or possibly coerce:

limit1owin <- as(as(limit2, "SpatialPolygons"), "owin")



>>  limit2poly <- Map2poly(limit1)
>>  limit1owin <- as(limit2poly,"owin")
> Error in .classEnv(thisClass) : unable to find an environment containing 
> class "polylist"
>>  limit1owin <- as(limit2,"owin")
> Error in as.owin.SpatialPolygons(from) : W must be a SpatialPolygons object
>
> I guess all I need is to convert my shapefile (read into R via read.shape or 
> readOGR?) into an object like letterR:
>
>>  data(letterR)
>>  str(letterR)
> List of 4
>  $ type  : chr "polygonal"
>  $ xrange: num [1:2] 2.02 3.93
>  $ yrange: num [1:2] 0.645 3.278
>  $ bdry  :List of 2
>   ..$ :List of 2
>   .. ..$ x: num [1:24] 2.03 2.02 2.02 2.66 2.66 ...
>   .. ..$ y: num [1:24] 3.278 3.248 0.653 0.653 1.695 ...
>   ..$ :List of 2
>   .. ..$ x: num [1:10] 2.65 2.64 3.04 3.12 3.16 ...
>   .. ..$ y: num [1:10] 2.23 2.70 2.71 2.63 2.50 ...
>  - attr(*, "class")= chr "owin"
>
> but how can I do it?
>
> Also, I'm so confused with so many spatial objects, is there a guide?

Please ignore all the non sp classes, that makes things simpler. The guide 
was in R News in 2005, and is still largely relevant for the Spatial* 
classes.

Roger

>
> Agus
>
> Roger Bivand escribió:
>>  On Fri, 22 Jun 2007, Agustin Lobo wrote:
>> 
>> >  Dear sig-geos,
>> > 
>> >  I have to calculate a distmap (that is, a map
>> >  in which the value of each cell is the distance
>> >  from the cell to a given object) for a set of polygons.
>> >  It seems to me that distmap.owin in spatstat would do it
>> >  fine, but distmap.owin does not accept objects
>> >  imported from shp vectors via readOGR. distmap.owin requires
>> >  type "polygonal" and readOGR yields class 'SpatialPolygonsDataFrame'
>> >  Is there any way to cast or convert from 'SpatialPolygonsDataFrame'
>> >  to "polygonal" or an alternative function to calculate the distances
>> >  to the boundaries of the polygons?
>>
>>  Have you tried coercing with as(x, "owin") in maptools?
>>
>>  Roger
>> 
>> > 
>> >  Thanks
>> > 
>> >  Agus
>> > 
>> >
>> 
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no