On 02/06/17 01:17, lluis.hurt...@uv.es wrote:
Dear all,
I am currently working with the spatstat package, using windows and pixel
images.
First:
My aim is to transform a shapefile (see attached) into a pixel image.
My idea is to start transforming the shapefile into a Spatial Polygon file:
x <- readShapeSpatial("200001441.shp")
y <- as(x, "SpatialPolygons")
z <- as.owin(y)
Given z, I want to identify each polygon with a single constant value. This is
like adding marks to the SpatialPolygons file. Then I want to convert these
polygons into an image, such that the value of each pixel corresponds to the
value associated to the polygon where the pixel lies.
I have been able to do this individually, polygon by polygon, but then I cannot
merge the resulting images into a single one. Any idea?
Second:
I would also need a single window containing all the smallest polygons (the
boundary). I have tried:
w <- union.owin(z)
But the resulting window w still shows internal polygons. As read in spatstas
FAQ page:
"First, convert each of the regions into a separate owin object. Then apply
union.owin to combine them."
So I try,
regions <- slot(y, "polygons")
regions <- lapply(regions, function(x) { SpatialPolygons(list(x)) })
windows <- lapply(regions, as.owin)
But windows is a list of 4307 polygons. How can introduce all of them as a
single argument?
M <- union.owin(windows)
Warning messages:
1: In union.owin(windows) : Some arguments were not windows
2: In union.owin(windows) : No windows were given
Thank you very much for you help.
As Don has said, this question would be better asked on R-sig-geo.
A *reproducible* example would be nice, e.g. perhaps you could tell us
how to get the shapefile in question.
In respect of your last point: Rather than "M <- union.owin(windows)"
you should use:
M <- do.call(union.owin, windows)
But that's rather off the track. What I think you should do (it's hard
to be certain without a reproducible example) is something like:
tw <- tess(tiles=windows)
iw <- as.im(funxy(as.function(tw,values=vvv),W=Window(tw)),dimyx=128)
where "vvv" is a vector of the values that you wish to associate with
the individual polygons. There may be less cryptic ways of
accomplishing the same thing, but this is the sexiest way, I think.
The value chosen for "dimyx", i.e. 128, is just by way of example. You
can use whatever value suits you. The larger it is, the smoother the
individual polygons will look, in pixellated form, but the longer things
will take. With 4307 polygons, that might be a rather long time!
HTH
cheers,
Rolf Turner
--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276
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