Coercion between sp objects and spatstat im objects
Functions to convert between spatstats raster format im and sps SpatialGridDataFrame as well as one-way conversion from rasters rasterLayer to im. S4-style as() coercion can be used between im and SpatialGridDataFrame objects.
as.im.SpatialGridDataFrame(from) as.SpatialGridDataFrame.im(from) as.im.RasterLayer(from, factor.col.name = NULL)
from |
object to coerce from |
factor.col.name |
column name of |
A SpatialGridDataFrame object may contain several columns of
data such that several values are associated with each grid cell. In contrast an
im object can only contain a single variable value for each cell. In
as.im.SpatialGridDataFrame() the first data column is used. To convert
another column to im format simply extract this column first as shown in
the example below.
signature(from = "SpatialGridDataFrame", to = "im")
signature(from = "im", to = "SpatialGridDataFrame")
In spatstat all spatial objects are assumed to be planar. This means
that spatstat is not designed to work directly with geographic
(longitude and latitude) coordinates. If a sp object is declared to
have geographic (unprojected) coordinates maptools refuses to convert
directly to spatstat format. Rather, these should be projected first
using e.g. spTransform. If you know what you are doing, and
really want to force coercion, you can overwrite the proj4string of the
sp object with NA, proj4string(x) <- CRS(NA), which
will fool the system to think that the data is in local planar coordinates.
This is probably not a good idea!
Edzer Pebesma edzer.pebesma@uni-muenster.de, Roger Bivand
Other converters between sp and spatstat:
as.ppp.SpatialPoints,
as.psp.SpatialLines,
as.owin.SpatialPolygons,
as.SpatialPolygons.tess.
run <- FALSE
if (require("spatstat.geom", quietly=TRUE)) run <- TRUE
if (run) {
## Extract an example SpatialGridDataFrame and plot it
data(meuse.grid) # A data.frame
gridded(meuse.grid) = ~x+y # Now a SpatialPixelsDataFrame
fullgrid(meuse.grid) <- TRUE # Finally a SpatialGridDataFrame
mg_dist <- meuse.grid["dist"] # A SpatialGridDataFrame with a single column
image(mg_dist, axes=TRUE)
}
if (run) {
## Convert to im format and plot it
mg_im <- as(mg_dist, "im")
plot(mg_im)
}
if (run) {
## Convert back to SpatialGridDataFrame and plot it again
mg2 <- as.SpatialGridDataFrame.im(mg_im)
image(mg2, axes=TRUE)
}
run <- run && require(raster, quietly=TRUE)
if (run) {
## Convert SpatialGridDataFrame -> RasterLayer -> im and plot it
r <- as(mg2, "RasterLayer")
r_im <- as.im.RasterLayer(r)
plot(r_im)
}
if (run) {
rr <- raster(nrow=2, ncol=3)
values(rr) <- 1:6
rr <- as.factor(rr)
rrr <- rr
f <- levels(rrr)[[1]]
f$name <- c("vector", "of", "values")
f$name2 <- letters[1:6]
levels(rrr) <- f
print(levels(rrr))
}
if (run) {
iii <- as.im.RasterLayer(rrr)
plot(iii)
}
if (run) {
iv <- as.im.RasterLayer(rrr, factor.col.name = "name")
plot(iv)
}
if (run) {
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