[R-sig-Geo] spatialgridataframes

[Lyndon Estes]

Hi Mary,

I am not sure that I totally understand how you want to mask, so my
answer will probably be confused here.

If I understand you correctly, the landcover dataset extends outside
of the country you are studying, so you just want to limit the
analysis to certain landcovers falling within that country.

It sounds to me as if you have already selected the landcovers you
want, so I would again coerce both the country and "mask" to rasters
(maybe Edzer or somebody else can correct me if this is problematic).
Since it sounds like the landcover is bigger than the country, I would
use mask's extent to define the raster for "country"

mask.r <- raster(mask)

Presumably you have a polygon for the country, so to me it's easiest to do this:

cnt.r <- rasterize(SpatialPolygons(country), mask.r)

Then to use both to make a mask, you could do something like this:

my.mask <- mask.r & cnt.r

That should give you a mask for the landcovers you want within your country.

Hope this works and is relevant.

Cheers, Lyndon





On Mon, Feb 21, 2011 at 12:07 PM, Mary Rise <risemary48 at yahoo.com> wrote:
> Hi Lyndon,
> You are right it works for my data because my data is integer as shown:
> Data attributes:
>     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.     NA's
>     1.00     4.00     5.00     5.31     6.00     9.00 20735.00
>
> Question 1 is answered i managed to remove the class 9 so my landcover map
> is now having 8 classes. but i can not collapse these 8 classes into one
> because i will loose the classes on the legend.
> What i want to do now is to create a mask  by using the new landcover which
> is now RasterLayer ( because of this script m3 <- raster(landcover, layer =
> "band1", m4 <- m3 * ((m3 < 9) / (m3 < 9)) and country. I am still a beginner
> in using R .
>
> Question
> how can i create a mask from 2 different datasets which are:
> SpatialPolygonsDataFrame(country) defining the extend of study + the
> wanted sections are  under the new landcover map which is a
> SpatialGridDataFrame = mask
>
> Is this possible in R?
>
> Aim of creating this mask is to clip the other 5 datasets like DEM which are
> spatialgriddataframes.
> Thanks
>
> Mary
> ________________________________
> From: Lyndon Estes <lestes at princeton.edu>
> To: Mary Rise <risemary48 at yahoo.com>
> Cc: r-sig-geo-owner at r-project.org; r-sig-geo at r-project.org
> Sent: Sun, February 20, 2011 5:44:54 PM
> Subject: Re: [R-sig-Geo] spatialgridataframes
>
> Hi Mary,
>
> This might help answer your questions. I used the meuse dataset and
> converted to raster formats, but I think the general approach should
> work for what you want to do.
>
> library(raster)
> library(gstat)
> data(meuse.grid)
> coordinates(meuse.grid) = ~x+y
> gridded(meuse.grid) = TRUE
> class(meuse.grid)
> m2 <- as(meuse.grid, "SpatialGridDataFrame")
> m3 <- raster(m2, layer = "soil")  # Convert soil classes to raster
>
>>
>> Question1.
>> How can i remove the ninth class in R because it does not have to be
>> included in
>> geostatical analysis.
>
> m4 <- m3 * ((m3 < 3) / (m3 < 3))  # Removes class 3 from soil,
> converts it to NA values (this could also
> # serve as a mask)
>
> # If you want to keep that part of the grid in the analysis, then you
> might want to collapse the one class
> # into another
> m5 <- (m3 == 3 | m3 == 2) * 2 + (m3 == 1)  # Class 2 now includes 2 and 3
>
>> Question 2
>> how can i use the map created in Q1 to clip the other 5  aboventioned maps
>> (eg
>> DEM etc) or how can i create a mask from the map in Q1.
>>
>
>
> # Create a mask for just the area of soil class 1
> sc1.mask <- (m3 == 1) / (m3 == 1)
>
> # You then multiply your other rasters by your mask to reduce rasters
> to the areas you want to analyze.
>
> Cheers, Lyndon
>
>



-- 
Lyndon Estes
Research Associate
Woodrow Wilson School
Princeton University
+1-609-258-2392 (o)
+1-609-258-6082 (f)
+1-202-431-0496 (m)
lestes at princeton.edu