[R-sig-Geo] Aggregation to

[Miluji Sb]

Dear Loic,

Thank you for your reply and the suggestions - didn't realize that the
factor needs to be an integer.

The original data was at 0.5 degree, I aggregated it to 1 degree to match
to another data.

The original 0.5 degree data is available as a shapefile, I read it in
using readOGR and the information is as follows:

class       : SpatialPolygonsDataFrame
features    : 75228
extent      : -180, 180, -59.48429, 83.62742  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84
+towgs84=0,0,0
variables   : 4
names       :   gID, ISO3,         px,        py
min values  :     1,  AFG, -100.07055, -10.00004
max values  : 75228,  ZWE,  179.93522,  83.55961

Then I convert it to raster for aggregation using:

###
pgeo <- spTransform(poly, CRS('+proj=longlat +datum=WGS84'))
ext <- floor(extent(pgeo))
rr <- raster(ext, res=0.5)
rr <- rasterize(pgeo, rr, field=1)

This is the information on the converted raster:

class       : RasterLayer
dimensions  : 288, 720, 207360  (nrow, ncol, ncell)
resolution  : 0.5, 0.5  (x, y)
extent      : -180, 180, -60, 84  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
data source : in memory
names       : layer
values      : 1, 1  (min, max)

Then I aggregate it to 2.5 degree using:

###
aggregate(rr,fact=5, fun=sum)

This seems to have aggregate it to the desired 2.5 degree:

df2_5
class       : RasterLayer
dimensions  : 58, 144, 8352  (nrow, ncol, ncell)
resolution  : 2.5, 2.5  (x, y)
extent      : -180, 180, -61, 84  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
data source : in memory
names       : layer
values      : 1, 25  (min, max)

My goal is to use this to extract data from a rasterbrick (time series), so
I convert the raster to a spatialpointsdataframe:

###
spts <- rasterToPoints(df2_5, spatial = TRUE)

Then use extract from the the following rasterbrick:

class       : RasterBrick
dimensions  : 72, 144, 10368, 2880  (nrow, ncol, ncell, nlayers)
resolution  : 2.5, 2.5  (x, y)
extent      : 0, 360, -90, 90  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
names       : X0, X1, X2, X3, X4, X5, X6, X7, X8, X9, X10, X11, X12, X13,
X14, ...
z-value     : 0, 2879 (min, max)
varname     : beta
level       : 1

But I get a lot of missing values.Is it due to different extent? How can I
change the extent of the RasterBrick to (-180 180 -90 90)?

I realize that I have probably provided a lot of redundant information. Any
help will be highly appreciated. Thank you.

Sincerely,

Milu

On Thu, Aug 31, 2017 at 9:57 PM, Loïc Dutrieux <loic.dutrieux at conabio.gob.mx
> wrote:

>
>
> On 31/08/17 14:22, Miluji Sb wrote:
>
>> I have a set of coordinates:
>>
>> temp <- dput(head(gcp,10))
>> structure(list(lon = c(-180, -180, -179, -179, -178, -178, -177,
>> -176, -176, -175), lat = c(67, 68, 67, 68, 67, 68, 67, 66, 67,
>> 66)), datalabel = "", time.stamp = "11 Aug 2017 16:10", .Names = c("lon",
>> "lat"), formats = c("%9.0g", "%9.0g"), types = c(255L, 255L), val.labels =
>> c("",
>> ""), var.labels = c("lon", "lat"), version = 12L, row.names = c("1",
>> "2", "3", "4", "5", "6", "7", "8", "9", "10"), class = "data.frame")
>>
>> These are at 1 degree, I would like to aggregate them to 2.5 degree to use
>> them to extract data from a netcdf file (which is at 2.5 degree). This is
>> what I have done:
>>
>> rasterDF <- rasterFromXYZ(gcp)
>> gcp2_5 <- aggregate(rasterDF,fact=2.5, fun=sum)
>>
>
> The aggregation factor in raster::aggregate has to be an integer (2, 3,
> etc). Perhaps raster::resample is what you're looking for then. When using
> 'bilinear', resample actually aggregates to the nearest multiple of the
> original raster's resolution (2 degrees in your case), and finishes with
> some interpolation.
>
> Cheers,
> Loïc
>
>
>> However, this seems to return aggregated coordinates at 2 degree.
>>
>> class       : RasterLayer
>> dimensions  : 67, 180, 12060  (nrow, ncol, ncell)
>> resolution  : 2, 2  (x, y)
>> extent      : -180.5, 179.5, -54.5, 79.5  (xmin, xmax, ymin, ymax)
>> coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
>>
>> What am I doing wrong? Is there another way? Thank you.
>>
>> Sincerely,
>>
>> Milu
>>
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>>
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