rainfall interpolation using ANN

Hi Nahm Lee and R-sig-geo,

I am quite interested in the IDW interpolation comparing to other methods
such as Krige, I have a code like this which I think also did the IDW:

library(gstat)
library(maptools)
library(raster)
dat71 <- readShapePoints("d:/FireDanger/IDW/71stations.shp")
bubble(dat71,"VALUE1")
sample.grid <- raster("rawsd_71Stations.tif")
Left <- bbox(sample.grid)[1]
Right <- bbox(sample.grid)[3]
Bottom <- bbox(sample.grid)[2]
Top <- bbox(sample.grid)[4]
cell.size <- res(sample.grid)
grid.xy <- expand.grid(x = seq(Left, Right, cell.size[1]), y = seq(Top,
Bottom, -cell.size[2]))
coordinates(grid.xy) <- ~x + y
gridded(grid.xy) = TRUE
value71.idw <- krige(VALUE1 ~ 1, dat71, grid.xy)
spplot(value71.idw["var1.pred"])
r_grid71 <- raster(value71.idw["var1.pred"])
plot(r_grid71)

However, I am not sure it is correct. Have someone using this method to do
the IDW? and One more question, How can I complete a Krige application
based on a shapefile (there are other examples using the spreedsheet).

Looking forward to hearing from you.

Peter

On Mon, Dec 1, 2014 at 12:31 PM, Nahm Lee <nlee at valleywater.org> wrote:

 This is my example with idw based on a web site, #
http://www.geo.ut.ee/aasa/LOOM02331/R_idw_interpolation.html.



Nahm Lee

nlee at valleywater.org







# http://www.geo.ut.ee/aasa/LOOM02331/R_idw_interpolation.html



library(ggplot2)

library(gstat)

library(sp)

library(maptools)

library(rgeos)



setwd("C:/Users/Michael/Dropbox/R/SHP")



AlertRain <- read.csv(file = "AlertRain.csv",header = TRUE)



names(AlertRain)



AlertRain_test <- AlertRain   # duplicate air temp. data file

AlertRain$x <- AlertRain$longitude  # define x & y as longitude and
latitude

AlertRain$y <- AlertRain$latitude



# Set spatial coordinates to create a Spatial object:

coordinates(AlertRain_test) = ~x + y



plot(AlertRain_test)



# Define the grid extent:

#x.range <- as.numeric(c(21.76, 28.21))  # min/max longitude of the
interpolation area

#y.range <- as.numeric(c(57.45, 59.72))  # min/max latitude of the
interpolation area



x.range <-
c(min(round(AlertRain_test$x,2)-0.1),max(round(AlertRain_test$x,2)+0.1))

y.range <-
c(min(round(AlertRain_test$y,2)-0.1),max(round(AlertRain_test$y,2)+0.1))



# Create a data frame from all combinations of the supplied vectors or
factors.

# See the description of the return value for precise details of the way
this is done.

# Set spatial coordinates to create a Spatial object. Assign gridded
structure:

grd <- expand.grid(x = seq(from = x.range[1], to = x.range[2], by = 0.1),
y = seq(from = y.range[1],

    to = y.range[2], by = 0.1))  # expand points to grid

coordinates(grd) <- ~x + y

gridded(grd) <- TRUE



#Plot the weather station locations and interpolation grid:

plot(grd, cex = 1.5, col = "grey")

points(AlertRain_test, pch = 1, col = "red", cex = 1)



# interpolate surface and fix the output:



idw <- idw(formula = Elevation ~ 1, locations = AlertRain_test,

    newdata = grd)  # apply idw model for the data

## [inverse distance weighted interpolation]



idw.output = as.data.frame(idw)  # output is defined as a data table

names(idw.output)[1:3] <- c("long", "lat", "var1.pred")  # give names to
the modelled variables



#Plot the results:



ggplot() + geom_tile(data = idw.output, aes(x = long, y = lat, fill =
var1.pred)) + scale_fill_gradient(low = "cyan", high = "orange")+

    geom_point(data = AlertRain, aes(x = longitude, y = latitude), shape
= 21,

        colour = "red")+labs(title = "Elevation by rainfall station
elevation")







*From:* R-sig-Geo [mailto:r-sig-geo-bounces at r-project.org] *On Behalf Of
*Mengxi Yang
*Sent:* Monday, December 01, 2014 1:32 AM
*To:* r-sig-geo at r-project.org
*Subject:* [R-sig-Geo] rainfall interpolation using ANN



Dear list,

I am going to do daily rainfall interpolation using ANN. but I am not
familiar with it. Can somebody give some advise or example?



my data like:

 I have 325 stations in different location.each station have unique code
and coordinates. And I want to interpolate in 1km resolution. I have the
mask map of NL.

[image: Inline image 2]



can someone give me some advice? because I want to compare ANN with
Kriging and IDW.

Thank you very much.



Mengxi Yang