[R-sig-Geo] package spgwr: apply model parameters to a finer spatial scale

[Nikolaos Tziokas]

I using the *R* package *spgwr *to perform geographically weighted
regression (GWR). I want to apply the model parameters to a finer spatial
scale but I am receiving this error: *Error in validObject(.Object):
invalid class “SpatialPointsDataFrame” object: number of rows in data.frame
and SpatialPoints don't match*.

When I use another package for GWR, called *GWmodel*, I do not have this
issue. For example using the *GWmodel*, I do:

library(GWmodel)
library(sp)
library(raster)

ghs = raster("path/ghs.tif") # fine resolution raster
regpoints <- as(ghs, "SpatialPoints")

block.data = read.csv(file = "path/block.data.csv")

coordinates(block.data) <- c("x", "y")
proj4string(block.data) <- "EPSG:7767"

eq1 <- ntl ~ ghs
abw = bw.gwr(eq1,
             data = block.data,
             approach = "AIC",
             kernel = "gaussian",
             adaptive = TRUE,
             p = 2,
             parallel.method = "omp",
             parallel.arg = "omp")

ab_gwr = gwr.basic(eq1,
                   data = block.data,
                   regression.points = regpoints,
                   bw = abw,
                   kernel = "gaussian",
                   adaptive = TRUE,
                   p = 2,
                   F123.test = FALSE,
                   cv = FALSE,
                   parallel.method = "omp",
                   parallel.arg = "omp")

ab_gwr

sp <- ab_gwr$SDF
sf <- st_as_sf(sp)

# intercept
intercept = as.data.frame(sf$Intercept)
intercept = SpatialPointsDataFrame(data = intercept, coords = regpoints)
gridded(intercept) <- TRUE
intercept <- raster(intercept)
raster::crs(intercept) <- "EPSG:7767"

intercept = resample(intercept, ghs, method = "bilinear")

# slope
slope = as.data.frame(sf$ghs)
slope = SpatialPointsDataFrame(data = slope, coords = regpoints)
gridded(slope) <- TRUE
slope <- raster(slope)
raster::crs(slope) <- "EPSG:7767"

slope = resample(slope, ghs, method = "bilinear")

gwr_pred = intercept + slope * ghs

writeRaster(gwr_pred,
            "path/gwr_pred.tif",
            overwrite = TRUE)

How can I apply the GWR model parameters to a finer spatial scale, using
the spgwr package?

Here is the code, using the *spgwr *package:

library(spgwr)
library(sf)
library(raster)
library(parallel)

ghs = raster("path/ghs.tif") # fine resolution raster
regpoints <- as(ghs, "SpatialPoints")

block.data = read.csv(file = "path/block.data.csv")

#create mararate df for the x & y coords
x = as.data.frame(block.data$x)
y = as.data.frame(block.data$y)

#convert the data to spatialPointsdf and then to spatialPixelsdf
coordinates(block.data) = c("x", "y")

# specify a model equation
eq1 <- ntl ~ ghs

# find optimal ADAPTIVE kernel bandwidth using cross validation
abw <- gwr.sel(eq1,
               data = block.data,
               adapt = TRUE,
               gweight = gwr.Gauss)

# fit a gwr based on adaptive bandwidth
cl <- makeCluster(detectCores())
ab_gwr <- gwr(eq1,
              data = block.data,
              adapt = abw,
              gweight = gwr.Gauss,
              hatmatrix = TRUE,
              regpoints,
              predictions = TRUE,
              se.fit = TRUE,
              cl = cl)
stopCluster(cl)

#print the results of the model
ab_gwr

sp <- ab_gwr$SDF
sf <- st_as_sf(sp)

# intercept
intercept = as.data.frame(sf$Intercept)
intercept = SpatialPointsDataFrame(data = intercept, coords = regpoints)
gridded(intercept) <- TRUE
intercept <- raster(intercept)
raster::crs(intercept) <- "EPSG:7767"

intercept = resample(intercept, ghs, method = "bilinear")

# slope
slope = as.data.frame(sf$ghs)
slope = SpatialPointsDataFrame(data = slope, coords = regpoints)
gridded(slope) <- TRUE
slope <- raster(slope)
raster::crs(slope) <- "EPSG:7767"

slope = resample(slope, ghs, method = "bilinear")

gwr_pred = intercept + slope * ghs

writeRaster(gwr_pred,
            "path/gwr_pred.tif",
            overwrite = TRUE)

The fine resolution raster:
ghs = raster(ncols=47, nrows=92, xmn=582216.388, xmx=603366.388,
ymn=1005713.0202, ymx=1047113.0202, crs='+proj=lcc +lat_0=18.88015774
+lon_0=76.75 +lat_1=16.625 +lat_2=21.125 +x_0=1000000 +y_0=1000000
+datum=WGS84 +units=m +no_defs')

The csv can be downloaded from here
<https://drive.google.com/drive/folders/1V115zpdU2-5fXssI6iWv_F6aNu4E5qA7?usp=sharing>
.

-- 
Tziokas Nikolaos
Cartographer

Tel:(+44)07561120302
LinkedIn <http://linkedin.com/in/nikolaos-tziokas-896081130>

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