使用 SF 聚合栅格中的值

问题描述

使用 SF 在栅格中聚合值

我需要的是为每个栅格汇总一些指标的值。 假设我们有一些数据 - 坐标和值，我想创建一个热图。

首先，我使用简单的要素框架创建了一个网格和栅格。 现在我需要获取 df 中的每个坐标并检查它们是否在一个栅格中。然后为每个栅格计算任何其他聚合函数的平均值。

# Packages ----------------------------------------------------------------


library(raster)
library(tidyverse)
library(sf)
library(sp)


# Border Data and Grid ----------------------------------------------------

Regions <- getData("GADM",country= "CZE",level = 1)
Regions %>% 


Regions <-
  Regions %>% st_as_sf()

grid_spacing <- 0.25

polygony <- st_make_grid(Regions,square = T,cellsize = c(grid_spacing,grid_spacing)) %>%
  st_sf()

plot(polygony,col = 'white')
plot(st_geometry(CZ),add = T)

A = st_intersection(polygony,CZ)


# Artifial Values to be use -----------------------------------------------
df <- 
  tibble(long = runif(500,13.27857,14),lat = runif(500,49,50),price = rnbinom(500,size = 40,0.3))

df %>% 
  ggplot(aes(long,lat,color = values)) + 
  geom_point()

A <- 
  A %>% 
  # Here Val shall be calculated as a mean of observations within each rastel grid cell
  mutate(val = rnorm(n = 202))

# Since not every raster cell has observations inside some NAN will be present
A[5,'val']  = NaN
A[25,'val']  = NaN

A %>% 
  ggplot(aes(fill = val)) + 
  geom_sf()



# What I need -------------------------------------------------------------

# For each raster in A calculate the mean of price for coordinates within this raster grid.

在 sf 框架中，我基本上需要一些等效的 https://www.rdocumentation.org/packages/raster/versions/3.4-5/topics/rasterize。

但是，我想绘制看起来像在示例中我真的需要栅格具有给定网格的形状。

解决方法

要汇总网格中的点值并保留 sf，您可以执行以下操作：

library(dplyr)
library(sf)

# get data. using your example,we'll take spatial data from the raster package
Regions <- raster::getData("GADM",country= "CZE",level = 1)

# convert spdf to sf
Regions <- Regions %>% st_as_sf()

# create a grid sf object
grid_spacing <- 0.25

polygony <- st_make_grid(Regions,square = T,cellsize = c(grid_spacing,grid_spacing)) %>%
  st_sf() %>% 
  mutate(ID = row_number()) # add a unique ID to each grid cell

# clip grid to shape of country polygons
A <- st_intersect(polygony,Regions)

# create fake data with coordinates and prices
df <- tibble(long = runif(500,13.27857,14),lat = runif(500,49,50),price = rnbinom(500,size = 40,0.3))

# convert the df to sf point layer
points <- st_as_sf(df,coords = c("long","lat"),crs = st_crs(A))

# spatially join grid to points,so that each point is assigned the grid ID into which it falls
pointsID <- st_join(points,A)

# group and summarize point values by grid ID
pointsID <- pointsID %>% 
  as.data.frame() %>% 
  group_by(ID) %>% 
  summarize(avg_price = mean(price))

# join aggregated values back to your grid
A<- left_join(A,pointsID,by = "ID")

plot(A["avg_price"])

,

因为您无论如何都使用光栅包

library(raster)
cze <- getData("GADM",level = 1)
r <- raster(cze,res=0.25)
df <- data.frame(long = runif(500,0.3))

r <- rasterize(df[,c("long","lat")],r,df$price,mean,background=0)
p <- as(r,"SpatialPolygonsDataFrame")
p <- crop(p,cze)

library(sf)
s <- st_as_sf(p)
plot(p)