terra::extract 精确 = TRUE 错误 TopologyException

Question

我正在比较 terra::extract 和exactextractr ::exact_extract 的功能。我注意到对于 terra::extract，

exact = TRUE

有时不起作用，但

weight=TRUE

可以。

1. 什么时候使用

   exact

   与

   weight

   比较好？

2. extract

   中的参数

   exact=TRUE

   是否存在错误？
3. 是否可以像

   exact_extract(rast, poly)

   中那样从多边形中获取像素重叠的比例，但是对于

   terra::extract

   ？

library(sf)
library(terra)
library(exactextractr)

rt=list(test1= matrix(1:100, ncol=10), 
     test2= matrix(201:300, ncol=10))

rast1 <- terra::rast((rt$test1))
rast2 <- terra::rast((rt$test1+2))

rast = c(rast1, rast2)

val1 = 0
val2 = 1.50
vac1= c(val1, val1, val2, val1, val2, val2, val1, val2, val1, val1)
vm1 = matrix(vac1, ncol = 2, byrow = TRUE)
pol1 = st_polygon(list(vm1))
pol2 = st_polygon(list(vm1+2))
pol3= st_polygon(list(vm1+4, vm1+6))
poly = st_sfc(pol1, pol2, pol3) %>% st_as_sf()

names(rast) <- c('t1', 't2')
rast_m=mask(rast, poly)

pt.pix = xyFromCell(rast, 1:100)


plot(rast_m[[1]]);plot(poly, add = TRUE)
plot(st_multipoint(pt.pix), add= TRUE, pch = ".", cex = 5)
text(st_multipoint(pt.pix+.15), labels = values(rast[[1]]))

values(rast_m[[1]]) %>% mean(., na.rm = T)

terra::extract(x = rast, y = poly, 'sum', exact = FALSE)


terra::extract(x = rast, y = poly, 'sum', exact = TRUE)

给出

Error: TopologyException: Input geom 1 is invalid: Hole lies outside shell at 6 6

但是有了

weight

，它就有效了...

terra::extract(x = rast, y = poly, 'mean', weight = TRUE)
# (10+10+4.5+19/4)/(1.5^2)
exact_extract(rast, poly, 'mean')
e = exact_extract(rast, poly)

Answer 1

那是因为

poly

几何图形无效：

sf::st_is_valid(poly)
# [1]  TRUE  TRUE FALSE

poly <- sf::st_make_valid(poly)
terra::extract(x = rast, y = poly, 'sum', exact = TRUE)
#   ID     t1     t2
# 1  1  29.25  33.75
# 2  2  69.75  74.25
# 3  3 261.00 270.00