英文:
Using dismo::randompoints in a loop
问题
I have an SF object consisting of 81 polygons.
What I would like to do is generate 460 random points within each polygon.
compared to st_sample, dismo::randomPoints has a few features I like to make use of; such as not having any created points be in the same raster cell as pre-existing points.
I am trying to loop the randompoints function to write random points for each row in my object "hrstest" (see reproducible example at the end of the question, "hrstest" has only 3 polygons instead of 81).
I also have pre-existing points ("samplexy"), and defining these within the randomPoints function ensures the resulting generated points are in cells of the masking raster ("mask") that do not contain any pre-existing points.
So I try the following:
papoints <- list()
for(i in 1:nrow(hrstest)){
papoints[i] <- randomPoints(mask=roads, n= 460, p=samplexy ext= hrstest[i,])
}
where "mask=roads" is the masking raster, and "p=samplexy" are the points that take prevalence in the raster (a raster cell containing point(s) from "samplexy", will not have points generated within it). As I see it this should then loop over each row (polygon) from "hrstest", resulting in 460 random points per polygon.
But it returns
Error in .doCellFromXY(object@ncols, object@nrows, object@extent@xmin, :
Not compatible with requested type: [type=list; target=double].
I could not figure out what this means, so tried taking a step back, and remove the requirement to not generate points within raster cells containing a point from 'samplexy'.
This runs, but does not give the correct result. It returns a warning for each list that is output:
Warning messages:
1: In papoints[i] <- randomPoints(mask = roads, n = 460, ext = hrstest[i, :
number of items to replace is not a multiple of replacement length
The real output is a list for each polygon (good), but instead of containing 460 points, each contains just one value, which looks like a longitude value in the crs I'm using (16N UTM).
Creating "hrstest":
structure(list(id = c("10_17", "10_18", "103_19"), area = c(9330.16971002,
11839.809165, 19727.1596434), Shape_Leng = c(45088.8473474, 54527.1219449,
203178.756164), Shape_Area = c(92923453.7616, 117622362.856,
168371931.317), size = c(92.9234537616, 117.622362856, 168.371931317
), geometry = structure(list(structure(list(list(structure(c(385555.4573,
385555.4573, 385758.714, 385855.4573, 385855.4573, 385991.2446,
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<details>
<summary>英文:</summary>
I have an SF object consisting of 81 polygons.
What I would like to do, is generate 460 random points within each polygon.
compared to st_sample, dismo::randomPoints has a few features I like to make use of;
such as not having any created points be in the same raster cell as pre-existing points.
I am trying to loop the randompoints function to write random points for each row in my object "hrstest" (see reproducible example at the end of the question, "hrstest" has only 3 polygons instead of 81).
[![enter image description here][1]][1]
I also have pre-existing points ("samplexy"), and defining these within the randomPoints function ensures the resulting generated points are in cells of the masking raster ("mask") that do not contain any pre-existing points.
So I try the following:
papoints <- list()
for(i in 1:nrow(hrstest)){
papoints[i] <- randomPoints(mask=roads,n= 460, p=samplexy ext= hrstest[i,])
}
whereby "mask=roads" is the masking raster, and "p=samplexy" are the points that take prevalence in the raster (a raster cell containing point(s) from "samplexy", will not have points generated within it). As I see it this should then loop over each row (polygon) from "hrstest", resulting in 460 random points per polygon.
But it returns
Error in .doCellFromXY(object@ncols, object@nrows, object@extent@xmin, :
Not compatible with requested type: [type=list; target=double].
I could not figure out what this means, so tried taking a step back, and remove the requirement to not generate points within raster cells containing a point from 'samplexy'.
This runs, but does not give the correct result. It returns a warning for each list that is output:
Warning messages:
1: In papoints[i] <- randomPoints(mask = roads, n = 460, ext = hrstest[i, :
number of items to replace is not a multiple of replacement length
The real output is a list for each polygon (good), but instead of containing 460 points, each contains just one value, which looks like a longitude value in the crs I'm using (16N UTM).
Creating "hrstest"
structure(list(id = c("10_17", "10_18", "103_19"), area = c(9330.16971002,
11839.809165, 19727.1596434), Shape_Leng = c(45088.8473474, 54527.1219449,
203178.756164), Shape_Area = c(92923453.7616, 117622362.856,
168371931.317), size = c(92.9234537616, 117.622362856, 168.371931317
), geometry = structure(list(structure(list(list(structure(c(385555.4573,
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5115569.6196, 5115380.8881, 5115126.2997, 5114561.7933, 5114561.7933,
5114261.7933), dim = c(196L, 2L)), structure(c(297955.4573, 297955.4573,
298555.4573, 298555.4573, 298555.4573, 298255.8337, 297955.4573,
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303055.4573, 303355.4573, 303355.4573, 302155.4573, 5112761.7933,
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5112761.7933), dim = c(7L, 2L)), structure(c(301555.4573, 301555.4573,
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302155.4573, 301555.4573, 5111861.7933, 5111561.7933, 5111561.7933,
5111261.7933, 5111261.7933, 5110961.7933, 5110961.7933, 5111861.7933,
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304555.4573, 304555.4573, 304255.4573, 5111261.7933, 5110961.7933,
5110961.7933, 5111261.7933, 5111261.7933), dim = c(5L, 2L)),
structure(c(302755.4573, 302755.4573, 303055.4573, 303055.4573,
302755.4573, 5110961.7933, 5110661.7933, 5110661.7933, 5110961.7933,
5110961.7933), dim = c(5L, 2L)), structure(c(301255.4573,
301255.4573, 300655.4573, 300655.4573, 301255.4573, 5110661.7933,
5110961.7933, 5110961.7933, 5110661.7933, 5110661.7933), dim = c(5L,
2L)), structure(c(299755.4573, 299755.4573, 299455.4573,
299455.4573, 298855.4573, 298855.4573, 300355.4573, 300355.4573,
299755.4573, 5110661.7933, 5110961.7933, 5110961.7933, 5110661.7933,
5110661.7933, 5110361.7933, 5110361.7933, 5110661.7933, 5110661.7933
), dim = c(9L, 2L)), structure(c(300955.4573, 300955.4573,
301255.4573, 301255.4573, 300955.4573, 300955.4573, 300655.4573,
300655.4573, 300955.4573, 5110061.7933, 5109761.7933, 5109761.7933,
5110061.7933, 5110061.7933, 5110361.7933, 5110361.7933, 5110061.7933,
5110061.7933), dim = c(9L, 2L)), structure(c(296755.4573,
296755.4573, 296155.4573, 296155.4573, 296455.4573, 296455.4573,
296755.4573, 5110061.7933, 5110361.7933, 5110361.7933, 5109761.7933,
5109761.7933, 5110061.7933, 5110061.7933), dim = c(7L, 2L
)), structure(c(292255.4573, 292255.4573, 291955.4573, 291955.4573,
292255.4573, 5110361.7933, 5110661.7933, 5110661.7933, 5110361.7933,
5110361.7933), dim = c(5L, 2L)), structure(c(297655.4573,
297655.4573, 297355.4573, 297355.4573, 297655.4573, 5111261.7933,
5111561.7933, 5111561.7933, 5111261.7933, 5111261.7933), dim = c(5L,
2L)), structure(c(299155.4573, 299155.4573, 298255.4573,
298255.4573, 299155.4573, 5112461.7933, 5112761.7933, 5112761.7933,
5112461.7933, 5112461.7933), dim = c(5L, 2L)), structure(c(299755.4573,
299755.4573, 300055.4573, 300055.4573, 299755.4573, 5109461.7933,
5109161.7933, 5109161.7933, 5109461.7933, 5109461.7933), dim = c(5L,
2L)), structure(c(291955.4573, 291955.4573, 292555.4573,
292555.4573, 291955.4573, 5109161.7933, 5108861.7933, 5108861.7933,
5109161.7933, 5109161.7933), dim = c(5L, 2L)), structure(c(302455.4573,
302455.4573, 302755.4573, 302755.4573, 303355.4573, 303355.4573,
302755.4573, 302755.4573, 302455.4573, 5108561.7933, 5107661.7933,
5107661.7933, 5107961.7933, 5107961.7933, 5108261.7933, 5108261.7933,
5108561.7933, 5108561.7933), dim = c(9L, 2L)), structure(c(300355.4573,
300355.4573, 299755.4573, 299755.4573, 298855.4573, 298855.4573,
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300655.4573, 300655.4573, 300055.4573, 300055.4573, 300355.4573,
5107961.7933, 5108261.7933, 5108261.7933, 5107961.7933, 5107961.7933,
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5106761.7933, 5106761.7933, 5107661.7933, 5107661.7933, 5107961.7933,
5107961.7933), dim = c(21L, 2L)), structure(c(290155.4573,
290155.4573, 289555.4573, 289555.4573, 288955.4573, 288955.4573,
289255.4573, 289255.4573, 289555.4573, 289555.4573, 289855.4573,
289855.4573, 290155.4573, 5106761.7933, 5107061.7933, 5107061.7933,
5107361.7933, 5107361.7933, 5107061.7933, 5107061.7933, 5106761.7933,
5106761.7933, 5106461.7933, 5106461.7933, 5106761.7933, 5106761.7933
), dim = c(13L, 2L)), structure(c(300355.4573, 300355.4573,
300055.4573, 300055.4573, 299755.4573, 299755.4573, 298855.4573,
298855.4573, 298255.4573, 298255.4573, 297955.4573, 297955.4573,
298255.4573, 298255.4573, 298555.4573, 298555.4573, 298855.4573,
298855.4573, 299455.4573, 299455.4573, 299755.4573, 299755.4573,
298855.4573, 298855.4573, 299455.4573, 299455.4573, 300055.4573,
300055.4573, 299755.4573, 299755.4573, 300055.4573, 300055.4573,
300655.4573, 300655.4573, 300355.4573, 300355.4573, 300655.4573,
300655.4573, 300355.4573, 300355.4573, 299455.4573, 299455.4573,
298855.4573, 298855.4573, 298555.4573, 298555.4573, 298255.4573,
298255.4573, 299155.4573, 299155.4573, 300355.4573, 5105261.7933,
5104961.7933, 5104961.7933, 5104661.7933, 5104661.7933, 5104961.7933,
5104961.7933, 5105261.7933, 5105261.7933, 5104961.7933, 5104961.7933,
5104661.7933, 5104661.7933, 5104361.7933, 5104361.7933, 5104061.7933,
5104061.7933, 5104361.7933, 5104361.7933, 5104061.7933, 5104061.7933,
5103461.7933, 5103461.7933, 5103161.7933, 5103161.7933, 5102861.7933,
5102861.7933, 5103161.7933, 5103161.7933, 5103461.7933, 5103461.7933,
5104061.7933, 5104061.7933, 5105261.7933, 5105261.7933, 5105861.7933,
5105861.7933, 5106161.7933, 5106161.7933, 5105861.7933, 5105861.7933,
5106161.7933, 5106161.7933, 5106461.7933, 5106461.7933, 5105861.7933,
5105861.7933, 5105561.7933, 5105561.7933, 5105261.7933, 5105261.7933
), dim = c(51L, 2L)), structure(c(300955.4573, 300955.4573,
301255.4573, 301255.4573, 300955.4573, 5105261.7933, 5104961.7933,
5104961.7933, 5105261.7933, 5105261.7933), dim = c(5L, 2L
)), structure(c(304555.4573, 304555.4573, 305155.4573, 305155.4573,
304855.4573, 304855.4573, 304555.4573, 5104661.7933, 5103761.7933,
5103761.7933, 5104361.7933, 5104361.7933, 5104661.7933, 5104661.7933
), dim = c(7L, 2L)), structure(c(301255.4573, 301255.4573,
301555.4573, 301555.4573, 301255.4573, 5103761.7933, 5103161.7933,
5103161.7933, 5103761.7933, 5103761.7933), dim = c(5L, 2L
)), structure(c(297655.4573, 297655.4573, 297355.4573, 297355.4573,
297655.4573, 5104061.7933, 5104361.7933, 5104361.7933, 5104061.7933,
5104061.7933), dim = c(5L, 2L)), structure(c(290755.4573,
290755.4573, 291055.4573, 291055.4573, 290755.4573, 5107661.7933,
5107061.7933, 5107061.7933, 5107661.7933, 5107661.7933), dim = c(5L,
2L)), structure(c(290155.4573, 290155.4573, 289855.4573,
289855.4573, 290155.4573, 5107661.7933, 5107961.7933, 5107961.7933,
5107661.7933, 5107661.7933), dim = c(5L, 2L)), structure(c(291055.4573,
291355.4573, 291355.4573, 291055.4573, 291055.4573, 290755.4573,
290755.4573, 291055.4573, 291055.4573, 5108261.7933, 5108261.7933,
5108561.7933, 5108561.7933, 5108261.7933, 5108261.7933, 5107961.7933,
5107961.7933, 5108261.7933), dim = c(9L, 2L)), structure(c(290455.4573,
290155.4573, 290155.4573, 290455.4573, 290455.4573, 290755.4573,
290755.4573, 290455.4573, 290455.4573, 5104961.7933, 5104961.7933,
5104361.7933, 5104361.7933, 5104961.7933, 5104961.7933, 5105261.7933,
5105261.7933, 5104961.7933), dim = c(9L, 2L)), structure(c(290755.4573,
290755.4573, 291355.4573, 291355.4573, 291055.4573, 291055.4573,
290755.4573, 5104661.7933, 5104361.7933, 5104361.7933, 5104961.7933,
5104961.7933, 5104661.7933, 5104661.7933), dim = c(7L, 2L
)), structure(c(296455.4573, 296455.4573, 296155.4573, 296155.4573,
296455.4573, 296455.4573, 297655.4573, 297655.4573, 297055.4573,
297055.4573, 296455.4573, 5102561.7933, 5102261.7933, 5102261.7933,
5101961.7933, 5101961.7933, 5101361.7933, 5101361.7933, 5101961.7933,
5101961.7933, 5102561.7933, 5102561.7933), dim = c(11L, 2L
)), structure(c(301855.4573, 301855.4573, 302155.4573, 302155.4573,
302455.4573, 302455.4573, 302755.4573, 302755.4573, 301855.4573,
5101361.7933, 5100761.7933, 5100761.7933, 5100461.7933, 5100461.7933,
5100761.7933, 5100761.7933, 5101361.7933, 5101361.7933), dim = c(9L,
2L)), structure(c(304555.4573, 304555.4573, 304855.4573,
304855.4573, 304555.4573, 5100761.7933, 5100461.7933, 5100461.7933,
5100761.7933, 5100761.7933), dim = c(5L, 2L)), structure(c(300955.4573,
300955.4573, 300655.4573, 300655.4573, 300955.4573, 5099861.7933,
5100761.7933, 5100761.7933, 5099861.7933, 5099861.7933), dim = c(5L,
2L)), structure(c(300055.4573, 300055.4573, 299755.4573,
299755.4573, 300055.4573, 5100761.7933, 5101061.7933, 5101061.7933,
5100761.7933, 5100761.7933), dim = c(5L, 2L)))), class = c("XY",
"MULTIPOLYGON", "sfg"))), class = c("sfc_MULTIPOLYGON", "sfc"
), precision = 0, bbox = structure(c(xmin = 287709.0977, ymin = 5099416.5347,
xmax = 389035.5557, ymax = 5187921.0511), class = "bbox"), crs = structure(list(
input = "unknown", wkt = "PROJCRS["unknown",\n BASEGEOGCRS["GCS_unknown",\n DATUM["World Geodetic System 1984",\n ELLIPSOID["WGS 84",6378137,298.257223563,\n LENGTHUNIT["metre",1]],\n ID["EPSG",6326]],\n PRIMEM["Greenwich",0,\n ANGLEUNIT["Degree",0.0174532925199433]]],\n CONVERSION["UTM zone 16N",\n METHOD["Transverse Mercator",\n ID["EPSG",9807]],\n PARAMETER["Latitude of natural origin",0,\n ANGLEUNIT["Degree",0.0174532925199433],\n ID["EPSG",8801]],\n PARAMETER["Longitude of natural origin",-87,\n ANGLEUNIT["Degree",0.0174532925199433],\n ID["EPSG",8802]],\n PARAMETER["Scale factor at natural origin",0.9996,\n SCALEUNIT["unity",1],\n ID["EPSG",8805]],\n PARAMETER["False easting",500000,\n LENGTHUNIT["metre",1],\n ID["EPSG",8806]],\n PARAMETER["False northing",0,\n LENGTHUNIT["metre",1],\n ID["EPSG",8807]],\n ID["EPSG",16016]],\n CS[Cartesian,2],\n AXIS["(E)",east,\n ORDER[1],\n LENGTHUNIT["metre",1,\n ID["EPSG",9001]]],\n AXIS["(N)",north,\n ORDER[2],\n LENGTHUNIT["metre",1,\n ID["EPSG",9001]]]]"), class = "crs"), n_empty = 0L)), row.names = c(NA,
-3L), sf_column = "geometry", agr = structure(c(id = NA_integer_,
area = NA_integer_, Shape_Leng = NA_integer_, Shape_Area = NA_integer_,
size = NA_integer_), levels = c("constant", "aggregate", "identity"
), class = "factor"), class = c("sf", "tbl_df", "tbl", "data.frame"
))
Creating "samplexy"
structure(list(X = c(293859.5241, 297077.2033, 293824.4975, 302682.9115,
298934.3725, 302925.7667, 305010.6482, 292583.6686, 300802.0569,
293888.2412, 293998.3872, 297002.6123, 297002.5627, 300887.6253,
304739.1686), Y = c(5107678.897, 5103268.472, 5107719.002, 5100904.022,
5103984.938, 5112739.93, 5102591.506, 5105784.204, 5105996.207,
5109226.247, 5107712.057, 5109400.563, 5104080.651, 5105794.349,
5106965.357), geometry = structure(list(structure(c(293859.5241,
5107678.897), class = c("XY", "POINT", "sfg")), structure(c(297077.2033,
5103268.472), class = c("XY", "POINT", "sfg")), structure(c(293824.4975,
5107719.002), class = c("XY", "POINT", "sfg")), structure(c(302682.9115,
5100904.022), class = c("XY", "POINT", "sfg")), structure(c(298934.3725,
5103984.938), class = c("XY", "POINT", "sfg")), structure(c(302925.7667,
5112739.93), class = c("XY", "POINT", "sfg")), structure(c(305010.6482,
5102591.506), class = c("XY", "POINT", "sfg")), structure(c(292583.6686,
5105784.204), class = c("XY", "POINT", "sfg")), structure(c(300802.0569,
5105996.207), class = c("XY", "POINT", "sfg")), structure(c(293888.2412,
5109226.247), class = c("XY", "POINT", "sfg")), structure(c(293998.3872,
5107712.057), class = c("XY", "POINT", "sfg")), structure(c(297002.6123,
5109400.563), class = c("XY", "POINT", "sfg")), structure(c(297002.5627,
5104080.651), class = c("XY", "POINT", "sfg")), structure(c(300887.6253,
5105794.349), class = c("XY", "POINT", "sfg")), structure(c(304739.1686,
5106965.357), class = c("XY", "POINT", "sfg"))), class = c("sfc_POINT",
"sfc"), precision = 0, bbox = structure(c(xmin = 292583.6686,
ymin = 5100904.022, xmax = 305010.6482, ymax = 5112739.93), class = "bbox"), crs = structure(list(
input = NA_character_, wkt = NA_character_), class = "crs"), n_empty = 0L)), sf_column = "geometry", agr = structure(c(X = NA_integer_,
Y = NA_integer_), levels = c("constant", "aggregate", "identity"
), class = "factor"), row.names = c("1", "2", "3", "4", "5",
"6", "7", "8", "9", "10", "11", "12", "13", "14", "15"), class = c("sf",
"data.frame"))
[1]: https://i.stack.imgur.com/s2L40.png
</details>
# 答案1
**得分**: 1
1. 使用双括号分配一个列表项（[为什么][1]？）
2. 将您的类 'sf' 对象 "samplexy" 转换为 `randomPoints` 所需的类 'Spatial*'：
3. 使用类 'extent' 的对象设置范围：
```R
library(sf)
library(dismo)
library(raster)
for(i in 1:nrow(hrstest)){
papoints[[i]] <- ## (1)
dismo::randomPoints(mask = roads, n = 460,
p = as_Spatial(samplexy), ## (2)
ext = extent(st_bbox(hrstest[i,])) ## (3)
)
}
## > papoints[[1]] |> head()
## x y
## [1,] 313040.7 5183496
## [2,] 373836.6 5165795
## [3,] 292775.4 5130393
## [4,] 313040.7 5165795
## [5,] 353571.3 5103842
## [6,] 333306.0 5174645
英文:
It should work if you
- use the double bracket to assign a list item (why?)
- convert your class 'sf' object "samplexy" to class 'Spatial*' required by
randomPoints - set the extent with an object of class 'extent':
library(sf)
library(dismo)
library(raster)
for(i in 1:nrow(hrstest)){
papoints[[i]] <- ## (1)
dismo::randomPoints(mask = roads, n = 460,
p = as_Spatial(samplexy), ## (2)
ext = extent(st_bbox(hrstest[i,])) ## (3)
)
}
## > papoints[[1]] |> head()
## x y
## [1,] 313040.7 5183496
## [2,] 373836.6 5165795
## [3,] 292775.4 5130393
## [4,] 313040.7 5165795
## [5,] 353571.3 5103842
## [6,] 333306.0 5174645
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
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