如何在R中处理ncdf栅格数据。

huangapple
go评论83阅读模式
英文:

How to handle a ncdf raster in R

问题

我正在使用一个类似于以下的栅格图层：

  1. class      : RasterLayer 
  2. dimensions : 7040, 9020, 63500800  (nrow, ncol, ncell)
  3. resolution : 1, 1  (x, y)
  4. extent     : 0.5, 9020.5, 0.5, 7040.5  (xmin, xmax, ymin, ymax)
  5. crs        : +proj=longlat +datum=WGS84 +no_defs 
  6. source     : omi_surface_no2_2005.nc 
  7. names      : surface_no2_ppb 
  8. zvar       : surface_no2_ppb

我需要重新投影它，以便能够裁剪到这个形状文件：

  1. Simple feature collection with 1 feature and 0 fields
  2. Geometry type: MULTIPOLYGON
  3. Dimension:     XY
  4. Bounding box:  xmin: -80.24869 ymin: 43.05051 xmax: -78.43696 ymax: 44.51657
  5. Geodetic CRS:  NAD83
  6.                     geometry
  7. 1 MULTIPOLYGON (((-79.38536 4...

但是当我尝试重新投影它时，它不起作用。

这是我使用的代码：

  1. omi_reproj <- projectRaster(omi, crs = crs(gtha_shp))

栅格图层是否被错误地分配了CRS？我不确定我做错了什么。如果你需要数据图层，我可以提供一个链接。

栅格链接: link

英文:

I'm working with a raster layer that looks like this:

  1. class      : RasterLayer 
  2. dimensions : 7040, 9020, 63500800  (nrow, ncol, ncell)
  3. resolution : 1, 1  (x, y)
  4. extent     : 0.5, 9020.5, 0.5, 7040.5  (xmin, xmax, ymin, ymax)
  5. crs        : +proj=longlat +datum=WGS84 +no_defs 
  6. source     : omi_surface_no2_2005.nc 
  7. names      : surface_no2_ppb 
  8. zvar       : surface_no2_ppb

And I need to re-project it so that I can crop it to this shape file:

  1. Simple feature collection with 1 feature and 0 fields
  2. Geometry type: MULTIPOLYGON
  3. Dimension:     XY
  4. Bounding box:  xmin: -80.24869 ymin: 43.05051 xmax: -78.43696 ymax: 44.51657
  5. Geodetic CRS:  NAD83
  6.                     geometry
  7. 1 MULTIPOLYGON (((-79.38536 4...

But when I try to re-project it, it doesn't work.

This is the code that I used:

  1. omi_reproj &lt;- projectRaster(omi, crs = crs(gtha_shp))

Has the raster layer been assigned the CRS incorrectly? I'm not sure what I'm doing wrong. If you need the data layers, I can provide a link.

Link to raster: link

答案1

得分: 0

这个文件不遵循存储栅格数据的CF规范。

  1. library(terra)
  2. #terra 1.7.11
  3. x <- rast("omi_surface_no2_2005.nc")
  4. #[1] "vobjtovarid4: **** WARNING **** I was asked to get a varid for dimension named dim1 BUT this dimension HAS NO DIMVAR! Code will probably fail at this point"
  5. #Warning messages:
  6. #1: In min(rs) : no non-missing arguments to min; returning Inf
  7. #2: In min(rs) : no non-missing arguments to min; returning Inf
  8. #3: In max(rs) : no non-missing arguments to max; returning -Inf
  9. #4: [rast] cells are not equally spaced; extent is not defined

你仍然可以使用ncdf4包读取值并手动创建一个SpatRaster。

打开ncdf文件并检查其内容。

  1. library(ncdf4)
  2. nc <- nc_open("omi_surface_no2_2005.nc")
  3. nc
  4. #    3 variables (excluding dimension variables):
  5. #        double surface_no2_ppb[lon_dim,lat_dim]   (Chunking: [752,587])  
  6. #        double LON_CENTER[dim1,latdim]   (Chunking: [1,9020])  
  7. #        double LAT_CENTER[londim,dim1]   (Chunking: [7040,1])

读取相关数据并关闭文件。

  1. lon <- ncdf4::ncvar_get(nc, nc$var[["LON_CENTER"]])
  2. lat <- ncdf4::ncvar_get(nc, nc$var[["LAT_CENTER"]])
  3. d <- ncdf4::ncvar_get(nc, nc$var[["surface_no2_ppb"]])
  4. nc_close(nc)

创建一个SpatRaster。

  1. library(terra)
  2. x <- rast(t(d[, ncol(d):1]), ext=c(range(lon), range(lat)), crs="+proj=lonlat")
  4. plot(sqrt(x))

如何在R中处理ncdf栅格数据。

英文:

This file does not follow the CF conventions for storing raster data.

  1. library(terra)
  2. #terra 1.7.11
  3. x &lt;- rast(&quot;omi_surface_no2_2005.nc&quot;)
  4. #[1] &quot;vobjtovarid4: **** WARNING **** I was asked to get a varid for dimension named dim1 BUT this dimension HAS NO DIMVAR! Code will probably fail at this point&quot;
  5. #Warning messages:
  6. #1: In min(rs) : no non-missing arguments to min; returning Inf
  7. #2: In min(rs) : no non-missing arguments to min; returning Inf
  8. #3: In max(rs) : no non-missing arguments to max; returning -Inf
  9. #4: [rast] cells are not equally spaced; extent is not defined

You can still read the values with the ncdf4 package and create a SpatRaster "by hand".

Open the ncdf file and inspect its contents

  1. library(ncdf4)
  2. nc &lt;- nc_open(&quot;omi_surface_no2_2005.nc&quot;)
  3. nc
  4. #    3 variables (excluding dimension variables):
  5. #        double surface_no2_ppb[lon_dim,lat_dim]   (Chunking: [752,587])  
  6. #        double LON_CENTER[dim1,latdim]   (Chunking: [1,9020])  
  7. #        double LAT_CENTER[londim,dim1]   (Chunking: [7040,1])

Read the relevant data and close the file

  1. lon &lt;- ncdf4::ncvar_get(nc, nc$var[[&quot;LON_CENTER&quot;]])
  2. lat &lt;- ncdf4::ncvar_get(nc, nc$var[[&quot;LAT_CENTER&quot;]])
  3. d &lt;- ncdf4::ncvar_get(nc, nc$var[[&quot;surface_no2_ppb&quot;]])
  4. nc_close(nc)

Create a SpatRaster

  1. library(terra)
  2. x &lt;- rast(t(d[, ncol(d):1]), ext=c(range(lon), range(lat)), crs=&quot;+proj=lonlat&quot;)
  4. plot(sqrt(x))

如何在R中处理ncdf栅格数据。

huangapple
  • 本文由 发表于 2023年2月18日 01:30:51
  • 转载请务必保留本文链接：https://go.coder-hub.com/75487483.html
  • projection
  • r
  • r-raster
  • raster
匿名

发表评论

匿名网友

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen:

确定