R terra/raster: 上传 netcdf 文件会改变分辨率

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英文:

R terra/raster: uploading a netcdf file alters resolution

问题

I have netcdf files (GPM IMERG precipitation) which are supposed to be at 0.1x0.1 resolution like in the red box at the bottom here:

Well the pixel size is not exactly 0.1 on the image, but at least its height and width are the same.

However when uploading the netcdf via terra:: or raster:: the resolution slightly changes:

  1. class       : SpatRaster 
  2. dimensions  : 185, 97, 1  (nrow, ncol, nlyr)
  3. resolution  : 0.09999998, 0.1000001  (x, y)
  4. extent      : 34.2, 43.9, 62.3, 80.80002  (xmin, xmax, ymin, ymax)
  5. coord. ref. : lon/lat WGS 84 
  6. source      : _(1).nc:precipitationCal 
  7. varname     : precipitationCal (Daily accumulated precipitation (combined microwave-IR) estimate) 
  8. name        : precipitationCal 
  9. unit        :               mm 
  10. time (days) : 2000-06-04

Any solution on how to transform the rasters in R back to their original resolution would be welcomed. Btw, does this has to do with rounding coordinates of the extent in R packages?

英文:

I have netcdf files (GPM IMERG precipitation) which are supposed to be at0.1x0.1 resolution like in the red box at the bottom here:

R terra/raster: 上传 netcdf 文件会改变分辨率

Well the pixel size is not exactly 0.1 on the image, but at least its height and width are the same.

However when uploading the netcdf via terra:: or raster:: the resolution slightly changes:

  1. class       : SpatRaster 
  2. dimensions  : 185, 97, 1  (nrow, ncol, nlyr)
  3. resolution  : 0.09999998, 0.1000001  (x, y)
  4. extent      : 34.2, 43.9, 62.3, 80.80002  (xmin, xmax, ymin, ymax)
  5. coord. ref. : lon/lat WGS 84 
  6. source      : _(1).nc:precipitationCal 
  7. varname     : precipitationCal (Daily accumulated precipitation (combined microwave-IR) estimate) 
  8. name        : precipitationCal 
  9. unit        :               mm 
  10. time (days) : 2000-06-04

Any solution on how to transform the rasters in R back to their original resolution would be welcomed. Btw, does this has to do with rounding coordinates of the extent in R packages?

答案1

得分: 1

以下是您提供的翻译：

你能指向那个文件吗？据我所见，网站上显示的范围或分辨率要么是错误的。根据这些数字，应该是：

  1. print((43.9000038 - 34.20000855) / 97, digits=10)
  2. #[1] 0.09999995103

也许网站上的分辨率是使用单元格的中心计算的，所以你会得到

  1. print((43.95 - 34.15) / 97, digits=10)
  2. #[1] 0.1010309582

没有文件很难确定。但我会把赌注押在网站上是错的。

通过您的文件，我还看到了这个

  1. f <- "__1_.nc"
  2. r <- rast(f)
  3. res(r)
  4. #[1] 0.09999998 0.10000007

但从写入文件的角度来看，这是正确的。提供的单元格的x和y坐标并不严格规则（但几乎如此）。例如，这是前三个和后三个y坐标：

  1. 62.3500022888184 62.4500083923340 62.5499992370605 ...  
  2. 80.5500030517578 80.6500091552734 80.7500152587891

光从文件本身来看，我无法确定这些小数是否是有意的还是粗心造成的，我认为是后者，在这种情况下，四舍五入范围似乎是合理的：

  1. ext(r) <- round(ext(r), 4)
  2. r
  3. #class       : SpatRaster 
  4. #dimensions  : 185, 97, 1  (nrow, ncol, nlyr)
  5. #resolution  : 0.1, 0.1  (x, y)
  6. #extent      : 34.2, 43.9, 62.3, 80.8  (xmin, xmax, ymin, ymax)
  7. #coord. ref. : lon/lat WGS 84 
  8. #source      : __1_.nc:precipitationCal 
  9. #varname     : precipitationCal (Daily accumulated precipitation #(combined microwave-IR) estimate) 
  10. #name        : precipitationCal 
  11. #unit        :               mm 
  12. #time (days) : 2000-06-04
英文:

Can you point to that file? From what I can see, either the extent or the resolution shown on the website is wrong. Based on these numbers, it should be:

  1. print((43.9000038 - 34.20000855) / 97, digits=10)
  2. #[1] 0.09999995103

Perhaps for the website the resolution was computed using the center of the cells, so that you get

  1. print((43.95 - 34.15) / 97, digits=10)
  2. #[1] 0.1010309582

It is hard to be sure without the file. But I would put my money on the website being wrong.

With your file I also see this

  1. f <- "__1_.nc"
  2. r <- rast(f)
  3. res(r)
  4. #[1] 0.09999998 0.10000007

But that is correct in the sense that that does reflect the x and y coordinates written to the file. The x and y coordinates for the cells that are provided are not strictly regular (but nearly so). For example, here are the first and last three y coordinates:

  1. 62.3500022888184 62.4500083923340 62.5499992370605 ...  
  2. 80.5500030517578 80.6500091552734 80.7500152587891

From the file alone I cannot say whether these small decimals are intentional or stem from sloppiness, I assume the latter and in that case it indeed seems reasonable to round the extent:

  1. ext(r) <- round(ext(r), 4)
  2. r
  3. #class       : SpatRaster 
  4. #dimensions  : 185, 97, 1  (nrow, ncol, nlyr)
  5. #resolution  : 0.1, 0.1  (x, y)
  6. #extent      : 34.2, 43.9, 62.3, 80.8  (xmin, xmax, ymin, ymax)
  7. #coord. ref. : lon/lat WGS 84 
  8. #source      : __1_.nc:precipitationCal 
  9. #varname     : precipitationCal (Daily accumulated precipitation #(combined microwave-IR) estimate) 
  10. #name        : precipitationCal 
  11. #unit        :               mm 
  12. #time (days) : 2000-06-04

答案2

得分: 0

以下是翻译好的部分：

似乎修正了范围边界后，分辨率得到了纠正。以下是上传文件后的文件范围：

  1. r<-rast("file")
  2. ext(r)
  4. SpatExtent : 34.2000038226446, 43.9000022808711, 62.3000022535739, 80.8000152940335 (xmin, xmax, ymin, ymax)

我已经将范围坐标的小数部分四舍五入，分辨率得到了纠正：

  1. ext(r)<-c(34.2, 43.9, 62.3, 80.8)
  3. r
  5. class       : SpatRaster 
  6. dimensions  : 185, 97, 1  (nrow, ncol, nlyr)
  7. resolution  : 0.1, 0.1  (x, y)
  8. extent      : 34.2, 43.9, 62.3, 80.8  (xmin, xmax, ymin, ymax)
  9. coord. ref. : lon/lat WGS 84 
  10. source      : _(1).nc:precipitationCal 
  11. varname     : precipitationCal (Daily accumulated precipitation (combined microwave-IR) estimate) 
  12. name        : precipitationCal 
  13. unit        :               mm 
  14. time (days) : 2000-06-04
英文:

It seems that amending the extent boundaries corrects the resolution. Here is an extent of the file after uploading:

  1. r&lt;-rast(&quot;file&quot;)
  2. ext(r)
  4. SpatExtent : 34.2000038226446, 43.9000022808711, 62.3000022535739, 80.8000152940335 (xmin, xmax, ymin, ymax)

Ive rounded the decimals of the extent coordinates and the resolution was coreccted:

  1. ext(r)&lt;-c(34.2, 43.9, 62.3, 80.8)
  3. r
  5. class       : SpatRaster 
  6. dimensions  : 185, 97, 1  (nrow, ncol, nlyr)
  7. resolution  : 0.1, 0.1  (x, y)
  8. extent      : 34.2, 43.9, 62.3, 80.8  (xmin, xmax, ymin, ymax)
  9. coord. ref. : lon/lat WGS 84 
  10. source      : _(1).nc:precipitationCal 
  11. varname     : precipitationCal (Daily accumulated precipitation (combined microwave-IR) estimate) 
  12. name        : precipitationCal 
  13. unit        :               mm 
  14. time (days) : 2000-06-04

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  • 本文由 发表于 2023年5月18日 00:24:00
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  • netcdf4
  • r
  • r-raster
  • terra
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