R：覆盖栅格图层的xy坐标

2023年7月31日 225次阅读

我有一个带有XY像素坐标的光栅,我希望将其转换为lat和long.

class       : RasterLayer 
dimensions  : 1617, 1596, 2580732  (nrow, ncol, ncell)
resolution  : 1, 1  (x, y)
extent      : 0, 1596, 0, 1617  (xmin, xmax, ymin, ymax)
coord. ref. : NA 
data source : C:\janW1.png 
names       : janW1 
values      : 0, 255  (min, max)

我使用here指定的公式计算了纬度/长度坐标.

这导致了以下数据帧

heads(cords)
       lat       lon   x      y janW1
1 46.99401 -14.99122 0.5 1616.5     0
2 46.99401 -14.97367 1.5 1616.5     0
3 46.99401 -14.95611 2.5 1616.5     0
4 46.99401 -14.93856 3.5 1616.5     0
5 46.99401 -14.92100 4.5 1616.5     0
6 46.99401 -14.90345 5.5 1616.5     0

如何覆盖或创建具有lat / long空间范围而不是图像坐标(XY像素)的重复栅格？或者是否有更简单的方法将像素转换为lat / Lon？

码

library(raster)
test <- raster('janW1.png')
data_matrix <- rasterToPoints(test)

#  Calculate longitude.

lonfract = data_matrix[,"x"] / (1596 - 1)
lon = -15 + (lonfract * (13 - -15))

#  Calculate latitude.

latfract = 1.0 - (data_matrix[,"y"] / (1617 - 1))  
Ymin = log(tan ((pi/180.0) * (45.0 + (47 / 2.0))))
Ymax = log(tan ((pi/180.0) * (45.0 + (62.999108 / 2.0))))
Yint = Ymin + (latfract * (Ymax - Ymin))
lat = 2.0 * ((180.0/pi) * (atan (exp (Yint))) - 45.0)

# Make single dataframe with XY pixels and latlon coords.
latlon <- data.frame(lat,lon)
tmp <- data.frame(data_matrix)
cords <- cbind(latlon, tmp)

janW1.png

最佳答案 更改栅格数据的投影并不像点(和线,多边形)那么简单.这是因为如果从当前单元格计算新坐标,它们将不在常规栅格中.

您可以使用函数projectRaster(raster package)来处理此问题.

library(raster)
test <- raster('janW1.png')

# In this case, you need to provide the correct crs to your data
# I am guessing. (this would be necessary for spatial data sets)
crs(test) <- '+proj=merc +datum=WGS84'

# you may also need to set the extent to actual coordinate values
# extent(test) <- c( , , ,) 
x <- projectRaster(test, crs='+proj=longlat +datum=WGS84')

或者,您可以将计算的值插入到新栅格中.有关示例,请参阅？raster :: interpolate.

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