更改R上的矩阵/栅格坐标

Question

I'm a beginner and I have worked a lot on my problem, but I am still stuck...

I have a matrix containing values of world temperature. The size is 360*720. The values are from -180, -90 (Longitude, latitude) to 180, 90 with a resolution of 0.5.

> head(matrix)

NaN.     NaN..1 NaN..2 NaN..3 NaN..4, [...] NaN..718 NaN..719
[1,]      Na      Na      Na      Na           Na      Na
[2,]      Na      Na      Na      Na           Na      Na
[3,]      Na      Na      Na      Na           Na      Na
[4,]      Na      Na      Na      Na           Na      Na
[5,]      Na      Na      Na      Na           Na      Na
[6,]   -1.6634 -1.6634 -1.6634 -1.6634       -1.6634 -1.7469
...

This matrix "looks like" a raster. My problem is that I don't know how to tell R the matrix resolution.

If I then rasterise and plot with plot(raster(matrix)) , I get this : http://postimg.org/image/gdnblob07/ Yet, I need the axis to be -180;180 (x) and -90;90 (y)

Do you know how I could do?

Thanks a lot

Answer 1

Using the raster package is the right intuition but when you instantiate it with just the matrix it doesn't get the extents accurately. This will do it:

library(raster)
r <- raster(nrow=360,ncol=720,vals=matrix)
plot(r)

raster will initialize a raster object with (by default), world boundaries. You can optionally specify the coordinate reference system (eg, crs="+proj=longlat +datum=WGS84"), and the extents (ymx, ymn, xmx, xmn). cell size is implicit and calculated from the extents and rows/cols.