用R中的级别绘制netcdf文件 [英] Plotting netcdf file with levels in R

问题描述

我最近开始在R中使用netcdf.示例数据在这里:

I have recently started to work with netcdf in R. Sample data is here:

http://www.earthstat.org/data-download/>已收获175种作物的作物面积和单产>单季作物>大豆_HarvAreaYield2000_NetCDF

http://www.earthstat.org/data-download/ > Harvested area and yield for 175 crops > individual crops > soybean_HarvAreaYield2000_NetCDF

在此文件夹中，有一个名为soybean_AreaYieldProduction.nc

In this folder, there is a netcdf file called soybean_AreaYieldProduction.nc

这是我打开netcdf的方式

This is how I open the netcdf

 library(ncdf4)

 dat <- nc_open("soybean_AreaYieldProduction.nc")
 print(soy)

1 variables (excluding dimension variables):
    float soybeanData[longitude,latitude,level,time]  
LayerDescriptions: struct(5).Data(:,:,1/2/3/4/5/6) to access data layer: 1=Harvested Area fraction, 2=Yield 3=Harvested Area data quality, 4=Yield data quality, 5=Harvested Area in hectares, 6= Production
        Units: Harvested Area Fraction(1)=percent of gridcell that was harvested, Yield(2)=metric tons per hectare, Harvested Area Hectares(5)=total hectares harvested per gridcell, Production(6)=Metric Tons
        DataQuality: In levels 3 and 4, a value of 1 = county; .75 = state; .5 = interpolated from within 2 degrees lat/long; .25 = country; 0 = missing.
4 dimensions:
        longitude  Size:4320
        units: longitude
        latitude  Size:2160
        units: latitude
        level  Size:6
        time  Size:1

我想绘制每个级别，但不知道如何为每个级别提取数据.

I want to plot each level but do not know how to extract data for each level.

这是我提取lon和lat数据的方式:

This is how I extract lon and lat data:

lon <- ncvar_get(dat,"longitude") # extract long

lat <- ncvar_get(dat,"latitude") # extract lat

但是我如何提取单个水平?

But how do I extract individual levels?

level.1 <- ncvar_get(dat, ????) 

最终目的是可视化每个级别 我想使用以下命令进行可视化:

Ultimate aim is to visualize each levels I want to visualize using the following command:

image(lon,lat, level)

推荐答案

使用raster包可能最简单:

library(raster)
r1 <- raster("soybean_AreaYieldProduction.nc", level=1)
r2 <- raster("soybean_AreaYieldProduction.nc", level=2)

plot(r1)
image(r1) 
s <- stack(r1, r2)
plot(s)

其他绘图方法

spplot(s)

library(rasterVis)
levelplot(r1) 
levelplot(s)

并在CRAN上查看其他映射包

And see other mapping packages on CRAN

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