R根据两个数据帧的经纬度计算距离 [英] R calculate distance based on latitude-longitude from two data frames

问题描述

我正在尝试根据条件从另一个数据帧中的值替换一个数据帧中的值.

I am trying to substitute values in a data frame from values in another data frame based on a condition.

这两个数据都包含纬度，经度和高度，但其中之一较短.我想从较短的数据框(5103行)中选择任意点，在第二个数据框(188426行)上找到纬度和经度上最接近的值(通过计算距离)，然后将最长数据框上的高度值替换为矮个子的高度.

Both data contain latitude, longitude and height but one of them is shorter. I want to pick any point from the shorter data frame (5103 rows) , find the closest values on latitude and longitude (by calculating distance) on the second one (188426 rows) and then replace the height value on the longest data frame with the height on the shorter one.

在下面的代码中，第一个数据帧是topo.rams，第二个数据帧是topo.msg.最终目的是将topo.msg中的高度替换为topo.rams中的高度值

The first data frame is topo.rams in the below code and the second is topo.msg. The final purpose is to substitute height in topo.msg with height values in topo.rams

topo.rams:
longitud,latitud,tempc,u,v,w,relhum,speed,topo
-1.7107, 38.1464, 18.2412, -6.1744, -0.3708, 0.0000, 58.6447, 6.3584,460.5908
-1.7107, 38.1734, 18.5915, -5.7757, -0.3165, 0.0000, 61.8492, 5.9840,416.0403

topo.msg
height,longitud,latitud
448.0, 1.70, 38.14
402.0, 1.70, 38.18

和所需的输出(已修改topo.msg)

and the desired output (topo.msg modified)

height,longitud,latitud
460.5908, 1.70, 38.14
416.0403,  1.70, 38.18

和使用的代码

#lectura de datos
topo.msg=read.csv("MSG_DEM.txt",sep=",",header=FALSE)
colnames(topo.msg) <- c("topoMSG","longitud","latitud")

topo.rams=read.csv("topografia-rams.txt",sep=",",header=TRUE)

# número de estaciones a tratar
puntos.rams=dim(topo.rams)[1]
puntos.msg=dim(topo.msg)[1]

# Localización del punto de MSG más próximo a la estación.
# Se calcula la distancia a partir de las coordenadas lat-lon

topo.temp=data.frame()

for(i in 1:puntos.rams)
{
  for(j in 1:puntos.msg) 
  {
  dlon<-topo.rams$longitud[i]-topo.msg$longitud

  if ( dlon < 0.5 && dlat < 0.5) {

    dlat<-topo.rams$latitud[i]-topo.msg$latitud

    if ( dlat < 0.5) {
       n1<-n1+1
       distancia=sqrt(dlon*dlon+dlat*dlat)

      }
    }
  indexj=which.min(distancia)
  }

  topo.msg$topo[indexj] = topo.rams$topo[i]

}

该代码似乎可以运行，但是需要很长时间.我还尝试从

This code seems to run but it takes a very long time. I have also tried to create a distance matrix with geosphere package from the post in Geographic distance between 2 lists of lat/lon coordinates But R complaints about allocating a 3.6 Gb.

我该如何解决这个问题?我想优化循环或使用距离矩阵.当然，必须有一种更清洁，更有效的距离计算方法.

How can I adress this issue? I would like to optimize the loop or to use distance matrix. For sure there has to be a cleaner, more efficient way to calculate distances.

预先感谢

推荐答案

根据帕特里克(Patric)的评论，我从循环转换为矩阵/矢量计算.现在，代码正在运行，更简单，更高效.

From the comment by Patric I switched from loop to matrix/vector computation. Now the code is running, simpler and more efficient.

for(i in 1:puntos.rams) 
{
  dlon<-topo.rams$longitud[i]-topo.msg$longitud
  dlat<-topo.rams$latitud[i]-topo.msg$latitud
  distancia<-matrix(sqrt(dlon*dlon+dlat*dlat))
  indexj=which.min(distancia)
  topo.temp$topo[indexj] = topo.rams$topo[i]
}

可能有一种更优雅的方法来进行此计算.我将不胜感激任何输入.

There's probably a more elegant way to do this calculation. I would appreciate any input.

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