Find closest set of coordinates between two matrices

Question

I have two matrices as follows:

OBS = matrix(data=c(0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 
0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 
3, 4, 2, 4, 3, 5), 
nrow=6, ncol=3)
colnames(OBS)=c("Lat", "Lon", "Tas")

OBS = data.frame(OBS)

MOD = matrix(data=c(1.5, 3.0, 0.0, 0.0, 3, 4), nrow=2, ncol=3)
colnames(MOD)=c("Lat", "Lon", "Tas")

MOD = data.frame(MOD)

I want to use the coordinates in OBS and search for the closest set of coordinates from MOD and return the corresponding Tas values. The output should therefore be:

OUT = data.frame(c(3, 3, 3, 3, 4, 4))

I have applied the following solution:

library(geosphere)

# create distance matrix
mat <- distm(OBS[,c('Lon','Lat')], MOD[,c('Lon','Lat')], 
fun = distVincentyEllipsoid)

# Find shortest distance in matrix and assign tas values from MOD
OUT <- MOD$Tas[max.col(-mat)]

This works fine for this example, but if you try with datasets with several hundred or more rows then it no longer works. Anyone know why?

[This FAQ](https://stackoverflow.com/a/31668415/903061) is an excellent place to get started. — Gregor Thomas, Dec 17 '19 at 21:39
Many thanks for advising. I have now updated the question based on attempting one of the solutions from the FAQ. — DJ-AFC, Dec 19 '19 at 13:08

score 1 · Accepted Answer · answered Dec 19 '19 at 13:34

1

Maybe you can try the following code to see if it can work with larger dataset

OUT <- data.frame(x = MOD$Tas[apply(abs(outer(OBS$Lat+1i*OBS$Lon,MOD$Lat+1i*MOD$Lon,"-")),1,which.min)])

such that

answered Dec 19 '19 at 13:34

ThomasIsCoding

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Find closest set of coordinates between two matrices

1 Answers1