On Jul 23, 2010, at 7:13 AM, Mafalda Viana wrote:
Dear R users,
I need to find the coordinates for the point (midpoint) located half
way between two pairs of coordinates (lon1,lat1 and lon2,lat2)
assuming a straight line between them. What would be the best way? I
tried to find an answer in the help archives but without success. I
would greatly appreciate any help.
df<- data.frame(lon1=c(-4.568,-4.3980), lat1=c(59.235,56.369),
lon2=c(-5.123,-4.698), lat2=c(60.258,59.197) )
Wouldn't that just be the arithmetic average of the values? Or to you
have some need for a more accurate calculation based on spherical
geometry? Or some thing that will handle some other coordinate
weirdness?
> df$midlong <- apply(df[,c(1,3)], 1, mean)
> df$midlat <- apply(df[,c(2,4)], 1, mean)
> df
lon1 lat1 lon2 lat2 midlong midlat
1 -4.568 59.235 -5.123 60.258 -4.8455 59.7465
2 -4.398 56.369 -4.698 59.197 -4.5480 57.7830
--
David Winsemius, MD
West Hartford, CT
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