[R] latitude longitude data

[Mikkel Grum]

Dear R-helpers,

I get GPS readings with bug counts (bugs meaning
insects in this case) made along rows in crop fields
and use these to make maps of bug distribution.  The
GPS readings are not quite accurate enough for my
purpose, so since I know what row each reading is made
in, I adjust the latitudinal coordinate using:

    grd<-lm(lat~lon+Row,data)
    data$lat<-predict(grd[,c("lon","Row")])

which adjusts the latitude pretty well when the rows
run East-West, but not at all when the rows run
North-South, and it doesn't adjust the longitude at
all.

Is there a better approach I could use to adjust both
longitude and latitude onto the nearest point in the
row, whatever the direction of the rows? In other
words, move the point onto the row in a direction that
is perpendicular to the row?

cheers,
Mikkel