[R-sig-Geo] reading a gps from R

[Patrick Giraudoux]

On the thread and in case it may help somebody, find below this function 
that can read Garmin Etrex Summit from R (whatever the plateform - 
tested on Windows XP and Ubuntu 6.10 Edgy eft) if gpsbabel is installed.

Packaged in pgirbric at http://perso.orange.fr/giraudoux/SiteGiraudoux.html.

readGPS<-function(type="w",wcom=4){

    if (!(type=="w" | type=="t")) stop("type must be 'w' (waypoints) or 
't' (tracks)")

    if (Sys.info()["sysname"]!="Windows") {# OK sous linux Ubuntu 6.10
        gpsdata<-system(paste("gpsbabel -",type," -i garmin -f 
/dev/ttyUSB0 -o tabsep -F -",sep=""), intern=TRUE)
        if (any(grep("Can't init",gpsdata))) stop("Cannot read GPS: 
check connexion")
        }
    else {# OK sous Windows
        if (any(grep(wcom,0:9))){
            gpsdata <- system(paste("gpsbabel -",type," -i garmin -f 
com",wcom,": -o tabsep -F -",sep=""), intern=TRUE)
            if (any(grep("Can't init",gpsdata))) stop("Cannot read GPS: 
check connexion and com port number 'wcom'")
            }
        else stop("Windows com port number 'wcom' must be one of 0:9")
    }
    gpsdata<-read.table(textConnection(gpsdata), fill=TRUE)
   
   
    if (type=="w"){
        gpsdata<-gpsdata[,c(2,6,7,17)]
        names(gpsdata)<-c("ident","long","lat","altitude")
        
gpsdata$altitude<-as.numeric(substr(as.character(gpsdata$altitude),1,nchar(as.character(gpsdata$altitude))-1))
        attributes(gpsdata)$type<-"Waypoints"
    }
   
    if (type=="t"){
        gpsdata<-gpsdata[,c(3,4,14)]
        names(gpsdata)<-c("long","lat","altitude")
        ident<-1:length(gpsdata[,1])
        gpsdata<-data.frame(ident=ident,gpsdata)
        
gpsdata$altitude<-as.numeric(substr(as.character(gpsdata$altitude),1,nchar(as.character(gpsdata$altitude))-1))
        attributes(gpsdata)$type<-"Track"
    }
   
    attributes(gpsdata)$sysTime<-Sys.time()
    gpsdata
}