getStations: A function to get a list of Personal Weather Station names

In steviep42/PWS: Final Project for STATS290

Description

This function looks on Wunderground to see if there are any PWS at a given lat/lon.

Usage

getStations(lldf, radius = 10, numofStatLimit = 150)

Arguments

lldf	A data frame of locations specified in lat/lon
radius	A distance / radius specified in miles
numofStatLimit	A cap on the number of stations

Details

This function is not meant to be called directly by users

Value

A list of PWS stations

Note

None

Author(s)

Steve Pittard <[e-mail]>

References

STATS290 Website

See Also

None

Examples

## The function is currently defined as
function (lldf, radius = 10, numofStatLimit = 150) 
{
    library(XML)
    library(RCurl)
    library(svMisc)
    dflength = length(lldf)
    if (dflength == 0) {
        stop("Hey. You passed an empty data frame. Unable to generate a list of stations !")
    }
    rlist = list()
    wunderString = "http://api.wunderground.com/auto/wui/geo/GeoLookupXML/index.xml?query="
    nrowdf = nrow(lldf)
    pStr = paste("Now checking Wunderground to find stations")
    print(pStr)
    for (ii in 1:nrowdf) {
        progress(ii, nrowdf - 1)
        lat = lldf[ii, c("geo_latitude")]
        lon = lldf[ii, c("geo_longitude")]
        coords = paste(lat, lon, sep = ",")
        urlstr = paste(wunderString, coords, sep = "")
        if (ii == (nrowdf - 1)) 
            cat("Done!\n")
        if (radius < 10) {
            halfradius = 3
        }
        else {
            halfradius = radius/6
        }
        qstring = paste("//location/nearby_weather_stations/pws/station[distance_mi<", 
            halfradius, "]/ancestor-or-self::station/id", sep = "")
        txt2parse = getURL(urlstr)
        hold = xmlTreeParse(txt2parse, useInternalNodes = TRUE)
        stationsXml = getNodeSet(hold, qstring)
        stations = sapply(stationsXml, xmlValue)
        rlist[[ii]] = stations
    }
    finalStationList = unique(unlist(rlist))
    if (length(finalStationList) == 0) {
        stop("No stations found")
    }
    else {
        if (length(finalStationList) > numofStatLimit) {
            length(finalStationList) = numofStatLimit
        }
        pStr = paste("Found", length(finalStationList), "Personal Weather Stations within", 
            radius, "miles", sep = " ")
        print(pStr)
        return(finalStationList)
    }
  }

steviep42/PWS documentation built on May 30, 2019, 5:39 p.m.