Hi Chris, I don't have the packages you are using, but tracing this indicates that the page source contains the relative path of the graphic, in this case:
/nwisweb/data/img/USGS.12144500.19581112.20140309..0.peak.pres.gif and you already have the server URL: nwis.waterdata.usgs.gov getting the path out of the page source isn't difficult, just split the text at double quotes and get the token following "img src=". If I understand the arguments of "download.file" correctly, the path is the graphic.fn argument and the server URL is the graphic.url argument. I would paste them together and display the result to make sure that it matches the image you want. When I did this, the correct image appeared in my browser. I'm using Google Chrome, so I don't have to prepend the http:// Jim On Fri, Jun 5, 2015 at 2:31 AM, Curtis DeGasperi <curtis.degasp...@gmail.com> wrote: > I'm working on a script that downloads data from the USGS NWIS server. > dataRetrieval makes it easy to quickly get the data in a neat tabular > format, but I was also interested in getting the tabular text files - > also fairly easy for me using download.file. > > However, I'm not skilled enough to work out how to download the nice > graphic files that can be produced dynamically from the USGS NWIS > server (for example: > http://nwis.waterdata.usgs.gov/nwis/peak?site_no=12144500&agency_cd=USGS&format=img) > > My question is how do I get the image from this web page and save it > to a local directory? scrapeR returns the information from the page > and I suspect this is a possible solution path, but I don't know what > the next step is. > > My code provided below works from a list I've created of USGS flow > gauging stations. > > Curtis > > ## Code to process USGS daily flow data for high and low flow analysis > ## Need to start with list of gauge ids to process > ## Can't figure out how to automate download of images > > require(dataRetrieval) > require(data.table) > require(scrapeR) > > df <- read.csv("usgs_stations.csv", header=TRUE) > > lstas <-length(df$siteno) #length of locator list > > print(paste('Processsing...',df$name[1],' ',df$siteno[1], sep = "")) > > datall <- readNWISpeak(df$siteno[1]) > > for (a in 2:lstas) { > # Print station being processed > print(paste('Processsing...',df$name[a],' ',df$siteno[a], sep = "")) > > dat<- readNWISpeak(df$siteno[a]) > > datall <- rbind(datall,dat) > > } > > write.csv(datall, file = "usgs_peaks.csv") > > # Retrieve ascii text files and graphics > > for (a in 1:lstas) { > > print(paste('Processsing...',df$name[1],' ',df$siteno[1], sep = "")) > > graphic.url <- > paste('http://nwis.waterdata.usgs.gov/nwis/peak?site_no=',df$siteno[a],'&agency_cd=USGS&format=img', > sep = "") > peakfq.url <- > paste('http://nwis.waterdata.usgs.gov/nwis/peak?site_no=',df$siteno[a],'&agency_cd=USGS&format=hn2', > sep = "") > tab.url <- > paste('http://nwis.waterdata.usgs.gov/nwis/peak?site_no=',df$siteno[a],'&agency_cd=USGS&format=rdb', > sep = "") > > graphic.fn <- paste('graphic_',df$siteno[a],'.gif', sep = "") > peakfq.fn <- paste('peakfq_',df$siteno[a],'.txt', sep = "") > tab.fn <- paste('tab_',df$siteno[a],'.txt', sep = "") > > download.file(graphic.url,graphic.fn,mode='wb') # This apparently > doesn't work - file is empty > download.file(peakfq.url,peakfq.fn) > download.file(tab.url,tab.fn) > } > > # scrapeR > pageSource<-scrape(url="http://nwis.waterdata.usgs.gov/nwis/peak?site_no=12144500&agency_cd=USGS&format=img",headers=TRUE, > parse=FALSE) > page<-scrape(object="pageSource") > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
