On Sun, Nov 22, 2009 at 6:23 PM, Michael Denslow <michael.dens...@gmail.com> wrote: > Dear r-sig-geo and Barry, > > I am getting a strange value when doing a query using the function > GNsrtm3 in the geonames package. > Here is the code. > > library(geonames) > GNsrtm3(34.63874,-79.10111) # outside Lumberton North Carolina USA! > > > srtm3 lng lat > 1 -32768 -79.10111 34.63874 > > Warning message: > In readLines(u) : > incomplete final line found on > 'http://ws.geonames.org/srtm3JSON?lat=34.63874&lng=-79.10111' > > > I think the elevation value should be around 47 meters. The geonames > website says 'ocean areas have been masked as "no data" and have been > assigned a value of -32768'. > http://www.geonames.org/export/web-services.html#srtm3 > I tried adjusting the lat, long values to query some nearby cells but > I still get -32768. > > Are these kinds of errors common in this dataset? Any suggestions? > I am would actually prefer to get an average elevation for the county > (Robeson) but am settling for the county centroid at this point.
I don't really know the details of the srtm3 data set, but I do see that geonames has two other DEM datasets - ASTER and GTOPO30. There's a function for GTOPO30 in geonames, but not ASTER. It's easy enough to write though: > GNaster=function(lat,lng){return(as.data.frame(geonames:::getJson("astergdemJSON",list(lat=lat,lng=lng))))} and I may include it in a new release (as well as getting rid of those end-of-line warnings). These two services agree with themselves and with you pretty well for your test location: > GNgtopo30(34.63874,-79.10111) gtopo30 lng lat 1 46 -79.10111 34.63874 > GNaster(34.63874,-79.10111) astergdem lng lat 1 47 -79.10111 34.63874 For an 'average' elevation you might be better off sampling many locations over your polygon. Barry _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo