I would suggest asking this on R-sig-geo.
https://stat.ethz.ch/mailman/listinfo/r-sig-geo
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Jeff NewmillerThe . . Go Live...
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Sent from my phone. Please excuse my brevity.
Mike Bock mb...@environcorp.com wrote:
I am working with spatial data in ggmap, generally with great success.
I have a huge data set with the coordinates in NAD 83 UTM Zone 11
(meters). To map the data the coordinates were converted to Lat Long
in GIS prior to use in R and ggmap/ggplot. I am using hexagonal binning
to aggregate the data :
#create bins and calculate stats
hb-hexbin(DF$lon,DF$lat,xbins=80,IDs=TRUE)
hb.avg-hexTapply(hb,DF$Res,mean,na.rm=TRUE)
hb.mx-hexTapply(hb,DF$Res,max,na.rm=TRUE)
hb.p80-hexTapply(hb,DF$Res,quantile,prob=0.80,na.rm=TRUE)
#create df for ggplot
hx_dat - data.frame(hcell2xy(hb), count = hb@count,
xo = hb@xcm, yo = hb@ycm, Mean=hb.avg,Max=hb.mx,
p80=hb.p80)
#Base Map
#BBox is the bounding box
Base-get_map(BBox,source='google')
m_hx-ggmap(Base,legend = bottom,
base_layer=ggplot(aes(x=x,y=y),data=hx_dat))
#Map of means
a-0.55
hc-'grey60'
m_hx+geom_hex(aes(x = x, y = y, fill = Mean),
color = hc, ,alpha=a,stat = identity) +
scale_fill_gradientn(Mean,colours=rev(rainbow(4)),trans='sqrt')
...and so on for other stats
I can also run statistical analyses on hx_dat.
By creating hexbins based on lat/long it seems there will be distortion
due to the differences in length of a degree at different locations on
the earth's surface. What is the most efficient way to eliminate this
distortion? Should I run hexbin in NAD83 and convert the x/y
coordinates to Lat Long? Can I get ggmap to convert the baselayer to
NAD84 and just do everything in NAD(my preferred option)?
I have tried converting Lat Long to NAD84 and back but the coordinates
are coming up in the eastern Pacific and not in California, so I am
missing something and I am not sure that is the best way to solve the
problem anyway. Thanks in advance, any help is greatly appreciated
Mike
Michael J. Bock, PhD | Senior Manager
mb...@environcorp.com
This message contains information that may be
confidenti...{{dropped:8}}
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
