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Re: Follow-up Q Crimestat/Splancs AI-GEOSTATS: point pattern analysis/ R question

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  • Carolyn & Richard Block
    Juliann I am not certain that Ned Levine, the developer of CrimeStat, has read this. I will forward it to him. Normal edge corrections don t work very well
    Message 1 of 4 , Sep 1, 2003
      Juliann
      I am not certain that Ned Levine, the developer of CrimeStat, has read this.
      I will forward it to him. Normal edge corrections don't work very well
      in looking at point patterns of crime because incidents of crime tend to
      cluster at city boundaries and jurisdictional changes. The program may be
      less tested for edge corrections than other things; however, CrimeStat 3 is
      now under development. Notification of any corrections and problems would
      be welcome.
      Dick
      ----- Original Message -----
      From: "Juliann Aukema" <aukemaj@...>
      To: <ai-geostats@...>; "fs" <jaukema@...>
      Sent: Friday, August 29, 2003 3:37 PM
      Subject: Follow-up Q Crimestat/Splancs AI-GEOSTATS: point pattern analysis/
      R question


      > I sent this a week or so ago and am resending because
      > I haven't seen it show up. Apologies if it did show up
      > for some of you.
      >
      > Hi thanks for the responses,
      >
      > Several people suggested using CrimeStat and one
      > person sent an R script for Splancs (below). I've
      > tried both of these with my data, trying to start as
      > simply as possible, and I do get nice looking output
      > when I put in the coordinates of all of my points
      > (haven't made it to subsets yet). However, when I use
      > CrimeStat with rectangular edge correction, my points
      > appear to be dispersed -below the envelope for larger
      > distances-(randomly distributed if I use no
      > correction) and when I use the Splancs script, they
      > appear to be aggregated -above the envelope for all
      > distances. I used 100 simulation replicates for both
      > methods. Any ideas why I would get such opposite
      > results? Would it be the edge correction, differences
      > in how L(d) is calculated, misinterpretation . . .? I
      > must be missing something.
      >
      > Thanks a lot,
      >
      >
      > Juliann
      >
      > > library(splancs)
      > >
      > > file<-"Filename.csv"
      > >
      > > point<-read.csv(file, header=TRUE, sep=";")
      > >
      > > box<-array(c(0,1000,1000,0,0,0,1000,1000),
      > > dim=c(4,2))
      > > s<-seq(0,500,5)
      > > rep<-100
      > >
      > > pointk<-khat(as.points(point), box,s, newstyle=TRUE)
      > > UL.khat<-Kenv.csr(length(point$x), box,rep, s)
      > >
      > > plot(s, sqrt(pointk$khat/pi)-s, type="l",
      > >
      >
      ylim=c(min(c(min(sqrt(pointk$khat/pi)-s),min(sqrt(UL.khat$lower/pi)-s)))-0.5
      > >
      > >
      > ,max(c(max(sqrt(pointk$khat/pi)-s),max(sqrt(UL.khat$upper/pi)-s)))+0.5),
      > >
      > > main=paste(sub(".csv","",file),"_RK", sep=""),
      > > xlab="Distance d (m)",
      > > ylab="L(d)-d")
      > > lines(s, sqrt(UL.khat$upper/pi)-s, lty=2)
      > > lines(s, sqrt(UL.khat$lower/pi)-s, lty=2)
      > > lines(s, s*0, lty=1)
      > >
      > > df<-data.frame(d=s, data=sqrt(pointk$khat/pi)-s,
      > > upper=sqrt(UL.khat$upper/pi)-s,
      > > lower=sqrt(UL.khat$lower/pi)-s)
      > >
      > > write.table(df,
      > > paste(sub(".csv","",file),"_RK",rep,".csv", sep=""),
      > >
      > > sep=";", row.names=TRUE)
      > >
      > > write.table(sqrt(pointk$khats/pi),
      > > paste(sub(".csv","",file),"_RKMap.csv",
      > > sep=""), sep=";", row.names=TRUE)
      > >
      > > dev.copy2eps()
      > >
      > > shell(paste("move rplot.eps
      > > ",sub(".csv","",file),"_RK",rep,".eps", sep=""))
      >
      >
      > ----------Original Post---------------------------
      > > At 14:05 19.08.2003 -0700, you wrote:
      > > > Good afternoon. I realize this is slightly
      > > >off-topic, but I thought it likely that someone on
      > > >this list could help and we could take further
      > > >discussion off-list.
      > > > I have a mapped set of about 800 points in a
      > > >Roughly rectangular plot and I would like to ask
      > > what
      > > >is the distribution of these points (random,
      > > regular,
      > > >aggregated, if aggregated- at what scale). I would
      > > >then like to ask the same question about various
      > > >subsets of points with respect to the underlying
      > > >distribution of points. (For example, suppose all
      > > the
      > > >points have an aggregated distribution, is a subset
      > > of
      > > >points aggregated more/less than expected given the
      > > >underlying aggregation). I thought Ripley's K would
      > > be
      > > >the way to go, but have been having trouble getting
      > > it
      > > >to work. I've been trying to do it in R. I've made
      > > >some graphics in R, but I'm really a novice and I
      > > find
      > > >that the help (including the bit in the Venables
      > > and
      > > >Ripley S-Plus book) is not quite sufficient to get
      > > me
      > > >going with the spatial part (I've played with
      > > >libraries Spatial, Spatstat, Splancs, GeoR).
      > > > My questions are:
      > > >---Is Ripley's K the way to go? Any suggestions on
      > > >that? Would you recommend something else?
      > > >---Software (preferably inexpensive)
      > > recommendations?
      > > >---Would anyone be willing to share an R program
      > > that
      > > >I could modify for my data and/or a sample or
      > > partial
      > > >data set to make sure I have my data structured
      > > >correctly for a particular library/procedure? (I
      > > found
      > > >this was the best way to make progress in SAS, but
      > > I
      > > >don't know many R or S-Plus users).
      > > >
      > > >Thanks a lot.
      > > >Juliann
      > > >aukemaj@...
      > > >
      > > >
      > > >__________________________________
      > > >Do you Yahoo!?
      > > >Yahoo! SiteBuilder - Free, easy-to-use web site
      > > design software
      > > >http://sitebuilder.yahoo.com
      > > >
      > > >--
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      > > >* As a general service to the users, please
      > > remember to post a summary of
      > > >any useful responses to your questions.
      > >
      > === message truncated ===
      >
      >
      >
      >
      >
      >
      > __________________________________
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