[R-sig-Geo] shortestPath in a loop

[marta azores]

Thanks for your quick reply to my question,

This ten points are ordered by time (date + time), and I know ,the points
are all connected.  I didn't include the column with the time in this
example, to make it simple.

After read your messages, I was looking the minimum spanning tree for the
vertices.
The advantage with the function "shortestPath" is that you have as result a
spatial line output, which I need it.
However, the minimum spanning tree give as output an ordiplot.

Is it possible to transform the ordiplot into spatialLines?

Thanks for your answers

Marta



2017-01-12 20:03 GMT-01:00 Eric Carr <carr at nimbios.org>:

> Generically independent of R, A graph and the connectivity between points
> needs defined before a shortest path algorithm can be applied.  If it
> assumes all points are connected, than the shortest path will be a straight
> line.  What you are looking for is some sort of  minimum spanning tree for
> the vertices.
> Eric
>
> On Thu, Jan 12, 2017 at 11:17 AM, marta azores <martazores at gmail.com>
> wrote:
>
>> Dear forum members,
>>
>> I would like to know how join several points with the aim to track a ship.
>>
>> After reading the documentation of some packages, I decided to use the
>> function shortestPath, but I only got the line between the first and the
>> last location of my points list. I need the complete survey, including also
>> the middle points. I try a loop to build the survey of the boats using
>> their locations, but It didn't work to me.
>>
>>
>> Any idea?
>>
>> Thanks in advance,
>>
>> Marta
>>
>> #script# it's also attached in a R.file: question loop2.R
>> ##########################################################
>> #
>> #raster# it's attached
>> azoTS1<- raster("C:/Users/Documents/azoTS1.tif")#wgs84
>> #
>> #10 points# it's attached
>> boat <- read.table("C:/Users/Documents/10pontos.csv", header=TRUE,
>> sep=",", na.strings="NA", dec=".", strip.white=TRUE)#
>> head(boat)
>>
>> #raster to transitionlayer
>> trCostS4<- transition(1/azoTS1, mean, directions=4)
>>
>> # points to spatialpointsdataframe
>> x=boat$Long1
>> y=boat$Lat1
>> coords = cbind(x, y)
>> plot(coords)
>> sp = SpatialPoints(coords, proj4string=CRS("+proj=longlat +ellps=WGS84
>> +datum=WGS84"), bbox = NULL)
>> sp
>> spdf=SpatialPointsDataFrame(sp,boat)
>> spdf
>> nrow(spdf)
>> plot(sp,axes=TRUE)
>> plot(spdf,add=TRUE, axes=TRUE)
>>
>> #shortestpath
>>
>> ## 1) this script only join the first point of the list and the last one,
>> and the points in the middle are not used.
>> CostpathSPdf <- shortestPath(trCostS4, spdf[1,], spdf[10,],
>> output="SpatialLines")
>> plot(CostpathSPdf,add=TRUE,axes=TRUE,col=2)#R_plot1.png (it's attached)
>>
>> ## 2) this script didn't work to me
>>
>> #first way from website: http://stackoverflow.com/quest
>> ions/8127066/loop-or-sapply-function-for-multiple-least-
>> cost-analysis-in-r?answertab=active#tab-top
>> for(i in 1:nrow(spdf)) {
>>   # Computation
>>   Costpath <- shortestPath(trCostS4, spdf[i,], spdf[10,],
>> output="SpatialLines")
>>   plot(Costpath)
>>
>> }
>>
>> #Error in validObject(.Object) :
>> #invalid class “SpatialLines” object: bbox should never contain infinite
>> values
>>
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>
>

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