Re: [R-sig-Geo] shortestPath in a loop

[Eric Carr]

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  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/
> questions/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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Re: [R-sig-Geo] Proj4string for NASA GPW v3 and Blue Marble world city light map?

[Eric Carr]

They also have this page:
http://sedac.ciesin.columbia.edu/data/set/gpw-v3-population-density/metadata

On Thu, May 7, 2015 at 11:11 AM, Shaun Walbridge swalbri...@esri.com
wrote:

 The specific projection information is contained within the raster
 datasets you download, in the related ASCII, Bil or GRID file. The
 metadata you see on that page is just a human readable representation of
 the data coverage, not intended to directly map to the full spatial
 reference.

 --
 Shaun Walbridge
 GIS Developer




 On 5/7/15, 5:15 AM, Ziyu Ma paul.ziyu...@gmail.com wrote:

 Dear all,
 
 I was working with a project concerning human population, using data from
 the Population Density Grid, version 3.
 
 I have hard time understanding the spatial reference from this metadata
 page:
 
 
 http://sedac.ciesin.columbia.edu/data/set/gpw-v3-population-density/metada
 ta
 
 Can I translate this into a proj4string so that I can use it as a CRS in
 R?
 
 Also, just out of curiosity, what it the spatial reference for NASA's Blue
 Marble maps, like the famous world city light map? Can I also use a
 proj4string to describe it?
 
 Thank you very much.
 
 Cheers,
 Ma
 
 Ziyu Ma
 PhD Student
 Ecoinformatics  Biodiversity,
 Department of Bioscience, Aarhus University
 Ny Munkegade 114, DK-8000 Aarhus C, Denmark
 
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Re: [R-sig-Geo] generating large, non-repeating, color palates for world maps

[Eric Carr]

200 colors seems extreme but    Cubehelix will generate a ramp of that
size.
http://www.mrao.cam.ac.uk/~dag/CUBEHELIX/cubetry.html
Eric

-Original Message-
From: r-sig-geo-boun...@r-project.org
[mailto:r-sig-geo-boun...@r-project.org] On Behalf Of Damian Maddalena
Sent: Wednesday, August 21, 2013 4:57 PM
To: r-sig-geo@r-project.org
Subject: [R-sig-Geo] generating large, non-repeating, color palates for
world maps

I am mapping regions generated using k-means clustering of ecological
variables at a global scale. I need to generate large random color ramps
(200 and 500 colors, for example) that do not repeat and implement them in
such a way as to minimize adjacency of similar colors. I am generating my
plots using spplot.

Currently, I generate my color ramps using rainbow() with the number of
categories in the spplot call as follows:

#df is a sp object of all land surface at .5 degree resolution. I am mapping
df$clusternum, a category that ranges from 1-n, where n is the number of
clusters.

n-200
spplot(df,zcol=clusternum,col.regions=rainbow(n,start=1/6,end=1),at=0:n)

Is there a better way to do this where I can a.) randomize the colors and
b.) minimize adjacency of similar colors?

Thank you.

-Damian

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