[R-sig-Geo] R-sig-Geo Digest, Vol 26, Issue 12

[Denis Chabot]

Hi Roger,

Many thanks for Rgshhs. I am very glad to have this additional source  
of coastlines.

A few comments.

I am impressed with axis label handling when using the "plot" command  
on the spatial polygons imported by Rghhs. I like the suffix given to  
each number, e.g. "300°E". How do you do this? Setting some kind of  
"unit" attribute to the longitudes and latitudes? I don't know how to  
do this, otherwise I'd implement it in the maps I produce with  
PBSmapping.

Second surprise: I reimported the same area but using the option  
"shift=TRUE" to get longitudes West. I'm used to these numbers being  
negative, and indeed they still are here as I must select negative  
longitudes to define xlim. But when issuing the plot command, they  
are labelled properly, i.e. -70 becomes "70°W". In PBSmapping I must  
turn automatic xaxis labelling off and relabel myself. I may switch  
to your classes and methods yet!

However in my first test, I got the lakes to be coloured "azure2" but  
not the ocean, which was white:

NWA.i <- Rgshhs("gshhs_i.b", shift=TRUE, xlim = c(280,340), ylim = c 
(35,75), verbose = TRUE)
plot(NWA.i$SP, xlim=c(-70, -55), ylim=c(45, 51), col="khaki",  
pbg="lightblue", axes=T)

So I read the html doc on sp and discovered pbg was the color of  
"holes", which lakes are but not the ocean, which is just the absence  
of polygons. So I added a bg color to the above plot command, which  
should have taken care of that, but it did not. Do you know why?

Another question: the help on Rgshhs says we can import only land,  
for instance, instead of the 4 hierarchic types in gshhs files, by  
adding "level=1". But if I import everything, can I decide later to  
make a plot with land only? Or to create a layer with only lakes (no  
coastline)? I consulted the help for sp as well as the documentation  
for sp but could not figure out how to do this. When I print the list  
created by Rgshhs or even just the SP part of it, I see that SP is  
made of "slots", one of which contains the level. This information is  
also available in the spatialdata part. But I don't know how to  
select just the polygons with "level==2".

Cheers,

Denis
Le 05-10-22 à 06:00, r-sig-geo-request at stat.math.ethz.ch a écrit :

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> Today's Topics:
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>    1. New sp add-on packages on sourceforge repository (Roger Bivand)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 21 Oct 2005 15:10:43 +0200 (CEST)
> From: Roger Bivand <Roger.Bivand at nhh.no>
> Subject: [R-sig-Geo] New sp add-on packages on sourceforge repository
> To: r-sig-geo at stat.math.ethz.ch
> Message-ID: <Pine.LNX.4.44.0510211454280.19619-100000 at reclus.nhh.no>
> Content-Type: TEXT/PLAIN; charset=US-ASCII
>
> I have released two new sp add-on packages on the r-spatial  
> repository.
>
> Rgshhs converts GSHHS shorelines (as closed polygons) to sp class
> SpatialPolygons, which can then be written out as shapefiles for the
> chosen region. It's now very slow for full resolution, because  
> clipping
> the largest land polygons takes a lot of time, but hopefully people  
> don't
> do that every time they need data. It is provided with the coarse  
> dataset,
> but works with the full and the others. It leaves the longitude
> coordinates in the -20 to 360 range like the data source. Details  
> of the
> Global Self-consistent, Hierarchical, High-resolution Shoreline  
> Database
> are avialable from:
>
> http://www.soest.hawaii.edu/wessel/gshhs/gshhs.html
>
> where the low, intermediate, high, and full resolution data may be
> downloaded from. I'd be grateful for ideas for making it faster,  
> and am
> looking at providing indices of which level polygons are included in
> next-level polygons preprocessed in the package rather than  
> computing them
> each time for chosen polygons.
>
> A second package is spspatstat, providing interfaces between some sp
> classes and the well-supported point pattern analysis package  
> spatstat.
> The spatstat ppp and owin classes are matched with sp equivalents.
>
> To get a feel for where sp is going, (and after installing sp and
> spatstat from CRAN with their dependencies, and the new packages from
> http://r-spatial.sourceforge.net/R), try:
>
> library(Rgshhs)
> library(spspatstat)
> gshhs.c.b <- system.file("share/gshhs_c.b", package = "Rgshhs")
> NZx <- c(160, 180)
> NZy <- c(-50, -30)
> NZ <- Rgshhs(gshhs.c.b, xlim = NZx, ylim = NZy)
> plot(runifpoint(500, as(NZ$SP, "owin")))
>
> Hoping for feedback,
>
> Roger
>
> -- 
> Roger Bivand
> Economic Geography Section, Department of Economics, Norwegian  
> School of
> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
>
>
>
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> End of R-sig-Geo Digest, Vol 26, Issue 12
> *****************************************
>