On Wed, 25 Feb 2009, Roger Bivand wrote:
On Tue, 24 Feb 2009, Martin Maechler wrote:
"RB" == Roger Bivand <roger.biv...@nhh.no>
on Fri, 20 Feb 2009 09:55:52 +0100 (CET) writes:
RB> On Wed, 18 Feb 2009, Greg Snow wrote:
>> There is a shapefile (works well with maptools and sp packages) with
a
>> world map and time zone information at:
>> http://openmap.bbn.com/data/shape/timezone/
>>
>> It has the info needed to color the countries or parts of countries
>> based on time zone, but does not have polygons for time zone stripes
>> over the oceans.
RB> In fact, this shapefile provoked an update in sp, because it is
really
RB> buggy.
I'm happy to have provoked progress ;-) :-)
RB> There are straight-line polygons and many others have multiple
RB> repeated coordinates (the sp update fixes these to retain finite
label
RB> points), but it doesn't fix the absence of most of the data (several
DBF
RB> columns are empty - checked in oocalc):
>> library(rgdal)
>> tz <- readOGR(".", "WrldTZA")
RB> OGR data source with driver: ESRI Shapefile
RB> Source: ".", layer: "WrldTZA"
RB> with 1890 rows and 11 columns
RB> Feature type: wkbPolygon with 2 dimensions
RB> Warning messages:
RB> 1: In Polygon(cbind(jG[[1]], jG[[2]])) :
RB> Non-finite label point detected and replaced
RB> 2: In Polygon(cbind(jG[[1]], jG[[2]])) :
RB> Non-finite label point detected and replaced
RB> 3: In Polygon(cbind(jG[[1]], jG[[2]])) :
RB> Non-finite label point detected and replaced
>> names(tz)
RB> [1] "FIPS" "NAME" "COMMENTS" "REGION" "LAT" "LON"
RB> [7] "TZ" "GMTOFF" "LOCALSUM" "OFFSET" "CLASSES"
>> summary(tz$GMTOFF)
RB> NA's
RB> 1890
>> summary(tz$TZ)
RB> NA's
RB> 1890
>> summary(tz$OFFSET)
RB> 0 \xff0 -1 \xff-1 \xff+1 -10 +10
RB> 25 57 13 7 181 24 38
RB> \xff+10 +10.5 +11 +11.5 +12 \xff+12 +2
RB> 24 1 19 3 12 13 1
RB> \xff-2 \xff+2 +3 \xff-3 \xff+3 -3.5 \xff+3.5
RB> 4 90 59 146 25 7 3
RB> -4 +4 \xff-4 \xff+4 \xff+4.5 -5 +5
RB> 56 4 165 8 1 130 13
RB> \xff-5 \xff+5 \xff+5.5 \xff+5.75 -6 +6 \xff-6
RB> 12 3 16 1 77 10 16
RB> \xff+6 \xff+6.5 -7 +7 \xff+7 -8 +8
RB> 12 15 63 98 14 61 68
RB> \xff-8 \xff+8 -9 +9 \xff+9 +9.5 NA's
RB> 3 56 82 97 13 11 33
RB> where my locale is UTF-8.
RB> I wrote to Martin offline that a more recent link is:
RB> http://efele.net/maps/tz/world/
RB> and I've put tz_world.rda on http://spatial.nhh.no/R/etc, but it is
not
RB> line generalised, so it is very large and takes a long time to
display -
RB> they've kept a lot of boundary detail.
indeed. But thanks a lot to make it available!!
RB> Because TZ follow administrative boundaries, they are actually hard
to do
RB> right. Maybe a raster version might help more if vector precision
isn't
RB> needed?
as long as we can add a couple of cities (using geographical
coordinates) to it, afterwards, that's fine.
When I load your (above URL) tz file and plot it,
I get the impression that much time is spent on thousands of
very small polygons;
consequently, if I'd want a ``subset'' of tz that only contains
the polygons that correspond to areas larger than, say, 100 km^2,
how could I do that ?
I've put simpl_tz.rda on the same site with the smaller non-principal islands
removed, so it plots faster. However, attempts to do line simplification to
reduce the detail on coastlines have not yet succeeded.
Anyone like to try to do the line simplification? In GRASS, I'm seeing
"Attempt to read dead line" after both v.generalize and v.simplify.
Compared to the original object, this one has very many fewer constituent
Polygons objects, because all the geometries with the same time zone have
been collected into single Polygons objects, rather than being almost all
singletons. This has also speeded up plotting.
And a raster version, same site, SGDF_tz.rda. Then:
image(SGDF, "tzn", col=rainbow(300))
plots a map.
Roger
Hope this helps,
Roger
Looking at the sp-object:
------------------------------------------------------------------------
load("tz_world.rda")
## Look a bit at the 'tz' object:
str(tz, max=2)
## Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
## ..@ data :'data.frame': 27704 obs. of 1 variable:
## .. ..- attr(*, "data_types")= chr "C"
## ..@ polygons :List of 27704
## ..@ plotOrder : int [1:27704] 24471 111 14349 24641 1598 10291 22351
...
## ..@ bbox : num [1:2, 1:2] -180 -90 180 83.6
## .. ..- attr(*, "dimnames")=List of 2
## ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
ltz <- sapply(slotNames(tz), slot, object=tz)
sapply(ltz, object.size)
## data polygons plotOrder bbox proj4string
## 1690424 110706296 110856 704 704
str(t...@data[,1])
## Factor w/ 382 levels "Africa/Abidjan",..: 307 307 307 307 307 307 ...
str(head(t...@polygons[1:3]), max=1)
## List of 3
## $ :Formal class 'Polygons' [package "sp"] with 5 slots
## $ :Formal class 'Polygons' [package "sp"] with 5 slots
## $ :Formal class 'Polygons' [package "sp"] with 5 slots
------------------------------------------------------------------------
and then ask for
showMethods(class = "Polygons")
the result is not so revealing to me; but of course, I'm really
an sp greenhorn.
How could I compute areas?
Regards,
Martin
RB> Roger
>>
>> Hope this helps,
>>
>>
RB> --
RB> Roger Bivand
RB> Economic Geography Section, Department of Economics, Norwegian
School of
RB> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
RB> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
RB> e-mail: roger.biv...@nhh.no
--
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.biv...@nhh.no
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