[R-sig-Geo] adapting spatial points and wrld_smpl to a reference system implicit in a .nc file

Michael Sumner mdsumner at gmail.com
Tue Feb 23 10:25:41 CET 2016 

On Tue, 23 Feb 2016 at 20:09 Roger Bivand <Roger.Bivand at nhh.no> wrote:

> On Tue, 23 Feb 2016, Alex Mandel wrote:
>
> > I made an attempt at it too. Investigating the original data, I'm not
> > sure that the projection information supplied is correct for the data
> > linked. When I load up the data in a unprojected space, the coordinates
> > don't look at all similar to any Lambert projected data I have, they
> > actually look like Lat/Lon in some unprojected coordinate system,
> > perhaps a different spheroid than expected.
>
> Does anyone have a link to the original data? Is is possible that this is
> the General Oblique Transformation used by modellers - that is something
> that feels like longlat but is recentred and oblique? Example at the very
> end of my GEOSTAT talk last year (slides 81-83):
>
> http://geostat-course.org/system/files/geostat_talk_150817.pdf
>
> Roger
>
>
For what it is worth, the General Oblique Transformation is not the only
example - it's very common for modellers to have a mesh that has the
"mostly-properties" of a projection, but is not actually describable with
standard transform + affine parameters. The main cases that I've seen are
polar stereographic, equal area or oblique Mercator. Often they really are
simple transforms and you can reconstruct without loss, but it's not
usually possible to tell without exploration. It's an interesting
dis-connect to see code that builds a mesh with certain properties, then
only stores longitudes and latitudes - when it could be done with standard
tools and be stored and used much more efficiently.

(I've seen Lambert Conformal Conic and Lambert Azimuthal Equal Area
terminology conflated in this context too. )

I'm also interested to explore the original data.

Cheers, Mike.



> >
> > -Alex
> >
> > On 02/22/2016 10:17 PM, Frede Aakmann Tøgersen wrote:
> >> Hi
> >>
> >> I tried to make it work but I had to give up. I wanted to reproject the
> Lamberth conformal conic coordinates to long-lat but it didn't work.
> >>
> >> Perhaps someone can see what I did wrong. Here is what I did (data in R
> binary format and figure in png format both attached):
> >>
> >> library(raster)
> >> library(maptools)
> >> data(wrld_simpl)
> >>
> >> r <- raster("raster.grd")
> >> projection(r)
> >> ## > NA
> >>
> >> uro <- read.table("clean urosaurus records.csv", h = TRUE, sep = ",")
> >> coordinates(uro) <- ~lon+lat
> >>
> >> ## Set projections for the 3 data sets
> >>
> >> ## Lamberth's confocal conic projection with given parameters
> >> crs(r) <- "+proj=lcc +lat_0=38.0 +lon_0=-100 +lat_1=25.0 +lat_2=45.0
> +ellps=WGS84"
> >> projection(r)
> >>
> >> ## Assume that lon, lat are geographical coordinates (degrees decimal)
> >> proj4string(uro) <- CRS("+proj=longlat +datum=WGS84")
> >>
> >> ## wrld_simpl is in geographical coordinates
> >> proj4string(wrld_simpl)
> >>
> >> ## Make figure in png format
> >> ## Of course plotting data with 2 different projections will give
> >> ## some distortions
> >> pdf("uro.png")
> >>
> >> plot(r)
> >> points(uro)
> >> plot(wrld_simpl, add = TRUE) # World will be clipped to extent of 'r'
> >>
> >> dev.off()
> >>
> >> extent(r)
> >> ## class       : Extent
> >> ## xmin        : -131.4368
> >> ## xmax        : -68.56323
> >> ## ymin        : 12.35567
> >> ## ymax        : 50.26619
> >>
> >> ## Reproject the raster to long-lat
> >> ## This doesn't work (collapsed domain)
> >> rp <- projectRaster(r, crs = "+proj=longlat +datum=WGS84 +no_defs
> +ellps=WGS84 +towgs84=0,0,0")
> >>
> >> ## Because
> >>> extent(rp)
> >> ## class       : Extent
> >> ## xmin        : -100.0015
> >> ## xmax        : -99.68557
> >> ## ymin        : 37.70658
> >> ## ymax        : 38.00046
> >>
> >> ## Save data in R binary format
> >> save(list = c("r", "uro", "wrld_simpl"), file = "uro.RData")
> >>
> >>
> >> Yours sincerely / Med venlig hilsen
> >>
> >> Frede Aakmann Tøgersen
> >> Specialist, M.Sc., Ph.D.
> >> Plant Performance & Modeling
> >>
> >> Technology & Service Solutions
> >> T +45 9730 5135
> >> M +45 2547 6050
> >> frtog at vestas.com
> >> http://www.vestas.com
> >>
> >> Company reg. name: Vestas Wind Systems A/S
> >> This e-mail is subject to our e-mail disclaimer statement.
> >> Please refer to www.vestas.com/legal/notice
> >> If you have received this e-mail in error please contact the sender.
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: R-sig-Geo [mailto:r-sig-geo-bounces at r-project.org] On Behalf Of
> Agus Camacho
> >> Sent: 22. februar 2016 19:20
> >> To: tech at wildintellect.com
> >> Cc: r-sig-geo
> >> Subject: Re: [R-sig-Geo] adapting spatial points and wrld_smpl to a
> reference system implicit in a .nc file
> >>
> >> Thanks Alex, but the locations still fall in the sea when i plot them
> using
> >> your recommended Solution. I looked at the sites you proposed and they
> have
> >> other values for lat_1, lat_0, etc..
> >>
> >> 2016-02-22 11:04 GMT-07:00 Alex M <tech_dev at wildintellect.com>:
> >>
> >>> On 02/22/2016 09:50 AM, Agus Camacho wrote:
> >>>> Dear all,
> >>>>
> >>>> Im trying to overlap these points:
> >>>>
> >>>
> https://www.dropbox.com/s/awdclg4cvsdngej/clean%20urosaurus%20records.csv?dl=0
> >>>>
> >>>> and a wrld_simpl object:
> >>>> library(maptools)
> >>>> data(wrld_simpl)
> >>>>
> >>>> Over this raster layer
> >>>>
> >>>
> https://www.dropbox.com/sh/qcw174tgogpnz7s/AAByDc3TeyFe3W4nEqTFix6Oa?dl=0
> >>>>
> >>>> This rastr comes from a .nc file without a reference system. The
> author
> >>> of
> >>>> that .nc file gave me the following data about the .nc.
> >>>>
> >>>> The projection is *Lambert conformal conic* projection
> >>>> CEN_LAT = 38.0
> >>>> CEN_LON = -100.0
> >>>> TRUELAT1 = 25.
> >>>> TRUELAT2 = 45.
> >>>>
> >>>> However, despite i have gone through many sites in the internet, i
> cant
> >>>> figure it out:
> >>>>
> >>>> a) if that is all the data i need to set a reference system for my
> points
> >>>> and the wrld_simp object.
> >>>>
> >>>> b) how to change a typical CRS object with such data
> >>>>
> >>>> Ex.CRS ("+proj=lcc+lat_0=38.0+lon0_2=-100+ellps=WGS84")
> >>>>
> >>>> Where do i enter the TRUELAT and CENLAT values?
> >>>> Are there any site that explains easily what the fields in the CRS
> mean
> >>> and
> >>>> how to change them?
> >>>>
> >>>> Thanks in advance.
> >>>>
> >>>
> >>> https://github.com/OSGeo/proj.4/wiki/GenParms
> >>> https://trac.osgeo.org/proj/wiki/GenParms
> >>>
> >>> I believe:
> >>> +lat_0  = CEN_LAT   Latitude of origin
> >>> +lat_1  = TRUELAT1   Latitude of first standard parallel
> >>> +lat_2  = TRUELAT2   Latitude of second standard parallel
> >>> +lon_0  = CEN_LON   Central meridian
> >>>
> >>> proj strings are defined by the proj4 libary. It's website listed above
> >>> and the associated mailing lists or gis stackexchange would be the
> >>> places to get help on it.
> >>> https://lists.osgeo.org/mailman/listinfo/metacrs
> >>>
> >>> It often helps to browse similar projections on
> >>> http://spatialreference.org/
> >>> http://epsg.io/
> >>>
> >>> Enjoy,
> >>> Alex
> >>>
> >>>
> >>
> >>
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo at r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
> --
> Roger Bivand
> Department of Economics, Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; fax +47 55 95 91 00
> e-mail: Roger.Bivand at nhh.no
> http://orcid.org/0000-0003-2392-6140
> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
> http://depsy.org/person/434412
> _______________________________________________
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-- 
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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