adapting spatial points and wrld_smpl to a reference system implicit in a .nc file

This looks like WRF <http://www.wrf-model.org/index.php> data. I just
dealt with this.
The data is on a sphere as opposed to WGS84 so you need +ellps=sphere
+a=6370000 +b=6370000 +units=m

+proj=lcc which is usually what wrf is run with.
The tricky part is:
+lat_1=25.0 +lat_2=45.0 +lat_0=38.0 +lon_0=-100.0
because every WRF run is different (the WRF Preprocessing System optimizes
the projection for the domain).
and then there is probably no shift so you need(?) +x_0=0 +y_0=0

This gives:
+proj=lcc +lat_1=25.0 +lat_2=45.0 +lat_0=38.0 +lon_0=-100.0 +ellps=sphere
+a=6370000 +b=6370000 +units=m +no_defs

But, wrf users like to give out lat and  long so you need to assign it:
+proj=longlat +ellps=sphere +a=6370000 +b=6370000 +units=m +no_defs

and then reproject the lat/long to lcc coordinates using this string:
+proj=lcc +lat_1=25.0 +lat_2=45.0 +lat_0=38.0 +lon_0=-100.0 +ellps=sphere
+a=6370000 +b=6370000 +units=m +no_defs

One word of caution, make sure you received the correct coordinates. Some
variables are run cell center while some are run at cell edge. It looks
like from your .nc file it was made by your collaborator so I assume they
are right.

That said, another word of caution, I found that the XLAT and XLONG
variables from WRF output aren't very precise. There is a "geogrid" file
from the preprocessing system that has the domain corners, resolution, nrow
and ncol from which you can make a better grid using the native projection
system (in my case it was a 4km grid). I suggest you try to get those.

I hope this helps... I have to run but wanted to save people too much head
scratching. I can get you running with more help tonight if you need.
Dominik


On Tue, Feb 23, 2016 at 11:27 AM, Agus Camacho <agus.camacho at gmail.com>
wrote:

Thanks heaps to all for your effort. If I go to another GEOSTAT ill bring
more giant crab this time.

The creator of the .nc file also looked at this webpage:
http://www.pkrc.net/wrf-lambert.html
It seemed like the right proj4 string might be this one:

+proj=lcc +lat_1=25.0 +lat_2=45.0 +lat_0=38.0
    +lon_0=-100.0 +a=6370 +b=6370 +towgs84=0,0,0 +no_defs

However this projection also does not allow me to adequately plot the
locations on the raster.

Here is the .nc file. it contains several layers.


https://www.dropbox.com/s/yto3linsgom3zi7/results_us_future_output_none_0.nc?dl=0



2016-02-23 2:25 GMT-07:00 Michael Sumner <mdsumner at gmail.com>:

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 T?gersen 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 T?gersen
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

--
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

--
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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--
Agust?n Camacho Guerrero.
Doutor em Zoologia.
Laborat?rio de Herpetologia, Departamento de Zoologia, Instituto de
Bioci?ncias, USP.
Rua do Mat?o, trav. 14, n? 321, Cidade Universit?ria,
S?o Paulo - SP, CEP: 05508-090, Brasil.

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