Matthew Landis | 12 Jul 14:39 2010

T62 Gaussian grid

Dear Proj list,

I'm trying to incorporate some climate data into a model.  Most of our 
data is on a regular lat-lon grid, but the climate data uses a T62 
Gaussian grid.  I'm new to these; apparently they are commonly used in 
climate models (see http://en.wikipedia.org/wiki/Gaussian_grid). The 
distinguishing feature is that they are not regular grids in that the 
size of the latitude grid cells varies with latitude.   I'd like to be 
able to interpolate them to a regular grid (I'm working in R using 
rgdal), but I haven't been able to find a proj.4 string to help specify 
the interpolation. 

In the meantime, I have  a workaround by simply changing the latitude 
coordinates at the poles slightly to fit on a regular grid.  This should 
be OK, but for the sake of appearances I'd like to do it the proper way.

Many thanks for any thoughts. 

Sincerely,

Matt

--

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~
Matthew Landis, Ph.D.
Research Scientist
ISciences, LLC
61 Main St. Suite 200
Burlington VT 05401
802.864.2999
(Continue reading)

Karney, Charles | 13 Jul 23:36 2010

Wallis 1 transverse Mercator

> From: strebe <at> aol.com
> Sent: Sunday, February 01, 2009 04:23
> 
> I've posted here and image of yet another ellipsoidal transverse
> Mercator variation:
>      http://www.mapthematics.com/Wallis1TransverseMercator.tif
> 
> This one's properties are:
>      Conformal (of course)
>      Straight central meridian (of course)
>      Parallels are equally spaced.
> 
> The importance of this last property is that the projection then may
> be squeezed through the rectifying latitude calculation as applied to
> the complex plane, and out pops Gauß-Krüger. I generated the map using
> the same eccentricity in your examples so that the 81st meridian (and
> 99th) will run into the singularities. The graticule is 9°. The
> projection is cropped at a distance of 4 arc seconds around the
> singularities; in point of fact the projection is infinite in extent.

There's a depiction of your "Wallis 1" projection in

    R. Koenig and K. H. Weise,
    Mathematische Grundlagen der Hoeheren Geodaesie und Kartographie,
    (Springer-Verlag, 1951), Vol 1.

See figure 16b on page 88.  They call this the "complex latitude plane"
(B-Ebene).

	--Charles
(Continue reading)

strebe | 15 Jul 03:56 2010
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Re: Wallis 1 transverse Mercator


Charles:

Thank you very much for this reference, which I had not heard of. Now I can be less surprised that the variant has been overlooked! I will add the “complex latitude transverse Mercator” as a synonym in Geocart’s literature and try to acquire a copy of the paper.

Regards,
— daan Strebe


On Jul 13, 2010, at 2:36:48 PM, "Karney, Charles" <ckarney <at> Sarnoff.com> wrote:

From: "Karney, Charles" <ckarney <at> Sarnoff.com>
Subject: Wallis 1 transverse Mercator
Date: July 13, 2010 2:36:48 PM PDT
To: "PROJ.4 and general Projections Discussions" <proj <at> lists.maptools.org>, "strebe <at> aol.com" <strebe <at> aol.com>
> From: strebe <at> aol.com > Sent: Sunday, February 01, 2009 04:23 > > I've posted here and image of yet another ellipsoidal transverse > Mercator variation: > http://www.mapthematics.com/Wallis1TransverseMercator.tif > > This one's properties are: > Conformal (of course) > Straight central meridian (of course) > Parallels are equally spaced. > > The importance of this last property is that the projection then may > be squeezed through the rectifying latitude calculation as applied to > the complex plane, and out pops Gauß-Krüger. I generated the map using > the same eccentricity in your examples so that the 81st meridian (and > 99th) will run into the singularities. The graticule is 9°. The > projection is cropped at a distance of 4 arc seconds around the > singularities; in point of fact the projection is infinite in extent. There's a depiction of your "Wallis 1" projection in R. Koenig and K. H. Weise, Mathematische Grundlagen der Hoeheren Geodaesie und Kartographie, (Springer-Verlag, 1951), Vol 1. See figure 16b on page 88. They call this the "complex latitude plane" (B-Ebene). --Charles -- Charles Karney <ckarney <at> sarnoff.com> Sarnoff Corporation, Princeton, NJ 08543-5300 Tel: +1 609 734 2312 Fax: +1 609 734 2662

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Hailey Eckstrand | 21 Jul 22:12 2010
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proj4 definition for transverse mercator projection from RegCM3 model for North America

Hello all,
I am trying to create the proj4 string for a netcdf file with the following coordinate information:

variables:
        char Transverse_Mercator ;
                Transverse_Mercator:grid_mapping_name = "transverse_mercator" ;
                Transverse_Mercator:longitude_of_central_meridian = -97. ;
                Transverse_Mercator:latitude_of_projection_origin = 47.5 ;
                Transverse_Mercator:scale_factor_at_central_meridian = 1. ;
                Transverse_Mercator:false_easting = 3925000. ;
                Transverse_Mercator:false_northing = 3175000. ;
        double lat(yc, xc) ;
                lat:units = "degrees_north" ;
                lat:long_name = "latitude" ;
                lat:standard_name = "latitude" ;
                lat:axis = "Y" ;
        double lon(yc, xc) ;
                lon:units = "degrees_east" ;
                lon:long_name = "longitude" ;
                lon:standard_name = "longitude" ;
                lon:axis = "X" ;
        double xc(xc) ;
                xc:long_name = "x-coordinate in Cartesian system" ;
                xc:standard_name = "projection_x_coordinate" ;
                xc:units = "m" ;
                xc:axis = "X" ;
        double yc(yc) ;
                yc:long_name = "y-coordinate in Cartesian system" ;
                yc:standard_name = "projection_y_coordinate" ;
                yc:units = "m" ;
                yc:axis = "Y" ;


The file gives the coordinates in their native projected coordinates as well as the lat & lon coordinates.

From this information, I created the following proj4 string:
+proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97.0 +k_0=1.0 +units=m +ellps=sphere

(The sphere ellipsoid is a guess as they didn't provide the geographic coordinate system.)
So when I test out this proj4 string, these are the results I get:

proj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97.0 +k_0=1.0 +units=m +ellps=sphere
in> -126.0869 19.61229
in> -125.6792 19.77242
in> -125.2703 19.93048

out> 773317.154904   359897.643377
out> 824089.485710   370794.986195
out> 874706.342446   381466.440468

the projection coordinates should be:
600000   600000
650000   600000
700000   600000

and then the opposite transformation:

invproj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=263 +k_0=1.0 +ellps=sphere
in>  600000 600000
in>  650000 600000
in>  700000 600000

out>  -127.929260     -21.210147
out>  -127.514502     -21.293413
out>  -127.097731     -21.375966

and the coordinates should be:
-126.0869 19.61229
-125.6792 19.77242
-125.2703 19.93048

The longitude are at least in the ballpark, but the latitudes are completely off.

If it helps, this data has been downloaded from NARCCAP, and it is the RegCM3 model.
Any help would really be appreciated.
Thanks in advance,
Hailey



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support.mn | 22 Jul 09:51 2010
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Re: proj4 definition for transverse mercator projection from RegCM3 model for North America

Hello,

You have different lon_0 ??!!

fwd: +lon_0=-97.0
inv: +lon_0=263

Are you sure your parameters are correct??

Regards: Janne.

=====================================

Hailey Eckstrand [haileyeckstrand <at> gmail.com] kirjoitti: 
> Hello all,
> I am trying to create the proj4 string for a netcdf file with the following
> coordinate information:
> 
> variables:
>         char Transverse_Mercator ;
>                 Transverse_Mercator:grid_mapping_name =
> "transverse_mercator" ;
>                 Transverse_Mercator:longitude_of_central_meridian = -97. ;
>                 Transverse_Mercator:latitude_of_projection_origin = 47.5 ;
>                 Transverse_Mercator:scale_factor_at_central_meridian = 1. ;
>                 Transverse_Mercator:false_easting = 3925000. ;
>                 Transverse_Mercator:false_northing = 3175000. ;
>         double lat(yc, xc) ;
>                 lat:units = "degrees_north" ;
>                 lat:long_name = "latitude" ;
>                 lat:standard_name = "latitude" ;
>                 lat:axis = "Y" ;
>         double lon(yc, xc) ;
>                 lon:units = "degrees_east" ;
>                 lon:long_name = "longitude" ;
>                 lon:standard_name = "longitude" ;
>                 lon:axis = "X" ;
>         double xc(xc) ;
>                 xc:long_name = "x-coordinate in Cartesian system" ;
>                 xc:standard_name = "projection_x_coordinate" ;
>                 xc:units = "m" ;
>                 xc:axis = "X" ;
>         double yc(yc) ;
>                 yc:long_name = "y-coordinate in Cartesian system" ;
>                 yc:standard_name = "projection_y_coordinate" ;
>                 yc:units = "m" ;
>                 yc:axis = "Y" ;
> 
> 
> The file gives the coordinates in their native projected coordinates as well
> as the lat & lon coordinates.
> 
> From this information, I created the following proj4 string:
> +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97.0 +k_0=1.0
> +units=m +ellps=sphere
> 
> (The sphere ellipsoid is a guess as they didn't provide the geographic
> coordinate system.)
> So when I test out this proj4 string, these are the results I get:
> 
> proj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0
> +lon_0=-97.0 +k_0=1.0 +units=m +ellps=sphere
> in> -126.0869 19.61229
> in> -125.6792 19.77242
> in> -125.2703 19.93048
> 
> out> 773317.154904   359897.643377
> out> 824089.485710   370794.986195
> out> 874706.342446   381466.440468
> 
> the projection coordinates should be:
> 600000   600000
> 650000   600000
> 700000   600000
> 
> and then the opposite transformation:
> 
> invproj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0
> +lon_0=263 +k_0=1.0 +ellps=sphere
> in>  600000 600000
> in>  650000 600000
> in>  700000 600000
> 
> out>  -127.929260     -21.210147
> out>  -127.514502     -21.293413
> out>  -127.097731     -21.375966
> 
> and the coordinates should be:
> -126.0869 19.61229
> -125.6792 19.77242
> -125.2703 19.93048
> 
> The longitude are at least in the ballpark, but the latitudes are completely
> off.
> 
> If it helps, this data has been downloaded from NARCCAP, and it is the
> RegCM3 model.
> Any help would really be appreciated.
> Thanks in advance,
> Hailey
> 
> _______________________________________________
> Proj mailing list
> Proj <at> lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/proj

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Hailey Eckstrand | 22 Jul 18:32 2010
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Re: proj4 definition for transverse mercator projection from RegCM3 model for North America

Hi,
Looks like I pasted in the wrong statement. Sorry! I was just testing out
different ideas. It doesn't make a different though, as lon_0=-97 & lon_0=263
both output the same result:

proj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97.0
+k_0=1.0 +units=m +ellps=sphere
in> -126.0869 19.61229
in> -125.6792 19.77242
in> -125.2703 19.93048

out> 773317.154904   359897.643377
out> 824089.485710   370794.986195
out> 874706.342446   381466.440468

proj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=263
+k_0=1.0 +units=m +ellps=sphere
in> -126.0869 19.61229
in> -125.6792 19.77242
in> -125.2703 19.93048

out> 773317.154904   359897.643377
out> 824089.485710   370794.986195
out> 874706.342446   381466.440468

invproj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=263
+k_0=1.0 +ellps=sphere 
in> 600000 600000
in> 650000 600000
in> 700000 600000

out> -127.929260     -21.210147
out> -127.514502     -21.293413
out> -127.097731     -21.375966

invproj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97
+k_0=1.0 +ellps=sphere 
in> 600000 600000
in> 650000 600000
in> 700000 600000

out> -127.929260     -21.210147
out> -127.514502     -21.293413
out> -127.097731     -21.375966

Hailey 

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support.mn | 23 Jul 23:52 2010
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Re: proj4 definition for transverse mercator projection from RegCM3 model for North America

Hello,

> The sphere ellipsoid is a guess as they didn't provide the geographic coordinate system

check your parameters, especially if the assumption about the sphere is correct and if the
sphere is of a right size? Test with the normal NAD83, NAD27, WGS84 datums with their
correct ellipsoids Clarke 1866,  GRS 80 and WGS84 etx.

http://en.wikipedia.org/wiki/North_American_Datum

http://en.wikipedia.org/wiki/World_Geodetic_System

Janne.

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Melita Kennedy | 26 Jul 02:28 2010
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Re: proj4 definition for transverse mercator projection from RegCM3 model for North America


-----Original Message-----

>Date: Sat, 24 Jul 2010 00:52:37 +0300 (EEST)
>From: support.mn <at> elisanet.fi
>Subject: Re: [Proj] proj4 definition for transverse mercator
>	projection from RegCM3 model for North America
>To: "PROJ.4 and general Projections Discussions"
>	<proj <at> lists.maptools.org>
>
>Hello,
>
>> The sphere ellipsoid is a guess as they didn't provide the geographic coordinate system
>
>check your parameters, especially if the assumption about the sphere is correct and if the
>sphere is of a right size? Test with the normal NAD83, NAD27, WGS84 datums with their
>correct ellipsoids Clarke 1866,  GRS 80 and WGS84 etx.
>
>http://en.wikipedia.org/wiki/North_American_Datum
>
>http://en.wikipedia.org/wiki/World_Geodetic_System
>
>Janne.

I just looked through some of the RegCM3 source code. I did find a 6371229.0 value in the projection section
of terrain.f. It doesn't list transverse Mercator as an option, rather it's a rotated (oblique)
Mercator. The equations for this and the other projections are definitely sphere-based with no sign that
the incoming terrain data (ex. USGS LULC) is being converted from the ellipsoid-based datum to the
sphere. 

Melita

Melita
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Nikos Gerontidis | 27 Jul 08:39 2010
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transformation wrong results from ESPG:4326 to ESPG:2100


Hello list

I want to transform coordinates from a projection with ESPG:4326 to
a projection ESPG:2100, but some problems exist. In more details I am trying to
use the proj4 library so the problem is related with function : pj_transform(..) :

Here are the parameters used for ESPG:2100

ESPG: 2100----->  "+proj=tmerc +lat_0=0 +lon_0=24 +k=0.999600 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs "
ESPG:4326------> "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs "

Code is included inside the attached file.

the projection parameters are a copy paste from PostGis.
And another thing, is it possible to use directly the ESPG codes  inside pj_transform("Something like+ESPG:2100","ESPG:4326")

Any ideas? Am I doing something wrong?
Thanks in advance.

--
Best Regards
Nikos Gerontidis
char *params[] = { "proj=merc", "lat_0=0", "lon_0=24", "k=0.999600", "x_0=500000", "y_0=0",
"ellps=GRS80", "towgs84=-199.87,74.79,246.62,0,0,0,0", "units=m", "no_defs"};

if (!(pj_merc = pj_init(3,params)))
	return;
if (!(pj_latlong = pj_init_plus("+proj=latlong +ellps=WGS84 +datum=WGS84 +no_defs")))
	return;
double x = 0.69241249012994599;
double y = 0.39130891160970277;

qint32 code = pj_transform(pj_latlong, pj_merc, 1, 1, &x, &y, NULL );

// Output coordinates

// x equals to 1744633.9435213772
// y equals to 2545764.3957969979

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nicolas david | 27 Jul 09:18 2010
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Re: transformation wrong results from ESPG:4326 to ESPG:2100

Hello

1-) about your code :

char *params[] = { "proj=merc", "lat_0=0", "lon_0=24", "k=0.999600", "x_0=500000", "y_0=0", "ellps=GRS80", "towgs84=-199.87,74.79,246.62,0,0,0,0", "units=m", "no_defs"};

if (!(pj_merc = pj_init(3,params)))
return;
I think that "3" is a wrong argument, in your case it must be "11", the number of argument that your params variable contains.

2-) to use EPSG code you could use pj_init_plus and the "+init" parameters.

if (! (pj_merc = pj_init_plus("+init=EPSG:2100") ) ) return ;



Nicolas DAVID

2010/7/27 Nikos Gerontidis <geronik444 <at> gmail.com>

Hello list

I want to transform coordinates from a projection with ESPG:4326 to
a projection ESPG:2100, but some problems exist. In more details I am trying to
use the proj4 library so the problem is related with function : pj_transform(..) :

Here are the parameters used for ESPG:2100

ESPG: 2100----->  "+proj=tmerc +lat_0=0 +lon_0=24 +k=0.999600 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs "
ESPG:4326------> "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs "

Code is included inside the attached file.

the projection parameters are a copy paste from PostGis.
And another thing, is it possible to use directly the ESPG codes  inside pj_transform("Something like+ESPG:2100","ESPG:4326")

Any ideas? Am I doing something wrong?
Thanks in advance.

--
Best Regards
Nikos Gerontidis

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Gmane