[GRASS-user] adding a datum to the GRASS database

GRASS GRASS user
1

Hi all -
I’m brand new to GRASS (though have basic familiarity with ArcInfo). I work in a datum that apparently isn’t contained in the basic GRASS library – from what I’ve uncovered searching this list & the general web, I need to add my datum by going to the $GISBASE/etc/datum.table and appending this text:

The Arc 1960 datum; source: EPSG database
arc60 “Arc 1960” clark80 dx=-160 dy=-6 dz=-302

However, I have no idea how to find this. Using both my Mac Finder as well as my very rudimentary bash skills, I navigated to the GRASS/6.4/Modules/etc/ folder, but see only a filed called xtnmenu.dat (which I don’t know how to open).

Can anyone provide some very basic instructions for how to do this?

Thanks so much!

ali

2

Hi Ali,

On Fri, Nov 16, 2012 at 9:05 PM, Ali Swanson <swanson.ali@gmail.com> wrote:

Hi all -
I'm brand new to GRASS (though have basic familiarity with ArcInfo).

welcome :slight_smile:

I work
in a datum that apparently isn't contained in the basic GRASS library --
from what I've uncovered searching this list & the general web, I need to
add my datum by going to the $GISBASE/etc/datum.table and appending this
text:

The Arc 1960 datum; source: EPSG database
arc60 "Arc 1960" clark80 dx=-160 dy=-6 dz=-302

Which EPSG code is that? EPSG 4210, this one?

epsg_tr -pretty_wkt 4210
GEOGCS["Arc 1960",
    DATUM["Arc_1960",
        SPHEROID["Clarke 1880 (RGS)",6378249.145,293.465,
            AUTHORITY["EPSG","7012"]],
        TOWGS84[-160,-6,-302,0,0,0,0],
        AUTHORITY["EPSG","6210"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4210"]]

It should be there. You can use the Location Wizard to select this
EPSG code.

BUT: I just tried and the datum is not recognised:

g.proj -w
GEOGCS["clark80",
    DATUM["unknown",
        SPHEROID["Clarke_1880",6378249.145,293.465]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433]]

Do these tickets strike back?
http://trac.osgeo.org/grass/ticket/1452
http://trac.osgeo.org/grass/ticket/1748

Markus

3

Hi Markus -
Thanks for your prompt reply. Unfortunately, I think that my GRASS skills are faaaar below those of most other users. (I don’t even know how to find the datum.table file to which I thought I was supposed to add the ARC1960 datum, or really understand your suggestions.) But! From your advice I was able to (I think) select the proper Arc1960 datum. I have done everything so far with the graphical interface, and was trying to select the Arc1960 (using location wizard) from the first menu choice (selecting from a list of coordinate system parameters) – when I chose the second menu option (select EPGS code of spatial reference system), I believe I found it. Pretty basic, in the end. Thanks again!

···

On Sat, Nov 17, 2012 at 5:54 AM, Markus Neteler <neteler@osgeo.org> wrote:

Hi Ali,

On Fri, Nov 16, 2012 at 9:05 PM, Ali Swanson <swanson.ali@gmail.com> wrote:

Hi all -
I’m brand new to GRASS (though have basic familiarity with ArcInfo).

welcome :slight_smile:

I work
in a datum that apparently isn’t contained in the basic GRASS library –
from what I’ve uncovered searching this list & the general web, I need to
add my datum by going to the $GISBASE/etc/datum.table and appending this
text:

The Arc 1960 datum; source: EPSG database
arc60 “Arc 1960” clark80 dx=-160 dy=-6 dz=-302

Which EPSG code is that? EPSG 4210, this one?

epsg_tr -pretty_wkt 4210
GEOGCS[“Arc 1960”,
DATUM[“Arc_1960”,
SPHEROID[“Clarke 1880 (RGS)”,6378249.145,293.465,
AUTHORITY[“EPSG”,“7012”]],
TOWGS84[-160,-6,-302,0,0,0,0],
AUTHORITY[“EPSG”,“6210”]],
PRIMEM[“Greenwich”,0,
AUTHORITY[“EPSG”,“8901”]],
UNIT[“degree”,0.0174532925199433,
AUTHORITY[“EPSG”,“9122”]],
AUTHORITY[“EPSG”,“4210”]]

It should be there. You can use the Location Wizard to select this
EPSG code.

BUT: I just tried and the datum is not recognised:

g.proj -w
GEOGCS[“clark80”,
DATUM[“unknown”,
SPHEROID[“Clarke_1880”,6378249.145,293.465]],
PRIMEM[“Greenwich”,0],
UNIT[“degree”,0.0174532925199433]]

Do these tickets strike back?
http://trac.osgeo.org/grass/ticket/1452
http://trac.osgeo.org/grass/ticket/1748

Markus