[GRASS5] datum transforms...

Frank Warmerdam warmerdam at pobox.com
Wed Jan 15 09:13:29 EST 2003

Paul Kelly wrote:
> +}
> diff -ru grass50_exp_2003_01_10/src/libes/proj/pj_datums.c grass/src/libes/proj/pj_datums.c
> --- grass50_exp_2003_01_10/src/libes/proj/pj_datums.c	2002-05-31 04:12:41.000000000 +0100
> +++ grass/src/libes/proj/pj_datums.c	2003-01-15 12:34:16.549358000 +0000
> @@ -56,7 +56,7 @@
>  /* id       definition                               ellipse  comments */
>  /* --       ----------                               -------  -------- */
>  "ggrs87",   "towgs84=-199.87,74.79,246.62",          "grs80", "Greek Geodetic Reference System 1987",
> -"nad27",    "nadgrids=conus,ntv1 can.dat",           "clark66", "North American Datum 1927",
> +"nad27",    "nadgrids=conus,ntv1_can.dat",           "clark66", "North American Datum 1927",
>  "wgs84",  "towgs84=0.0,0.0,0.0",  "wgs84",  "World Geodetic System 1984",
>  "wgs72",  "towgs84=0.0,0.0,5.0",  "wgs72",  "World Geodetic System 1972",
>  "nad83",  "towgs84=0.0,0.0,0.0",  "grs80",  "North American 1983",
> @@ -79,5 +79,6 @@
>  "potsdam",  "towgs84=606.0,23.0,413.0",  "bessel",  "Potsdam Rauenberg 1950 DHDN",
>  "carthage",  "towgs84=-263.0,6.0,431.0",  "clark80",  "Carthage 1934 Tunisia",
>  "hermannskogel", "towgs84=653.0,-212.0,449.0",  "bessel",  "Hermannskogel",
> +"ire65",  "towgs84=482.530,-130.596,564.557,-1.042,-0.214,-0.631,8.15",  "modif_airy",  "Ireland 1965",
>  NULL,       NULL,                                    NULL,    NULL ,
>  };


In general your changes look good to me.  I am curious about a few things.
Do you have any idea how the underscores got stripped out of stuff?  They are
fine in the PROJ.4 originals.  I would note that even the underscores in the
comment fields for the datums are intended to be significant.  The comment
fields are intended to hold the full EPSG/OGC name for the datums for ease
of translation.

I have tentatively added the potsdam, carthage, hermannskogel and ire65
datums to the pj_datums.c in PROJ.4, even though I am hesitant to extend the
datums list untill such time as I have a meaningful naming convention for
the datums.  I am sticking with the upper case names for WGS84, GGRS87,
NAD83 and NAD27.  Why does GRASS seem to force these to lower case?  I hope
the comparison logic would be case insensitive.

For me, the key things are to try and minimize the differences in the core
of PROJ.4 between GRASS and the public PROJ.4 release.  In GRASS 5.1 and
beyond, as GRASS becomes more shared library oriented I would hope that
GRASS would be able to work with pre-installed PROJ.4 libraries instead of
including a static copy in libgis.  If this is ever to work we have to ensure
that the GRASS specific logic for PROJ.4 use is embedded in the GRASS
wrapper functions (such as pj_do_transform()), not in PROJ.4 code itself.

Best regards,

I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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