[GRASS-dev] [bug #5454] (grass) ps.map scaling not correct when projection units are feet

[Glynn Clements]

Hamish wrote:

> > this bug's URL: http://intevation.de/rt/webrt?serial_num=5454
> > ---------------------------------------------------------------------
> > 
> > Subject: ps.map scaling not correct when projection units are feet
> 
> fixed in 6.3-CVS and 6.2 release branch. Also fixes bug #3096.
> 
> 
> outstanding issue, due to :
> 
> > > > and a PROJ_UNITS file of:
> > > > unit: US survey foot
> > > > units: US survey foots
> Hamish:
> > > foots?            ^^^^^^^

I know that "US English" tends to prefer simply tacking an "s" on the
end to using irregular plurals (e.g. "datums" rather than "data"), but
that's taking it a bit far ;)

> Tom:
> > That's what it picked on its own.  I think the function that chooses
> > the plural just tacks an "s" on the end except under very specific
> > conditions.
> 
> lib/gis/proj2.c, proj3.c have some pluralizing magic, but in this case
> that's the way it's stored in the PROJ_UNITS file created from EPSG code
> #2258.
> 
> 
> G63> g.proj -p
> -PROJ_INFO-------------------------------------------------
> name       : Transverse Mercator
> proj       : tmerc
> datum      : nad83
> ellps      : grs80
> lat_0      : 31
> lon_0      : -106.25
> k          : 0.999900
> x_0        : 500000.0001016001
> y_0        : 0
> no_defs    : defined
> -PROJ_UNITS------------------------------------------------
> unit       : US survey foot
> units      : US survey foots
> meters     : 0.3048006096012192
> 
> 
> the only place I see "US survey foot" in the code is one line in
> lib/proj/unit_of_measure.csv. 
> 
> Create new locn from EPSG code is in general/g.proj/output.c,
> but I don't really follow it.

AFAICT, the problem is with GPJ_osr_to_grass(); lib/proj/convert.c:

592        dfToMeters = OSRGetLinearUnits( hSRS, &pszUnitsName );
593        
594        /* Workaround for the most obvious case when unit name is unknown */
595        if( (strcasecmp(pszUnitsName, "unknown") == 0) && (dfToMeters == 1.) )
596            G_asprintf( &pszUnitsName, "meter" );
597       
598        G_set_key_value( "unit", pszUnitsName, *projunits );
599        sprintf( szFormatBuf, "%ss", pszUnitsName );
600        G_set_key_value( "units", szFormatBuf, *projunits );

AFAICT, the OGR API doesn't provide a mechanism to get the plural
name, so the code will need to handle it as a special case, e.g.:

	if (G_strcasecmp(pszUnitsName, "foot") == 0)
		strcpy( szFormatBuf, "feet" );
	else
		sprintf( szFormatBuf, "%ss", pszUnitsName );

[Do we also need to handle "inchs"? ;) ]

Alternatively, it could use general/g.setproj/proj-units.table, which
has the singular and plural forms for all of the likely units (and
some rather unlikely ones, e.g. decinanometers).

-- 
Glynn Clements <glynn at gclements.plus.com>