[GRASS-user] Correctly Converting LL to LCC

[Rich Shepard]

On Mon, 28 Dec 2009, Glynn Clements wrote:

>> cs2cs ... +x_0=1312336
> Versus:
>>     false east 1312335.958000 (International feet)
> Versus:
> 	http://trac.osgeo.org/proj/wiki/GenParms#Units
> You forgot to convert between feet and metres.

Glynn,

   Thank you. This is a point of confusion for me because the metadata from
the source shows the false easting in International feet, yet it states that
units should be in meters. I've never understood why.

> Technically, PROJ is units-agnostic. All of the values which it deals with
> are dimensionless quantities. HOWEVER: you must use the same units for
> everything. As the named ellipsoids use metres for the semi-major axis,
> x_0 must also be in metres (the false easting given above is 400000m), and
> you need to use +to_meter= if you want the resulting cartographic
> coordinates converted to feet.

   No, I want them in meters so everything matches.

> Looking for similar projections in the EPSG table (/usr/share/proj/epsg),
> I find:
>
> # NAD83 / Oregon Lambert
> <2991> +proj=lcc +lat_1=43 +lat_2=45.5 +lat_0=41.75 +lon_0=-120.5
> +x_0=400000 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs <>

   The above is what I do want.

Thank you,

Rich