[OSRS-PROJ] Older Stateplane Definitions ???

[Frank Warmerdam]

Gerald Evenden wrote:

> All longitude is from the geographic coordinate origin *which is not*
> *explicitly defined.*  So it can just as well be relative to the French 
> origin.
> The later, proj, definitioin is not in error unless one assumes that the
> Greenwich origin is used.
> 
> To use Greenwich data with proj one can merge the 2.33 correction into
> the lon_0 factor.

Gerald,

Indeed the problem comes in part as we try to go beyond using PROJ as a
package for transforming between projected coordinates and geographic
coordinates to converting between arbitrary coordinate systems ... a task
that wasn't originally in-scope for PROJ.  As you warned when I introduced
the datum shift code expanding PROJ into a general coordinate system to
coordinate system package leads to a variety of problems though in my
opinion they are not insolvable, and are worth addressing.

To address this I am thinking that perhaps I should add a +pm (prime
meridian) flag for PROJ.  This would basically only be used when converting
lat/long values with different prime meridians (ie. by the new cs2cs program)
and wouldn't affect the core pj_fwd() and pj_inv() actions ... much like the
datum stuff is ignored by the core code.

I am submitting the idea of the +pm flag to bugzilla as:

   http://bugzilla.remotesensing.org/show_bug.cgi?id=186

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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