OGR/EPSG problem with California State Plane?

[bdiscoe]

Hi Frank,

This "State Plant Feet" issue came up again this evening due to a 
sudden urgent need to convert to Washington State Plane North NAD83 
*Feet*.

I'm afraid that the previous discussion below leaves me wondering how 
to specify this projection to OGRSpatialReference. The problem is 
definitely the difference between Meters and Feet.

Should i set the projection, then force the units to feet, and 
get/set the parameters to convert the false easting/northing from 
meters to feet?? Is there any way to simply tell it to use feet?

Regarding "defined by law, California 3 zone 3 in NAD83 is meters"
Can you point me to this law? I searched the Web for hours in vain. 
All the GIS data i have yet encountered in State Plane coordinates 
has been Feet, and all the GIS data providers have acted as if Feet 
is the correct and only units used.

It seems that the EPSG database makes the convenient simplification 
of putting all values in meters, however this may not reflect the 
actual standards and common use.

Thanks,
Ben
(please CC: ben.discoe at i...)

--- In gdal-dev at y..., Frank Warmerdam <warmerdam at p...> wrote:
> >>From: Ben Discoe [mailto:ben at v...]
> >>Sent: Saturday, January 19, 2002 1:21 AM
> >>To: gdal-dev at y...
> >>Subject: [gdal-dev] OGR/EPSG problem with California State Plane?
> >>
> >>
> >>I've spent the past day trying to track down a problem with some
> >>GIS data i've acquired from the City of Palo Alto. They say that
> >>the data uses California State Plane, Zone 3, NAD83.
> >>
> >>When i use OGRSpatialReference to operate on these coordinates,
> >>i get very incorrect results.
> >>
> >>I've tracked down the problem to the set of parameters used to
> >>describe the projection. They parameters are looked up by
> >>EPSGGetProjTRFInfo() which consults the file
> >>"gdal/data/trf_nonpolynomial.csv", and gets the following
> >>data from the file:
> >>
> >>10433 California CS83 zone 3 [..] 36.3 -120.3 38.26 37.04 
2000000 500000
> >>
> >>That is:
> >>standard parallel 1 38.4333333333
> >>standard parallel 2 37.0666666666
> >>center latitude 36.5
> >>center longitude -120.5
> >>false easting 2000000
> >>false northing 500000
> >>
> >>But, according to one online reference, the correct values are:
> >>False Easting: 6561666.6666
> >>False Northing: 1640416.6666
> 
> Ben,
> 
> The csv files are derived from the EPSG 4.3 database. While it
> possible that it has errors, it is unlikely that there are alot
> on something as important as state plane zones.
> 
> I notice the difference in easting and northing is exactly the
> factor of the us foot vs. meter.
> 
> In other words, you are expressing the false easting and northing
> in us feet while the database expresses them in meters. A dump in
> wkt of the database for california NAD83 zone 3 shows:
> 
> PROJCS["NAD83 / California zone 3",
> GEOGCS["NAD83",
> DATUM["North_American_Datum_1983",
> SPHEROID["GRS 1980",6378137,298.257222101,
> AUTHORITY["EPSG",7019]],
> TOWGS84[0,0,0,0,0,0,0],
> AUTHORITY["EPSG",6269]],
> PRIMEM["Greenwich",0,
> AUTHORITY["EPSG",8901]],
> UNIT["degree",0.0174532925199433],
> AUTHORITY["EPSG",4269]],
> PROJECTION["Lambert_Conformal_Conic_2SP"],
> PARAMETER["standard_parallel_1",38.4333333333333],
> PARAMETER["standard_parallel_2",37.0666666666667],
> PARAMETER["latitude_of_origin",36.5],
> PARAMETER["central_meridian",-120.5],
> PARAMETER["false_easting",2000000],
> PARAMETER["false_northing",500000],
> UNIT["metre",1,
> AUTHORITY["EPSG",9001]],
> AUTHORITY["EPSG",26943]]
> 
> Note that the overall units for zone are meters. As defined by
> law, California 3 zone 3 in NAD83 is always supposed to be
> operated on in meters. Of course, some organizations and
> projects still operate in feet anyways. Perhaps your data does?
> 
> Note, that if you use the same WKT definition, but with the units
> being feet the false northings and eastings still have to be
> expressed in meters.