[Proj] nad27 vs. epsg defn of CA State Plane zone VII

Dardo D Kleiner - CONTRACTOR dkleiner at cmf.nrl.navy.mil
Fri Jul 22 14:12:52 EDT 2005

I think I've run into a discrepancy in the false northing value for NAD27
California State Plane zone VII between the nad27 and epsg parameter sets.

In ${PROJ_HOME}/share/proj/nad27:

# 407: california vii: nad27
<407> proj=lcc  datum=NAD27
lon_0=-118d20 lat_1=34d25 lat_2=33d52 lat_0=34d8
x_0=1276106.450596901 y_0=1268253.006858014
no_defs <> 

but in ${PROJ_HOME}/share/proj/epsg:

# NAD27 / California zone VII
<26747> +proj=lcc +lat_1=34.41666666666666 +lat_2=33.86666666666667 +lat_0=34.13333333333333 +lon_0=-118.3333333333333 +x_0=1276106.450596901 +y_0=127079.524511049 +ellps=clrk66 +datum=NAD27 +to_meter=0.3048006096012192 +no_defs  <>

Note the different values for false northing (y_0).

I downloaded the latest EPSG database and checked the values there.  That
seems to be the source of the error:

          parameter_name           | parameter_value | unit_of_meas_name 
 Latitude of false origin          |           34.08 | sexagesimal DMS
 Longitude of false origin         |          -118.2 | sexagesimal DMS
 Latitude of 1st standard parallel |           34.25 | sexagesimal DMS
 Latitude of 2nd standard parallel |           33.52 | sexagesimal DMS
 Easting at false origin           |      4186692.58 | US survey foot
 Northing at false origin          |       416926.74 | US survey foot

In fact, Northing at false origin should be 4160926.74, assuming the nad27
file has the correct value (1268253.006858014 / 0.3048006096012192).  Seems
like the zero in the thousands position was somehow dropped?!

I found this when attempting some projections, e.g.

before "fixing" ${PROJ_HOME}/share/proj/epsg to match nad27:
$ echo "4212125 4131750" | cs2cs +init=epsg:26747 +to +init=epsg:4326
118d14'19.865"W 44d16'39.181"N 0.000

which is wildly off in latitude from what I expected.

after "fixing" ${PROJ_HOME}/share/proj/epsg to match nad27:
echo "4212125 4131750" | cs2cs +init=epsg:26747 +to +init=epsg:4326
118d15'1.013"W  34d3'11.306"N 0.000

which is much closer...

Not sure where else to submit this, but I did cc the contact listed at

Dardo D. Kleiner
Connection Machine Facility, Center for Computational Sciences
Naval Research Laboratory (Washington, DC)
dkleiner at cmf.nrl.navy.mil -- 202.404.7019 

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