[postgis-users] couldn't get the correct projected values

[Andy Anderson]

SRID 2204 (not 2202) is a Lambert Conformal Conic Projection with  
central meridian -86° and central parallel about 35.5°:

--- EPSG 2204 : NAD27 / Tennessee
---
INSERT INTO  
"spatial_ref_sys 
" ("srid","auth_name","auth_srid","srtext","proj4text") VALUES (2204,'EP
SG',2204,'PROJCS["NAD27 /  
Tennessee 
",GEOGCS["NAD27",DATUM["North_American_Datum_1927",SPHEROID["Clar
ke 1866", 
6378206.4,294.9786982138982 
,AUTHORITY["EPSG","7008"]],AUTHORITY["EPSG","6267"]],PRIMEM["Gre
enwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree", 
0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTH
ORITY 
["EPSG 
","4267 
"]],PROJECTION 
["Lambert_Conformal_Conic_2SP"],PARAMETER["standard_parallel_1",35.2
5],PARAMETER["standard_parallel_2", 
36.41666666666666],PARAMETER["latitude_of_origin",34.666666666666
66],PARAMETER["central_meridian",-86],PARAMETER["false_easting", 
2000000],PARAMETER["false_northing",
100000],UNIT["US survey foot", 
0.3048006096012192,AUTHORITY["EPSG","9003"]],AUTHORITY["EPSG","2204"]]
','+proj=lcc +lat_1=35.25 +lat_2=36.41666666666666  
+lat_0=34.66666666666666 +lon_0=-86 +x_0=609601.2
192024384 +y_0=30480.06096012192 +ellps=clrk66 +datum=NAD27  
+to_meter=0.3048006096012192 +no_defs ')

If you run GeomFromText('Point( -85.70285 35.50463)', 2204), i.e. with  
the same coordinate values as in your first example, then they will be  
interpreted differently, with respect to this projection, not as  
longitude and latitude.  So one would expect that the values you  
provide will be taken to be a small negative easting (-85.70285 feet)  
and a small positive northing (35.50463 feet). Since SRID 2204 has a  
false easting of 2,000,000 feet and a false northing of 100,000 feet  
assigned to its center point, your point will be located hundreds of  
miles to the west and tens of miles to the south of the center point.

When you then transform with respect to 26916 (UTM Zone 16N), with  
central meridian -87° and northing = 0 at the equator, the result is  
not surprisingly a negative easting and reasonable sounding northing.

In other words, your first example is the correct approach.

-- Andy 

On May 19, 2008, at 8:04 PM, Don wrote:

> I am having problems with Transform. It is giving me values which  
> don't seem correct.
> This command transforms nad27 clrk66 to UTMzone16 grs80 nad83 meters:
>
> select AsText(Transform(GeomFromText('Point( -85.70285 35.50463)',  
> 4267),'26916')) from table;
>
> I get what seems like a reasonable value.
> POINT(617641.061533109 3929788.38473634)
>
> However if I run this command:
>
> select AsText(Transform(GeomFromText('Point( -85.70285 35.50463)',  
> 2204),'26916')) from table;
>
> I get this result:
> POINT(-17819.6295321235 3799331.7285575)
> This does not look like a valid UTM coordinate.  I thought that they  
> were offset so that they are positive.
>
> SRID 2202 is defined as
> "+proj=lcc +lat_1=35.25 +lat_2=36.41666666666666  
> +lat_0=34.66666666666666 +lon_0=-86 +x_0=609601.2192024384  
> +y_0=30480.06096012192 +ellps=clrk66 +datum=NAD27  
> +to_meter=0.3048006096012192 +no_defs"
>
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