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

[Paragon Corporation]

I think UTMs are offset to be postive, but transforming is not going to
verify that it will stay positive.

The transform simply does some math and if you start out with an incorrect
SRID and try to transform to another you get in return something equally
bogus.  It doesn't validate to make sure that what you transformed to is
within the boundaries of the spatial reference system.  Although I suppose
it might be a nice feature.  Then you will know you did something wrong or
your  initial SRID guess was wrong.

On another note you have a typo - I think you meant to say 2204 is ... But
that is neither here nor there.  2204 is obviously not the right SRID for
that point.

I think your first guess 4267 is probably right.

Hope that helps,
Regina




-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Don
Sent: Monday, May 19, 2008 8:05 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] couldn't get the correct projected values

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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