[postgis-users] translation of nad83 state plane meters to de cimal long / lat

[Obe, Regina DND\MIS]

It's been a while since I've done this, so I appologize for the sketchiness
of this.

1) You have to have your postgis compiled to use PROJ library

2) You have to have your spatial_ref_sys table loaded (the data is provided
with the postgis  source) the trick is to locate the SRIDs in the
spatial_ref_sys table that correspond to the spatial references you are
trying to translate back and forth to

3) Your input spatial field has to be created with a particular SRID - 
something like
SELECT AddGeometryColumn('mydb', 'mytable', 'my_input_geom', '102686',
'MULTIPOLYGON', 2);

(102686 - is the SRID for NAD83 Massachusetts feet - but you can replace
that with your SRID)

For speed purposes, you may want to store your output geometry in another
spatial field
SELECT AddGeometryColumn('mydb', 'mytable', 'my_output_geom', '26986',
'MULTIPOLYGON', 2);

26986 - is SRID for Massachusetts NAD83 longitude latitude (LCC) asI recall


3) Then you use the transform function --  something like
UPDATE mytable SET my_output_geom = transform(my_input_geom, 26986) 


-----Original Message-----
From: Tony [mailto:developer at godseye.com]
Sent: Tuesday, June 10, 2003 5:56 PM
To: postgis-users
Subject: [postgis-users] translation of nad83 state plane meters to
decimal long / lat


Hello,

This is my first time using PostGIS, and I have a stupid user question.

Does PostGIS have the functionality to translate NAD83 State Plane
Meters to decimal longitude and latitude (a reverse Lambert conversion
computation)? Does it require the provision of precomputed constants or
are those stored a priori?

I was starting to do this on my own, and thought that perhaps PostGIS
and/or Proj4 would be a cleaner method.

If someone could provide or point to an example, I would be grateful.

Thanks,
Tony Pryor




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